10 hours create the college model. Data Definition Commands. Data Manipulation commands, Data Control commands

Transcription

1 Mdule-04 STRUCTURED QUERY LANGUAGE (SQL) 4.1 Mtivatin The knwledge SQL is essential fr sftware develper hence SQL is an imprtant subject in cmputer prgramming arund the wrld. 4.2 Objective DBMS is the cncept fr the management f database but SQL is a set f tl r sftware Fr the implementatin f all the cncept. In SQL we will ging t see hw each and every cncept f DBMS is implemented with SQL. 4.3 Syllabus Prerequisites: Syllabus: Duratin: Self study: Relatinal Overview f SQL 10 hurs create the cllege mdel. Data Definitin Cmmands library database Set peratins Aggregate functin Null values, Data Manipulatin cmmands, Data Cntrl cmmands using SQL cmmand then and use all the DML, DDL, and DCL cmmand. Views in SQL Cmplex Retrieval Queries using Grup By, Recursive Queries, nested Queries ; Referential integrity in SQL. Event Cnditin Actin (ECA) mdel (Triggers) in SQL Database Prgramming with JDBC, Security and authrizatin in SQL Functins and Prcedures in SQL and cursrs. 4.4 Definitin Data definitin: SQL lets a user define the structure and rganizatin f the stred data and relatinships amng the stred data items.

2 Data retrieval: SQL allws a user r an applicatin prgram t retrieve stred data frm the database and use it. Data manipulatin: SQL allws a user r an applicatin prgram t update the database by adding new data, remving ld data, and mdifying previusly stred data. Access cntrl: SQL can be used t restrict a user s ability t retrieve, add, and mdify data, prtecting stred data against unauthrized access. Data sharing: SQL is used t crdinate data sharing by cncurrent users, ensuring that they d nt interface with ne anther. Data integrity: SQL defines integrity cnstraints in the database, prtecting in the database, prtecting it frm crruptin due t incnsistent updates r system failures. 4.5 Curse Outcme and Learning Outcme CO3:- Student shuld be able t retrieve any type f infrmatin frm a data base by frmulating cmplex queries in SQL. CO4:- Create and ppulate a RDBMS fr a real life applicatin, with cnstraints and keys, using SQL. LO:- Write queries in SQL t retrieve any type f infrmatin frm a data base. 4.6 Key definitin SQL: SQL is a tl fr rganizing, managing, and retrieving data stred by a cmputer database. SQL is a cmputer language that we use t interact with the database. In fact, SQL wrks with ne specific type f database, called a relatinal data base. Relatinal Database: A relatinal database is a database that can be perceived as a set f tables and manipulated in accrdance with the relatinal mdel f data. It cntains a set f bjects used t stre, manage, and access data. Examples f such bjects are tables, views, indexes, functins, triggers, and packages 4.7 Thery Cmmercial database systems require mre user-friendly query languages. We will lk at SQL in detail. Althugh referred t as query languages, SQL cntains facilities fr designing and mdifying the database. The relatin schemes fr the banking example are: Branch-scheme = (bname, bcity, assets)

3 Custmer-scheme = (cname, street, ccity) Depsitr-scheme = (cname, accunt#) Accunt-scheme = (bname, accunt#, balance) Lan-scheme = (bname, lan#, amunt) Brrwer-scheme = (cname, lan#) Backgrund 1. SQL has becme the standard relatinal database language. It has several parts: Data definitin language (DDL) - prvides cmmands t Define relatin schemes. Delete relatins. Create indices. Mdify schemes. Interactive data manipulatin language (DML) - a query language based n bth relatinal algebra and tuple relatinal calculus, plus cmmands t insert, delete and mdify tuples. Embedded data manipulatin language - fr use within prgramming languages like C, PL/1, Cbl, Pascal, etc. View Definitin - cmmands fr defining views Authrizatin - specifying access rights t relatins and views. Integrity - a limited frm f integrity checking. Transactin cntrl - specifying beginning and end f transactins Basic Structure 1. Basic structure f an SQL expressin cnsists f select, frm and where clauses. select clause lists attributes t be cpied - crrespnds t relatinal algebra prject. frm clause crrespnds t Cartesian prduct - lists relatins t be used. where clause crrespnds t selectin predicate in relatinal algebra. 2. Typical query has the frm Select A1,A2..An frm R1,R2 Rn where P where each Ai represents an attribute, each Ri a relatin, and P is a predicate.

4 3. This is equivalent t the relatinal algebra expressin a1,a2..an( p(r1*r2* *Rm)) If the where clause is mitted, the predicate P is true. The list f attributes can be replaced with a * t select all. SQL frms the Cartesian prduct f the relatins named, perfrms a selectin using the predicate, then prjects the result nt the attributes named. The result f an SQL query is a relatin. SQL may internally cnvert int mre efficient expressins. The select Clause The where Clause The frm Clause The Rename Operatin Tuple Variables String Operatins Ordering the Display f Tuples Duplicate Tuples The select Clause 1. An example: Find the names f all branches in the accunt relatin. select bname frm accunt 2. distinct vs. all: eliminatin r nt eliminatin f duplicates. Find the names f all branches in the accunt relatin. select distinct bname frm accunt By default, duplicates are nt remved. We can state it explicitly using all. select all bname frm accunt 3. select * means select all the attributes. Arithmetic peratins can als be in the selectin list. The where Clause 1. The predicates can be mre cmplicated, and can invlve Lgical cnnectives and, r and nt.

