Indexes (continued) Customer table with record numbers. Source: Concepts of Database Management

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1 12 Advanced Topics

2 Objectives Use indexes to improve database performance Examine the security features of a DBMS Discuss entity, referential, and legal-values integrity Make changes to the structure of a relational database Define and use the system catalog Discuss stored procedures and triggers 2

3 Indexes Conceptually similar to book index Increase data retrieval efficiency Record numbers automatically assigned and used by DBMS Index key: field or combination of fields on which index is built Advantages Makes some data retrieval more efficient Disadvantages Occupies space on disk DBMS must update index whenever corresponding data are updated 3

4 Indexes (continued) Customer table with record numbers Source: Concepts of Database Management 4

5 Indexes (continued) ROWNUM pseudocolumn in Oracle Index for the Customer table on the CustomerNum field Source: Concepts of Database Management 5

6 B-Tree Index 6

7 B*-tree index 7

8 Bitmap index CREATE BITMAP INDEX Parts_color_idx ON Parts (color); 8

9 Indexes (continued) Create an index on a field (or fields) when: Field is the primary key of the table Field is the foreign key in a relationship Field will be frequently used as a sort field Need to frequently locate a record based on a value in this field SQL command to create an index: CREATE INDEX CustomerName_idx ON Customer (CustomerName); Guidelines to creating an index Do not create an index if The table is small The columns are not often used as a condition in a query Most queries are expected to retrieve more than 2~4% of the rows The table is updated frequently 9

10 CREATE INDEX Command Examples Single-field index Key is a single field Also called a single-column index Multiple-field index More than one key field Also called a multiple-column index Source: A Guide to SQL 10

11 Function-Based Indexes Index Organized Tables An IOT stores table contents in a B-tree index structure Use the ORGANIZATION INDEX option in a CREATE TABLE statement to build an IOT 11

12 Verifying an Index Use the USER_INDEXES data dictionary view to determine that the index exists Use the USER_IND_COLUMNS data dictionary view to determine the column index information Source: A Guide to SQL 12

13 USER_IND_COLUMNS Source: A Guide to SQL 13

14 Removing an Index Use the DROP INDEX command to remove an index Source: A Guide to SQL 14

15 Security Prevention of unauthorized access to database Database administrator determines types of access various users can have SQL security mechanisms GRANT: provides privileges to users GRANT SELECT ON Customer TO Jones ; REVOKE: removes privileges from users REVOKE SELECT ON Customer FROM Jones ; 15

16 Integrity Rules Two integrity rules must be enforced by a relational DBMS Integrity rules defined by Dr. E.F. Codd Entity integrity Referential integrity 16

17 Entity Integrity No field that is part of primary key may accept null values To specify primary key in SQL: Enter a PRIMARY KEY clause in either an ALTER TABLE or a CREATE TABLE command SQL command to specify a primary key: PRIMARY KEY (CustomerNum) SQL command when more than one field included: PRIMARY KEY (OrderNum, PartNum) 17

18 Referential Integrity Foreign key: field(s) whose value is required to match the value of the primary key for a second table Referential integrity: if table A contains a foreign key that matches the primary key of table B, the values of this foreign key must match the value of the primary key for some row in table B or be null To specify referential integrity in SQL: FOREIGN KEY clause in either the CREATE TABLE or ALTER TABLE commands To specify a foreign key, must specify both: Field that is a foreign key Table whose primary key the field is to match Example: FOREIGN KEY (RepNum) REFERENCES Rep(RepNum) 18

19 Legal-Values Integrity Legal values: set of values allowable in a field Legal-values integrity: no record can exist with a value in the field other than one of the legal values SQL CHECK clause enforces legal-values integrity Example: CHECK (CreditLimit IN (5000, 7500, 10000, 15000)) 19

20 Constraints Rules used to enforce business rules, practices, and policies Rules used to ensure accuracy and integrity of data Source: A Guide to SQL 20

