Structure Query Language (SQL)

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1 Structure Query Language (SQL) 1. Intrductin SQL 2. Data Definitin Language (DDL) 3. Data Manipulatin Language ( DML) 4. Data Cntrl Language (DCL) 1

2 Structured Query Language(SQL) 6.1 Intrductin Structured Query Language (SQL) is a standard cmputer language fr relatinal database management and data manipulatin. SQL is used t query, insert, update and mdify data. Mst relatinal databases supprt SQL, which is an added benefit fr database administratrs (DBAs), as they are ften required t supprt databases acrss several different platfrms. 6.2 What can SQL d? 1. SQL can execute queries against a database. 2. SQL can retrieve data frm a database. 3. SQL can insert recrds in a data base. 4. SQL can update recrds in a database. 5. SQL can delete recrds frm a database. 6. SQL can create new data bases. 7. SQL can create new tables in a database. 8. SQL can create stred prcedures in a database. 9. SQL can create views in a data base. 10. SQL can set permissins n tables, prcedures, and views. 6.3 Database Languages A database system prvides a data definitin language t specify the database schema and a data manipulatin language t express database queries and updates and a data cntrl language t cnfigure security access t relatinal databases. In practice, the data definitin and data manipulatin languages are nt tw separate languages; instead they simply frm parts f a single database language, such as the widely used SQL language. 2

3 6.3.1 Data Definitin Language (DDL) The SQL DDL allws specificatin f nt nly a set f relatins, but als infrmatin abut each relatin, including The schema fr each relatin The dmain f values assciated with each attribute The integrity cnstraints The set f indices t be maintained fr each relatin The security and authrizatin infrmatin fr each relatin The physical strage structure f each relatin n disk Data Definitin Language (DDL): statements are used t define the database structure r schema. Sme examples: CREATE - t create bjects in the database. ALTER - alters the structure f the database. DROP - delete bjects frm the database. TRUNCATE - remve all recrds frm a table, including all spaces allcated fr the recrds are remved. COMMENT - add cmments t the data dictinary. RENAME - rename an bject Data Manipulatin Language(DML) A data-manipulatin language (DML) is a language that enables users t access r manipulate data as rganized by the apprpriate data mdel. Data manipulatin is The retrieval f infrmatin stred in the database The insertin f new infrmatin int the database The deletin f infrmatin frm the database The mdificatin f infrmatin stred in the database There are basically tw types: 3

4 Prcedural DMLs require a user t specify what data are needed and hw t get thse data. Declarative DMLs (als referred t as nnprcedural DMLs) require a user t specify what data are needed withut specifying hw t get thse data. Declarative DMLs are usually easier t learn and use than are prcedural DMLs. Hwever, since a user des nt have t specify hw t get the data, the database system has t figure ut an efficient means f accessing data. The DML cmpnent f the SQL language is nnprcedural. A query is a statement requesting the retrieval f infrmatin. The prtin f a DML that invlves infrmatin retrieval is called a query language. Althugh technically incrrect, it is cmmn practice t use the terms query language and data manipulatin language synnymusly. Data Manipulatin Language (DML) statements are used fr managing data within schema bjects. Sme examples: SELECT - retrieve data frm the a database. INSERT - insert data int a table. UPDATE - updates existing data within a table. DELETE - deletes all recrds frm a table, the space fr the recrds remain. MERGE - UPSERT peratin (insert r update). CALL - call a PL/SQL r Java subprgram. EXPLAIN PLAN - explain access path t data. LOCK TABLE - cntrl cncurrency Data Cntrl Language: Data Cntrl Language (DCL) :statement is a subset f the Structured Query Language (SQL) that allws database administratrs t cnfigure security access t relatinal databases. Sme examples: GRANT - gives user's access privileges t database. REVOKE - withdraw access privileges given with the GRANT cmmand. 4