5 Arithmetic expressins n cnstant r tuple values. The between peratr fr ranges f values. Example: Find accunt number f accunts with balances between $90,000 and $100,000. select accunt# frm accunt where balance between and The frm Clause 1. The frm class by itself defines a Cartesian prduct f the relatins in the clause. 2. SQL des nt have a natural jin equivalent. Hwever, natural jin can be expressed in terms f a Cartesian prduct, selectin, and prjectin. 3. Fr the relatinal algebra expressin Πename,lan#(brrwer1 lan) we can write in SQL, select distinct cname, brrwer.lan# frm brrwer, lan where brrwer.lan# = lan.lan# 4. Mre selectins with jin: ``Find the names and lan numbers f all custmers wh have a lan at the SFU branch,'' we can write in SQL, select distinct cname, brrwer.lan# frm brrwer, lan where brrwer.lan# = lan.lan# and bname=``sfu'' The Rename Operatin 1. Rename: a mechanism t rename bth relatins and attributes. 2. as-clause can appear in bth the select and frm clauses: ld-name as new-name. Example. select distinct cname, brrwer.lan# as lan_id frm brrwer, lan where brrwer.lan# = lan.lan# and bname= ``SFU" Tuple Variables 1. Tuple variables can be used in SQL, and are defined in the frm clause:

6 select distinct cname, T.lan# frm brrwer as S, lan as T where S.lan# = T.lan# 2. These variables can then be used thrughut the expressin. Think f it as being smething like the rename peratr. Finds the names f all branches that have assets greater than at least ne branch lcated in Burnaby. select distinct T.bname frm branch S, branch T where S.bcity=``Burnaby'' and T.assets > S.assets String Operatins 1. The mst cmmnly used peratin n strings is pattern matching using the peratr like. 2. String matching peratrs % (any substring) and _ (underscre, matching any character). E.g., `` %'' matches any string with at least 3 characters. 3. Patterns are case sensitive, e.g., ``Jim" des nt match ``jim". 4. Use the keywrd escape t define the escape character. E.g., like ``ab%tely % '' escape `` '' matches all the strings beginning with ``ab'' fllwed by a sequence f characters and then ``tely'' and then ``% ''.Backslash verrides the special meaning f these symbls. 5. We can use nt like fr string mismatching. Example. Find all custmers whse street includes the substring ``Main''. select cname frm custmer where street like ``%Main%'' 6. SQL als permits a variety f functins n character strings, such as cncatenating (using `` ''), extracting substrings, finding the length f strings, cnverting between upper case and lwer case, and s n Ordering the Display f Tuples 1. SQL allws the user t cntrl the rder in which tuples are displayed. rder by makes tuples appear in srted rder (ascending rder by default).

7 desc specifies descending rder. asc specifies ascending rder. select * frm lan rder by amunt desc, lan# asc Srting can be cstly, and shuld nly be dne when needed Duplicate Tuples Frmal query languages are based n mathematical relatins. Thus n duplicates appear in relatins. As duplicate remval is expensive, SQL allws duplicates. T remve duplicates, we use the distinct keywrd. T ensure that duplicates are nt remved, we use the all keywrd. Multiset (bag) versins f relatinal algebra peratrs. if there are c1 cpies f tuples t1 in R1, and t1 satisfies selectin θ, then there are c1 cpies f t1 in σθ (R1). fr each cpy f tuple t1 in R1, there is a cpy f tuple a(t1) in πa(r1). if there are c1 cpies f tuple t1 in R1, and C2 cpies f tuple t2 in R2, there is C1 C2 cpies f tuple t1,t2 in R1 R2. An SQL query f the frm select A1,A2.An frm R1,R2 Rn where P is equivalent t the algebra expressin A1,A2..An(σp(R1 R2 Rm)) using the multiset versins f the relatinal peratrs σ, and. Set Operatins 1. SQL has the set peratins unin, intersect and except. 2. Find all custmers having an accunt. select distinct cname frm depsitr 3. unin: Find all custmers having a lan, an accunt, r bth. branch. (select cname

8 frm depsitr) unin (select cname frm brrwer) 4. intersect: Find custmers having a lan and an accunt. (select distinct cname frm depsitr) intersect (select distinct cname frm brrwer) 5. except: Find custmers having an accunt, but nt a lan. (select distinct cname frm depsitr) except (select cname frm brrwer) 6. Sme additinal details: unin eliminates duplicates, being a set peratin. If we want t retain duplicates, we may use unin all, similarly fr intersect and except. Nt all implementatins f SQL have these set peratins. except in SQL-92 is called minus in SQL-86. It is pssible t express these queries using ther peratins.