21 Creating Constraints Use the optional CONSTRAINT keyword during creation to assign a name Let the server name the constraint using the default format SYS_Cn Informative names can assist in debugging When During table creation After table creation, by modifying the existing table How Column level approach Table level approach 21

22 Creating Constraints at the Column Level If a constraint is being created at the column level, the constraint applies to the column specified at the Table Level Approach can be used to create any constraint type except NOT NULL Required if constraint is based on multiple columns Enforcement of Constraints All constraints are enforced at the table level If a data value violates a constraint, the entire row is rejected 22

23 Including Constraints during Table Creation Column Level Include in column definition Table Level Include at end of column list 23

24 Multiple Constraints on a Single Column A column may be included in multiple constraints The order# column is included in a primary key and a foreign key constraint 24

25 Structure Changes Examples of changes to database structure Adding and removing tables and fields Changing characteristics of existing fields Creating and dropping indexes SQL ALTER TABLE command changes table s structure To add a new field to the Customer table: ALTER TABLE Customer ADD CustType CHAR(1); Changing properties of existing fields ALTER TABLE Customer CHANGE COLUMN CustomerName TO CHAR(40); Deleting a field from a table ALTER TABLE Part DELETE Warehouse; DROP TABLE command deletes a table DROP TABLE SmallCust; 25

26 Making Complex Changes Some changes might not be allowed by your DBMS In these situations, you can: Use CREATE TABLE command to describe the new table Insert values into it using INSERT command combined with a SELECT clause INSERT INTO emp_log SELECT * FROM emp WHERE empno = 7900; SELECT INTO command can create the new table in a single operation works in mysql only, not in Oracle SELECT * INTO backup_orders -- new table name FROM orders; -- source table name SELECT order_num, order_date INTO backup_orders FROM orders; -- source table name 26

27 Adding Constraints to Existing Tables Constraints are added to an existing table with the ALTER TABLE command Add a NOT NULL constraint using MODIFY clause All other constraints are added using ADD clause Using the PRIMARY KEY Constraint Ensures that columns do not contain duplicate or NULL values Only one per table is allowed PRIMARY KEY Constraint for Composite Key List column names within parentheses separated by commas Source: A Guide to SQL 27

28 Constraint Checked with Data Input Source: A Guide to SQL 28

29 Using the FOREIGN KEY Constraint Requires a value to exist in the referenced column of another table NULL values are allowed Enforces referential integrity Maps to the PRIMARY KEY in parent table Source: A Guide to SQL 29

30 Deletion of Foreign Key Values You cannot delete a value in a parent table referenced by a row in a child table: default ON DELETE RESTRICT or ON DELETE NO ACTION ON DELETE CASCADE keywords when creating FOREIGN KEY constraint it automatically deletes the dependent rows in the child table when a row in the parent table is deleted CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ); CREATE TABLE child ( id INT, parent_id INT, INDEX par_ind (parent_id), FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE CASCADE ) ; 30

31 Deletion of Foreign Key Values CREATE TABLE customer ( customer_id INT NOT NULL, PRIMARY KEY (id) ); CREATE TABLE orders ( order_no INT NOT NULL, order_date DATE NOT NULL, customer_id INT NOT NULL, PRIMARY KEY(order_no) ); ON DELETE SET NULL ALTER TABLE orders ADD CONSTRAINT orders_customer_fk FOREIGN KEY (customer_id) REFERENCES customer(customer_id) ON DELETE SET NULL; ON DELETE SET DEFAULT Assume the column has the default value ALTER TABLE emp ADD CONSTRAINT emp_dept_fk FOREIGN KEY (dept_id) REFERENCES dept(dept_id) ON DELETE SET DEFAULT; 31

32 Using the UNIQUE Constraint No duplicates are allowed in the referenced column NULL values are permitted Source: A Guide to SQL 32

33 Using the CHECK Constraint Updates and additions must meet specified condition Source: A Guide to SQL 33

34 Using the NOT NULL Constraint The NOT NULL constraint is a special CHECK constraint with IS NOT NULL condition Can only be created at column level Included in output of DESCRIBE command Can only be added to an existing table using ALTER TABLE MODIFY command Source: A Guide to SQL 34