5 6.4 SQL - Data Types SQL data type is an attribute that specifies type f data f any bject. Each clumn, variable and expressin has related data type in SQL. Yu wuld use these data types while creating yur tables. Yu wuld chse a particular data type fr a table clumn based n yur requirement. The SQL standard supprts a variety f built-in dmain types, including: char(n): A fixed-length character string with user-specified length n. The full frm, character, can be used instead. varchar(n): A variable-length character string with user-specified maximum length n. The full frm, character varying, is equivalent. int: An integer (a finite subset f the integers that is machine dependent). The full frm, integer, is equivalent. smallint: A small integer (a machine-dependent subset f the integer dmain type). numeric(p, d): A fixed-pint number with user-specified precisin. The number cnsists f p digits (plus a sign), and d f the p digits are t the right f the decimal pint. Thus, numeric(3,1) allws 44.5 t be stred exactly, but neither r 0.32 can be stred exactly in a field f this type. real, duble precisin: Flating-pint and duble-precisin flatingpint numbers with machine-dependent precisin. flat(n): A flating-pint number, with precisin f at least n digits. date: A calendar date cntaining a (fur-digit) year, mnth, and day f the mnth. time: The time f day, in hurs, minutes, and secnds. A variant, time(p), can be used t specify the number f fractinal digits fr secnds (the default being 0). It is als pssible t stre time zne infrmatin alng with the time. timestamp: A cmbinatin f date and time. A variant, timestamp(p), can be used t specify the number f fractinal digits fr secnds (the default here being 6). Date and time values can be specified like this: date time 09:30:00 time stamp :29:

6 Dates must be specified in the frmat year fllwed by mnth fllwed by day, as shwn. The secnd's field f time r timestamp can have a fractinal part, as in the timestamp abve. We can use an expressin f the frm caste as t cnvert a character string (r string valued expressin) e t the type t, where t is ne f date, time, r timestamp. The string must be in the apprpriate frmat as illustrated at the beginning f this paragraph. T extract individual fields f a date r time value d, we can use extract (field frm d), where field can be ne f year, mnth, day, hur, minute, r secnd SQL Data Type Quick Reference Hwever, different databases ffer different chices fr the data type definitin. The fllwing table shws sme f the cmmn names f data types between the varius database platfrms: Data type Access SQL Server Oracle MySQL PstgreSQL Blean Yes/N Bit Byte N/A Blean Integer Number (integer) Int Number Int Integer Int Integer Flat Number (single) Flat Real Number Flat Numeric Currency Currency Mney N/A N/A Mney string (fixed) N/A Char Char Char Char string (variable) Text (<256) Mem (65k+) Varchar Varchar Varchar2 Varchar Varchar binary bject OLE Object Mem Binary (fixed up t 8K) Varbinary (<8K) Image (<2GB) Lng Raw Blb Text Binary Varbinary 6

7 Nte: Data types might have different names in different database. And even if the name is the same, the size and ther details may be different! Always check the dcumentatin! 6.5 Data Definitin Language (DDL) cmmand Create Cmmand Create is a DDL cmmand used t create a table r a database Creating a Database T create a database in RDBMS, create cmmand is uses. Fllwing is the Syntax, create database database-name; Example fr Creating Database Create database Test; The abve cmmand will create a database named Test Creating a Table Create cmmand is als used t create a table. We can specify names and data types f varius clumns alng. Fllwing is the Syntax, Create table table-name { clumn-name1 datatype1, clumn-name2 datatype2, clumn-name3 datatype3, clumn-name4 datatype4 }; Create table cmmand will tell the database system t create a new table with given table name and clumn infrmatin. 7

8 Example fr creating Table Create table Student(id int, name varchar, age int); The abve cmmand will create a new table Student in database system with 3 clumns, namely id, name and age Alter cmmand Alter cmmand is used fr alteratin f table structures. There are varius uses f alter cmmand, such as, t add a clumn t existing table t rename any existing clumn t change data type f any clumn r t mdify its size. Alter is als used t drp a clumn T Add Clumn t existing Table Using alter cmmand we can add a clumn t an existing table. Fllwing is the Syntax, Alter table table-name add(clumn-name datatype); Here is an Example fr this, alter table Student add(address char); The abve cmmand will add a new clumn address t the Student table T Add Multiple Clumn t existing Table Using alter cmmand we can even add multiple clumns t an existing table. Fllwing is the Syntax, Alter table table-name add(clumn-name1 datatype1, clumn-name2 d atatype2, clumn-name3 datatype3); Here is an Example fr this, alter table Student add(father-name varchar( 60), mther-name varchar(60), db date); 8

9 The abve cmmand will add three new clumns t the Student table 9

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