9 4.7.3 Aggregate Functins 1. In SQL we can cmpute functins n grups f tuples using the grup by clause. Attributes given are used t frm grups with the same values. SQL can then cmpute average value -- avg minimum value -- min maximum value -- max ttal sum f values -- sum number in grup -- cunt These are called aggregate functins. They return a single value. 2. Sme examples: 1. Find the average accunt balance at each branch. select bname, avg (balance) frm accunt grup by bname 2. Find the number f depsitrs at each branch. select bname, cunt (distinct cname) frm accunt, depsitr where accunt.accunt# = depsitr.accunt# grup by bname We use distinct s that a persn having mre than ne accunt will nt be cunted mre than nce. 3. Find branches and their average balances where the average balance is mre than $1200. select bname, avg (balance) frm accunt grup by bname having avg (balance) > 1200 Predicates in the having clause are applied after the frmatin f grups. 4. Find the average balance f each custmer wh lives in Vancuver and has at least three accunts: select depsitr.cname, avg (balance)

10 frm depsitr, accunt, custmer where depsitr.cname = custmer.cname and accunt.accunt# = depsitr.accunt# and ccity=``vancuver'' grup by depsitr.cname having cunt (distinct accunt#) >= 3 If a where clause and a having clause appear in the same query, the where clause predicate is applied first. Tuples satisfying where clause are placed int grups by the grup by clause. The having clause is applied t each grup. Grups satisfying the having clause are used by the select clause t generate the result tuples. If n having clause is present, the tuples satisfying the where clause are treated as a single grup. Null Values 1. With insertins, we saw hw null values might be needed if values were unknwn. Queries invlving nulls pse prblems. 2. If a value is nt knwn, it cannt be cmpared r be used as part f an aggregate functin. 3. All cmparisns invlving null are false by definitin. Hwever, we can use the keywrd null t test fr null values: select distinct lan# frm lan where amunt is null 4. All aggregate functins except cunt ignre tuples with null values n the argument attributes.

11 4.7.4 Nested Subqueries Set Membership Set Cmparisn Test fr Empty Relatins Test fr the Absence f Duplicate Tuples We use the in and nt in peratins fr set membership. select distinct cname frm brrwer where cname in (select cname frm accunt where bname=``sfu'') Nte that we can write the same query several ways in SQL. We can als test fr mre than ne attribute: select distinct cname frm brrwer, lan where brrwer.lan# = lan.lan# and bname=``sfu'' and (bname, cname) in frm accunt, depsitr where depsitr.accunt# = accunt.accunt#) This finds all custmers wh have a lan and an accunt at the SFU branch in yet anther way. Finding all custmers wh have a lan but nt an accunt, we can use the nt in peratin Set Cmparisn 1. T cmpare set elements in terms f inequalities, we can write select distinct T.bname frm branch T,branch S where T.assets > S.assets and S.bcity=``Burnaby'' r we can write select bname frm branch

12 where assets > sme (select assets frm branch where bcity=``burnaby'') t find branches whse assets are greater than sme branch in Burnaby. 2. We can use any f the equality r inequality peratrs with sme. If we change > sme t > all, we find branches whse assets are greater than all branches in Burnaby. 3. Example. Find branches with the highest average balance. We cannt cmpse aggregate functins in SQL, e.g. we cannt d max (avg...)). Instead, we find the branches fr which average balance is greater than r equal t all average balances: select bname frm accunt grup by bname having avg (balance) >= all (select avg (balance) frm accunt grup by bname) Test fr Empty Relatins 1. The exists cnstruct returns true if the argument subquery is nnempty. 2. Find all custmers wh have a lan and an accunt at the bank. select cname frm brrwer where exists (select * frm depsitr where depsitr.cname = brrwer.cname) Test fr the Absence f Duplicate Tuples 1. The unique cnstruct returns true if the argument subquery cntains n duplicate tuples. 2. Find all custmers wh have nly ne accunt at the SFU branch. aaaaa aa - select T.cname frm depsitr as T where unique (select R.cname

13 frm accunt, depsitr as R where T.cname = R.cname and R.accunt# = accunt.accunt# and accunt.bname = ``SFU") Derived Relatins 1. SQL-92 allws a subquery expressin t be used in the frm clause. 2. If such an expressin is used, the result relatin must be given a name, and the attributes can be renamed. 3. Find the average accunt balance f thse branches where the average accunt balance is greater than $1,000. select bname, avg-balance frm (select bname, avg(balance) frm accunt grup by bname) as result(bname, avg-balance) where avg-balance > 1000

14 4.7.6 Views 1. A view in SQL is defined using the create view cmmand: 2. create view v as query expressin where query expressin is any legal query expressin. The view created is given the name v. T create a view all-custmer f all branches and their custmers: create view all-custmer as (select bname, cname frm depsitr, accunt where depsitr.accunt# = accunt.accunt#) unin (select bname, cname frm brrwer, lan where brrwer.lan# = lan.lan#) 3. Having defined a view, we can nw use it t refer t the virtual relatin it creates. View names can appear anywhere a relatin name can. 4. We can nw find all custmers f the SFU branch by writing select cname frm all-custmer where bname=``sfu' Mdificatin f the Database Up until nw, we have lked at extracting infrmatin frm the database. Deletin Insertin Updates Update f a view Deletin 1. Deletin is expressed in much the same way as a query. Instead f displaying, the selected tuples are remved frm the database. We can nly delete whle tuples. 2. A deletin in SQL is f the frm delete frm r where P

15 Tuples in r fr which P is true are deleted. If the where clause is mitted, all tuples are deleted. 3. The request delete frm lan deletes all tuples frm the relatin lan. 4. Sme mre examples: 1. Delete all f Smith's accunt recrds. delete frm depsitr where cname=``smith'' 2.Delete all lans with lan numbers between 1300 and delete frm lan where lan# between 1300 and Delete all accunts at branches lcated in Surrey. delete frm accunt where bname in (select bname frm branch where bcity=``surrey'') 5. We may nly delete tuples frm ne relatin at a time, but we may reference any number f relatins in a select-frm-where clause embedded in the where clause f a delete. 6. Hwever, if the delete request cntains an embedded select that references the relatin frm which tuples are t be deleted, ambiguities may result. Fr example, t delete the recrds f all accunts with balances belw the average, we might write delete frm accunt where balance < (select avg(balance) frm accunt) Yu can see that as we delete tuples frm accunt, the average balance changes! Slutin: The delete statement first test each tuple in the relatin accunt t check whether the accunt has a balance less than the average f the bank. Then all tuples that fail the test are deleted. Perfrm all the tests (and mark the tuples t be deleted) befre any deletin then delete them en masse after the evaluatins! Insertin

16 1. T insert data int a relatin, we either specify a tuple, r write a query whse result is the set f tuples t be inserted. Attribute values fr inserted tuples must be members f the attribute's dmain. 2. Sme examples: 1. T insert a tuple fr Smith wh has $1200 in accunt A-9372 at the SFU branch. insert int accunt values (``SFU'', ``A-9372'', 1200) 2. T prvide each lan that the custmer has in the SFU branch with a $200 savings accunt. insert int accunt select bname, lan#, 200 frm lan where bname=``sfu'' Here, we use a select t specify a set f tuples. It is imprtant that we evaluate the select statement fully befre carrying ut any insertin. If sme insertins were carried ut even as the select statement were being evaluated, the insertin insert int accunt select * frm accunt might insert an infinite number f tuples. Evaluating the select statement cmpletely befre perfrming insertins avids such prblems. 3. It is pssible fr inserted tuples t be given values n nly sme attributes f the schema. The remaining attributes are assigned a null value dented by null. We can prhibit the insertin f null values using the SQL DDL Updates 1. Updating allws us t change sme values in a tuple withut necessarily changing all. 2. Sme examples: 1. T increase all balances by 5 percent.

17 update accunt set balance=balance * 1.05 This statement is applied t every tuple in accunt. T ke tw different rates f interest payment, depending n balance amunt: update accunt 2. set balance=balance * 1.06 where balance > 10,000 update accunt set balance=balance * 1.05 where balance 10,000 Nte: in this example the rder f the tw peratins is imprtant. (Why?) 3. In general, where clause f update statement may cntain any cnstruct legal in a where clause f a select statement (including nesting). 4. A nested select within an update may reference the relatin that is being updated. As befre, all tuples in the relatin are first tested t see whether they shuld be updated, and the updates are carried ut afterwards. Fr example, t pay 5% interest n accunt whse balance is greater than average, we have update accunt set balance=balance * 1.05 where balance > select avg (balance) frm accunt Update f a view 1. The view update anmaly previusly mentined in Chapter 3 exists als in SQL. 2. An example will illustrate: cnsider a clerk wh needs t see all infrmatin in the lan relatin except amunt. Let the view branch-lan be given t the clerk: create view branch-lan as select bname, lan# frm lan

18 Since SQL allws a view name t appear anywhere a relatin name may appear, the clerk can write: insert int branch-lan values (``SFU'', ``L-307'') This insertin is represented by an insertin int the actual relatin lan, frm which the view is cnstructed. Hwever, we have n value fr amunt. This insertin results in (``SFU'', ``L-307'', null) being inserted int the lan relatin. As we saw, when a view is defined in terms f several relatins, serius prblems can result. As a result, many SQL-based systems impse the cnstraint that a mdificatin is permitted thrugh a view nly if the view in questin is defined in terms f ne relatin in the database.

19 4.7.7 Jined Relatins Examples Jin types and cnditins Examples 1. Tw given relatins: lan and brrwer. Figure 4.1: The lan and brrwer relatins. 2. inner jin: lan inner jin brrwer n lan.lan# = brrwer.lan# Ntice that the lan# will appear twice in the inner jined relatin. Figure 4.2: Result f lan inner jin brrwer. 3. left uter jin: lan left uter jin brrwer n lan.lan# = brrwer.lan# Figure 4.3: Result f lan left uter jin brrwer. 4. natural inner jin: lan natural inner jin brrwer Figure 4.4: Result f lan natural inner jin brrwer Jin types and cnditins 1. Each variant f the jin peratins in SQL-92 cnsists f a jin type and a jin cnditin. 2. Jin types: inner jin, left uter jin, right uter jin, full uter jin.

20 The keywrd inner and uter are ptinal since the rest f the jin type enables us t deduce whether the jin is an inner jin r an uter jin. SQL-92 als prvides tw ther jin types: 1. crss jin: an inner jin withut a jin cnditin. 2. unin jin: a full uter jin n the ``false'' cnditin, i.e., where the inner jin is empty. 3. Jin cnditins: natural, n predicate, using (A1,A2,.An) The use f jin cnditin is mandatry fr uter jins, but is ptinal fr inner jins (if it is mitted, a Cartesian prduct results). 4. Ex. A natural full uter jin: lan natural full uter jin brrwer using (lan#) Figure 4.5: Result f lan natural full uter jin brrwer using (lan#). 5. Ex. Find all custmers wh have either an accunt r a lan (but nt bth) at the bank. select cname frm (natural full uter jin brrwer) where accunt# is null r lan# is null

21 4.7.8 Trigger A trigger is an event-cnditin-actin (ECA) rule When event ccurs, test cnditin; if cnditin is satisfied, execute actin Example: Event: sme user s ppularity is updated Cnditin: the user is a member f Jessica s Circle, and pp drps belw 0.5 Actin: kick that user ut f Jessica s Circle A trigger is a PL/SQL blck structure which is fired when a DML statements like Insert, Delete, Update is executed n a database table. A trigger is triggered autmatically when an assciated DML statement is executed. In ther wrds Triggers are a stred PL/SQL cde blck attached and executed by an event which ccurs t a database table. Triggers are stred as text and cmpiled at executin time, because f wise nt t include much cde in them but t call ut previusly stred prcedures r packages. Triggers cntained SQL r PL/SQL statements which are executed as a unit and can call ther prcedures and triggers. Triggers are used t imprve the perfrmance f Oracle in rder t prvide a mre cnvenient database. A trigger may nt issue any transactin cntrl statements like Cmmit, Rllback and Savepint. Unlike the stred prcedure and functins, which have t be called explicitly, the database triggers are fires (executed) r called implicitly whenever the table is affected by any f the abve said DML peratins. When des the Trigger Fire? A trigger fires based n a triggering statement, which specifies: The SQL statement r the database event r DDL event that fires the trigger bdy. The ptins include DELETE, INSERT, and UPDATE. One, tw, r all three f these ptins can be included in the triggering statement specificatin. The table, view, DATABASE, r SCHEMA n which the trigger is defined. Creating Trigger T create a trigger, use the CREATE TRIGGER statement. By default, a trigger is created in enabled state. T create a trigger in disabled state, use the DISABLE clause f the CREATE TRIGGER statement. Yu must have the privilege.i.e. CREATE TRIGGER.

22 Syntax: CREATE [OR REPLACE] TRIGGER trigge_name {BEFORE! AFTER I INSTEAD OF} {INSERT [OR]! UPDATE [OR] I DELETE} [OF cl_name] ON table_name [REFERENCING OLD AS ld, NEW AS new] [FOR EACH ROW] WHEN (cnditin) BEGIN - Sql statements END; Where: CREATE [OR REPLACE] TRIGGER trigger_name -This clause creates a trigger with the given name r verwrites an existing trigger with the same name. {BEFORE I AFTER I INSTEAD OF} - This clause indicates at what time the trigger shuld get fired. i.e. fr example: befre r after updating a table. INSTEAD OF is used t create a trigger n a view. Befre and after cannt be used t create a trigger n a view. {INSERT [OR] I UPDATE [OR] I DELETE} - This clause determines the triggering event. Mre than ne triggering events can be used tgether separated by OR keywrd. The trigger gets fired at all the specified triggering event. [OF cl_name] - This clause is used with update triggers. This clause is used when yu want t trigger an event nly when a specific clumn is updated. [ON table_name] - This clause identifies the name f the table r view t which the trigger is assciated. [REFERENCING OLD AS ld, NEW AS new] - This clause is used t reference the ld and new values f the data being changed. By default, yu reference the values as: ld.clumn_name r: new.clumn_name. The reference names can als be changed frm ld (r new) t any ther user-defined name. Yu cannt reference ld values when inserting a recrd, r new values when deleting a recrd, because they d nt exist. [FOR EACH ROW] - This clause is used t determine whether a trigger must fire when each rw gets affected (i.e. a Rw Level Trigger) r just nce when the entire sql statement is executed (i.e. statement level Trigger).

23 WHEN (cnditin) - This clause is valid nly fr rw level triggers. The trigger is fired nly fr rws that satisfy the cnditin specified. Parts f a Trigger A trigger has three basic parts: A triggering event r statement A trigger restrictin A trigger actin A triggering event can be an insert, update, r delete statement r an instance shutdwn r startup etc. The trigger fires autmatically when any f these events ccur a trigger cnstraint specifies a Blean expressin that must be true fr the trigger t fire. This cnditin is specified using the WHEN clause. The trigger actin is a prcedure that cntains the cde t be executed when the trigger fires. The Triggering Event r Statement A triggering event r statement is the SQL statement, database event, r user event that causes a trigger t fire. A triggering event can be ne r mre f the fllwing: An INSERT, UPDATE, r DELETE statement n a specific table (r view, in sme cases) II A CREATE, ALTER, r DROP statement n any schema bject II A database startup r instance shutdwn II A specific errr message r any errr message II A user lgn r lgff Syntax: [INSERT DELETE UPDATE f clumn-list] ON <table-name> [REFERENCING <OLD as ld, NEW as new>] A triggering event can specify multiple SQL statements: [... INSERT OR UPDATE OR DELETE OF inventry... ] This part means that when an INSERT, UPDATE, r DELETE statement is issued against the inventry table, fire the trigger. When multiple types f SQL statements can fire a trigger, yu can use cnditinal predicates t detect the type f triggering statement.

24 Trigger Restrictin A trigger restrictin specifies a Blean expressin that must be true fr the trigger t fire. The trigger actin is nt run if the trigger restrictin evaluates t false r unknwn in the example, the trigger restrictin is: new.parts_n_hand < new. rerder_pint Cnsequently, the trigger des nt fire unless the number f available parts is less than a present rerder amunt. Trigger Actin The trigger actin is a prcedure that cntains the cde t be executed when the trigger fires. Oracle will execute the blck when a triggering statement is issued and the trigger restrictin evaluates t true. [DECLARE] BEGIN [EXCEPTION SECTION] END [trigger-name] Types f PL/SQL Triggers A DML trigger is fired by a DML statement, a DDL trigger is fired by a DDL statement, a DELETE trigger is fired by a DELETE statement, and s n. Different types f triggers are as under: Rw Triggers and Statement Triggers BEFORE and AFTER Triggers INSTEAD OF Triggers Triggers n System Events and User Events Rw Triggers and Statement Triggers When yu define a trigger, yu can specify the number f times the trigger actin is t be run: Once fr every rw affected by the triggering statement, such as a trigger fired by an UPDATE statement that updates many rws. Once fr the triggering statement, n matter hw many rws it affects.

25 Rw Triggers A rw trigger is fired each time the table is affected by the triggering statement. Fr example, if an UPDATE statement updates multiple rws f a table, a rw trigger is fired nce fr each rw affected by the UPDATE statement. If a triggering statement affects n rws, a rw trigger is nt run. A Rw trigger fires nce fr each rw affected. It uses FOR EACH ROW clause. They are useful if trigger actin depends n number f rws affected. Rw triggers are useful if the cde in the trigger actin depends n data prvided by the triggering statement r rws that are affected. Statement Triggers A statement trigger is fired nce n behalf f the triggering statement, regardless f the number f rws in the table that the triggering statement affects, even if n rws are affected. Fr example, if a DELETE statement deletes several rws frm a table, statementlevel DELETE trigger is fired nly nce. In ther wrds Statement Trigger fires nce, irrespective f number f rws affected in the table. Statement triggers are useful when triggers actin des nt depend n Statement triggers are useful if the cde in the trigger actin des nt depend n the data prvided by the triggering statement r the rws affected. Fr example, use a statement trigger t: Make a cmplex security check n the current time r user. Generate a single audit recrd. Befre and after Triggers 'When defining a trigger, yu can specify the trigger timing-whether the trigger actin is t be run befre r after the triggering statement. BEFORE and AFTER apply t bth statement and rw triggers. BEFORE and AFTER triggers fired by DML statements can be defined nly n tables, nt n views. Hwever, triggers n the base tables f a view are fired if an INSERT, UPDATE, r DELETE statement is issued against the view. BEFORE and AFTER triggers fired by DDL statements can be defined nly n the database r a schema, nt n particular tables. Befre Triggers

26 BEFORE triggers run the trigger actin befre the triggering statement is run. This type f trigger is cmmnly used in the fllwing situatins: When the trigger actin determines whether the triggering statement shuld be allwed t cmplete. Using a BEFORE trigger fr this purpse, yu can eliminate unnecessary prcessing f the triggering statement and its eventual rllback in cases where an exceptin is raised in the trigger actin. T derive specific clumn values befre cmpleting a triggering INSERT r UPDATE statement. After Triggers AFTER triggers run the trigger actin after the triggering statement is run. AFTER TRIGGERS are used when yu want the triggering statement t cmplete befre executing the trigger actin. Instead f Triggers INSTEAD OF triggers prvide a transparent way f mdifying views that cannt be mdified directly thrugh DML statements (INSERT, UPDATE, and DELETE). These triggers are called INSTEAD OF triggers because, unlike ther types f triggers, Oracle fires the trigger instead f executing the triggering statement. Yu can write nrmal INSERT, UPDATE, and DELETE statements against the view, and the INSTEAD OF trigger is fired t update the underlying tables apprpriately INSTEAD OF triggers are activated fr each rw f the view that gets mdified Prcedure A stred prcedure is nthing mre than prepared SQL cde that yu save s yu can reuse the cde ver and ver again. S if yu think abut a query that yu write ver and ver again, instead f having t write that query each time yu wuld save it as a stred prcedure and then just call the stred prcedure t execute the SQL cde that yu saved as part f the stred prcedure. In additin t running the same SQL cde ver and ver again yu als have the ability t pass parameters t the stred prcedure, s depending n what the need is the stred prcedure can act accrdingly based n the parameter values that were passed. Befre yu create a stred prcedure yu need t knw what yur end result is, whether yu are selecting data, inserting data, etc..

27 In this simple example we will just select all data frm the Persn.Address table that is stred in the AdventureWrks database. S the simple T-SQL cde excuting in the AdventureWrks database wuld be as fllws which will return all rws frm this table. SELECT * FROM Persn.Address T create a stred prcedure t d this the cde wuld lk like this: USE AdventureWrks GO CREATE PROCEDURE db.uspgetaddress AS SELECT * FROM Persn.Address GO T call the prcedure t return the cntents frm the table specified, the cde wuld be: EXEC db.uspgetaddress -- r EXEC uspgetaddress --r just simply uspgetaddress When creating a stred prcedure yu can either use CREATE PROCEDURE r CREATE PROC. After the stred prcedure name yu need t use the keywrd "AS" and then the rest is just the regular SQL cde that yu wuld nrmally execute. One thing t nte is that yu cannt use the keywrd "GO" in the stred prcedure. Once the SQL Server cmpiler sees "GO" it assumes it is the end f the batch. Als, yu can nt change database cntext within the stred prcedure such as using "USE dbname" the reasn fr this is because this wuld be a separate batch and a stred prcedure is a cllectin f nly ne batch f statements. Just like yu have the ability t use parameters with yur SQL cde yu can als setup yur stred prcedures t accept ne r mre parameter values. One Parameter

28 In this example we will query the Persn.Address table frm the AdventureWrks database, but instead f getting back all recrds we will limit it t just a particular city. This example assumes there will be an exact match n the City value that is passed. USE AdventureWrks GO CREATE PROCEDURE nvarchar(30) AS SELECT * FROM Persn.Address WHERE City GO T call this stred prcedure we wuld execute it as fllws: EXEC = 'New Yrk' We can als d the same thing, but allw the users t give us a starting pint t search the data. Here we can change the "=" t a LIKE and use the "%" wildcard. USE AdventureWrks GO CREATE PROCEDURE nvarchar(30) AS SELECT * FROM Persn.Address WHERE City + '%' GO In bth f the prceeding examples it assumes that a parameter value will always be passed. If yu try t execute the prcedure withut passing a parameter value yu will get an errr message such as the fllwing: Msg 201, Level 16, State 4, Prcedure uspgetaddress, Line 0 Prcedure r functin 'uspgetaddress' expects parameter '@City', which was nt supplied.

29 Default Parameter Values In mst cases it is always a gd practice t pass in all parameter values, but smetimes it is nt pssible. S in this example we use the NULL ptin t allw yu t nt pass in a parameter value. If we create and run this stred prcedure as is it will nt return any data, because it is lking fr any City values that equal NULL. USE AdventureWrks GO CREATE PROCEDURE nvarchar(30) = NULL AS SELECT * FROM Persn.Address WHERE City GO We culd change this stred prcedure and use the ISNULL functin t get arund this. S if a value is passed it will use the value t narrw the result set and if a value is nt passed it will return all recrds. (Nte: if the City clumn has NULL values this will nt include these values. Yu will have t add additinal lgic fr City IS NULL) USE AdventureWrks GO CREATE PROCEDURE nvarchar(30) = NULL AS SELECT * FROM Persn.Address WHERE City = ISNULL(@City,City) GO Multiple Parameters Setting up multiple parameters is very easy t d. Yu just need t list each parameter and the data type separated by a cmma as shwn belw.

30 USE AdventureWrks GO CREATE PROCEDURE nvarchar(30) = nvarchar(60) = NULL AS SELECT * FROM Persn.Address WHERE City = ISNULL(@City,City) AND AddressLine1 LIKE '%' + ISNULL(@AddressLine1,AddressLine1) + '%' GO T execute this yu culd d any f the fllwing: EXEC = 'Calgary' --r EXEC = = 'A' --r EXEC = 'Acardia' -- etc... Setting up utput paramters fr a stred prcedure is basically the same as setting up input parameters, the nly difference is that yu use the OUTPUT clause after the parameter name t specify that it shuld return a value. The utput clause can be specified by either using the keywrd "OUTPUT" r just "OUT". Fr these examples we are still using the AdventureWrks database, s all the stred prcedures shuld be created in the AdventureWrks database. Simple Output CREATE PROCEDURE int OUTPUT AS = cunt(*) FROM AdventureWrks.Persn.Address WHERE City

31 Or it can be dne this way: CREATE PROCEDURE int OUT AS = cunt(*) FROM AdventureWrks.Persn.Address WHERE City T call this stred prcedure we wuld execute it as fllws. First we are ging t declare a variable, execute the stred prcedure and then select the returned valued. int EXEC = OUTPUT This can als be dne as fllws, where the stred prcedure parameter names are nt passed. int EXEC db.uspgetaddresscunt OUTPUT Drpping Single Stred Prcedure T drp a single stred prcedure yu use the DROP PROCEDURE r DROP PROC cmmand as fllws. DROP PROCEDURE db.uspgetaddress GO -- r DROP PROC db.uspgetaddress GO Drpping Multiple Stred Prcedures T drp multiple stred prcedures with ne cmmand yu specify each prcedure separated by a cmma as shwn belw. DROP PROCEDURE db.uspgetaddress, db.uspinsertaddress, db.uspdeleteaddress

32 GO -- r DROP PROC db.uspgetaddress, db.uspinsertaddress, db.uspdeleteaddress GO Mdifying an Existing Stred Prcedure Let's say we have the fllwing existing stred prcedure: This allws us t d an exact match n the City. CREATE PROCEDURE nvarchar(30) AS SELECT * FROM Persn.Address WHERE City GO Let's say we want t change this t d a LIKE instead f an equals. T change the stred prcedure and save the updated cde yu wuld use the ALTER PROCEDURE cmmand as fllws. ALTER PROCEDURE nvarchar(30) AS SELECT * FROM Persn.Address WHERE City + '%' GO Cursr Oracle uses wrk areas t execute SQL statements and stre prcessing infrmatin. A PL/SQL cnstruct called a CURSOR lets yu name a wrk area and access its stred infrmatin. A Cursr in its simplest frm can be thught f as a pinter t the recrds in database table r a virtual table represented by the result f a SELECT statement. A cursr is a temprary wrk area created in the system memry when a SQL statement is executed. A cursr cntains infrmatin n a select statement and the rws f data accessed

33 by it. This temprary wrk area is used t stre the data retrieved frm the database, and manipulate this data. A cursr can hld mre than ne rw, but can prcess nly ne rw at a time. The set f rws the cursr hlds is called the active set. A cursr is basically a set f rws that yu can access ne at a time. These are created by default when DML statements like, INSERT, UPDATE, and DELETE statements are executed. They are als created when a SELECT statement that returns just ne rw is executed. Explicit cursrs must be created when yu are executing a SELECT statement that returns mre than ne rw. Even thugh the cursr stres multiple recrds, nly ne recrd can be prcessed at a time, which is called as current rw. When yu fetch a rw the current rw psitin mves t next rw. Bth implicit and explicit cursrs have the same functinality, but they differ in the way they are accessed. Example: SQL) SELECT EMPNO, ENAME, JOB FROM EMP WHERE DEPTNO=20; The set f rws returned by a multi-rw query is called the result set. Its size is the number f rws that meet yur search criteria. As Figure shws, an explicit cursr "pints" t the current rw in the result set. This allws yur prgram t prcess the rws ne at a time. Types f Cursrs Yu have lts f ptins in PL/SQL fr executing SQL, and all f them ccur as sme type f cursr. Generally, there are tw types f SQL that yu can execute in PL/SQL. There are tw types f cursrs in PL/SQL: Implicit cursrs Explicit cursrs Implicit Cursrs When yu execute DML statements like Delete, Insert, Update and Select statements, implicit statements are created t prcess these statements. Oracle prvides few attributes called as implicit cursr attributes t check the status f DML peratins. The cursr attributes available are %FOUND, %NOTFOUND, %ROWCOUNT, and %ISOPEN. The values f the cursr attributes always refer t the mst recently executed SQL statement. Befre Oracle pens the SQL cursr, the implicit cursr attributes yield NULL. Fr example, when yu execute INSERT, UPDATE, r DELETE statements the cursr attributes tell us whether any rws are affected and hw many have been affected. When a

34 SELECT... INTO statement is executed in a PL/SQL Blck, implicit cursr attributes can be used t find ut whether any rw has been returned by the SELECT statement. PL/SQL returns an errr when n data is selected. Explicit Cursrs When yu need precise cntrl ver query prcessing, yu can explicitly declare a cursr in the declarative part f any PL/SQL blck, subprgram, r package. An explicit cursr is defined in the declaratin sectin f the PL/SQL Blck. It is created n a SELECT Statement which returns mre than ne rw. We can prvide a suitable name fr the cursr. 4.8 Objective questin 1) SQL stand fr. A) Syntax query language B) Structure Query Language. C) Structure quantum language. D) Nne f these. 2) Create is cmmand. A) DML. B) DCL. C) DDL D) All f them. 3) Where clause in SQL is use t define? A) Cnditin. B) Entity. C) Attribute. D) Set f tuple. 4) Sigma peratr in SQL represents. A) Select rw. B) Select clumn. C) Select set f tuple. D) All f these. 5) Rll back cmmand is A) DDL B) DML.

35 C) DCL. D) Nne f these. 6) Cmmand is use t erase the all the data f table. A) DELET. B) TRUNCATE. C) UPDATE D) WHERE 7) Frm clause in SQL refer t A) ROW. B) COLUMN. C) TABLE. D) DATABASE. 8) Fllwing functin is nt aggregate functin. A) Min. B) Max. C) Cunt. D) All f these. 9) * in SQL is use fr selectin f A) All rws. B) All clumns. C) All table. D) All f these. 10) Aggregate functin can be use nly in. A) Select clause. B) WHERE cause. C) FROM clause. D) All f these. 4.9 Subjective questin: 1) List and explain the name f all the DDL cmmand. 2) List and explain all the DML cmmand. 3) Give the name f all aggregate functin and explain.

36 4) Explain the grup by having clause with example. 5) Give the shrt nte with example. A) UNION B) INTERSECTION 6) List the set f all peratrs in SQL. 7) What is the DCL cmmand explains with example. 8) Create the any five table f library system with 10 entries in each table. 9) Explain COMMIT and ROLLBACK cmmand in SQL. Lng Answer Questin 1. List and explain the name f all the DDL cmmand. (10 Marks) 2. List and explain all the DML cmmand. (10 Marks) 3. Give the name f all aggregate functin and explain. (10 Marks) 4. Create the any five table f library system with 10 entries in each table. 5. Create the any five table f University with 10 entries in each table with all cnstrains University exam questin 1) what is SQL? Explain the fllwing structures f SQL queries with apprpriate Example i) Select clause iv) Aggregate functin ii) Where clause v) Assignment iii) Frm clause. 2) Fr the given emplyee database give an expressin in SQL fr the fllwing. Emplyee (empname, street, city) Wrks (empname, cmpany-name, salary) Cmpany (cmpany-name, City) Manages (empname, manager-name) (i) Create table,instert values fr all the table given (ii) Mdify the database s that jnes nw lives in newtwn (iii) Give all emplyees f first bank crpratin a 10 percent raise. 2) Fr the given database with SQL query: Emplyee (eid, emplyee_name, street, city)

37 Wrks (eid, cid,salary) Cmpany (cid,cmpany_name,and city) Manager (eid,manager_name) i) Find the name, street and city f all emplyee wh wrk fr ABC and mre than rs.200 ii) Find the name f all emplyee having i as the secnd letter in there name. iii) Display the annual salary f all emplyees. 3) Hw many cds rule must a DBMS satisfy t quality f DBMS? 4) Fr the fllwing given database, write a sql query. Persn (driver_id#, name, address) Car (license, mdel, year) Accident (reprt_n, date, lcatin) Owns (driver_id,car,reprt_n,damage_amt) i) Find the ttal number f peple wh wned cars that were invlved in accident in ii) Find the number f accident in which the cars belnging t Sunil K.were invlved. iii) Update damage amunt fr car with license n. Mum2022 In the accident with reprt number AR2197 t Rs ) Give the name f all aggregate functin and explain. 6) Explain the grup by having clause with example. 8) Give the shrt nte with example. A) UNION B) INTERSECTION 4.11 References 1. Micrsft SQL Server 2000 Bible, Wiley. 2. BALTER, MS SQL SERVER 2005 EXPRESS IN 24 Hurs, Pearsn Educatin

38