35 Using DISABLE/ENABLE Use DISABLE or ENABLE clause of ALTER TABLE command 35

36 Dropping Constraints Constraints cannot be modified; must be dropped and recreated Actual syntax depends on type of constraint PRIMARY KEY just list type of constraint UNIQUE include column name All others reference constraint name Source: A Guide to SQL 36

37 Drop Constraint Example Error Source: A Guide to SQL 37

38 System Catalog/Data Dictionary System catalog (or catalog) Contains information about tables in the database Maintained automatically by DBMS Example catalog has two tables Systables: information about the tables known to SQL Syscolumns: information about the columns within these tables Other possible tables Sysindexes: information about indexes Sysviews: information about views used to determine information about the structure of the DB Documenter: allows user to print detailed documentation about any table, query, report, form, or other object in the database Oracle uses SHOW DBA_TABLES, SHOW DBA_TAB_COLUMNS, and SHOW DBA_VIEWS commands 38

39 Viewing Constraints USER_CONSTRAINTS Display constraint listing for a specific table Source: A Guide to SQL 39

40 Viewing Constraints USER_CONS_COLUMNS Display constraint listing by column Source: A Guide to SQL 40

41 Client/server system Stored Procedures Database resides on a computer called the server Users access database through clients Client Computer connected to a network Has access through server to the database Stored procedure Special file used to store a query that is run often Placed on the server Improves overall performance Convenience 41

42 MySQL Stored Procedures (continued) Delimiter: semicolon at the end of a MySQL command Need to temporarily change the delimiter for a stored procedure To use a stored procedure: CALL followed by the procedure name Access does not support stored procedures Use a parameter query instead 42

43 Stored Procedures (Oracle) 43

44 Stored Procedures (Oracle) 44

45 Stored Procedures Logic 45

46 Stored Procedures (Oracle) CREATE OR REPLACE Procedure p_dept_insert ( v_deptno in number, v_dname in varchar2, v_loc in varchar2, v_result out varchar2) IS cnt number := 0; BEGIN SELECT COUNT(*) INTO CNT FROM DEPT WHERE DEPTNO = v_deptno AND ROWNUM = 1; if cnt > 0 then v_result := ' 이미등록된부서번호이다 '; else INSERT INTO DEPT (DEPTNO, DNAME, LOC) VALUES (v_deptno, v_dname, v_loc); COMMIT; v_result := ' 입력완료!!'; end if; EXCEPTION WHEN OTHERS THEN ROLLBACK; v_result := 'ERROR 발생 '; END; 46

47 Triggers Action that occurs automatically in response to an associated database operation such as an INSERT, UPDATE, or DELETE command Stored and compiled on the server Need to temporarily change the delimiter Access does not support triggers Access 2010 has data macros that have similar functionality 47

48 Triggers (Oracle) Oracle CREATE TABLE ORDER_LIST ( ORDER_DATE CHAR(8) NOT NULL, PRODUCT VARCHAR2(10) NOT NULL, QTY NUMBER NOT NULL, AMOUNT NUMBER NOT NULL); CREATE TABLE SALES_PER_DATE ( SALE_DATE CHAR(8) NOT NULL, PRODUCT VARCHAR2(10) NOT NULL, QTY NUMBER NOT NULL, AMOUNT NUMBER NOT NULL); 48

49 Triggers (Oracle) CREATE OR REPLACE Trigger SUMMARY_SALES AFTER INSERT ON ORDER_LIST FOR EACH ROW DECLARE o_date ORDER_LIST.order_date%TYPE; o_prod ORDER_LIST.product%TYPE; BEGIN o_date := :NEW.order_date; o_prod := :NEW.product; UPDATE SALES_PER_DATE SET qty = qty + :NEW.qty, amount = amount + :NEW.amount WHERE sale_date = o_date AND product = o_prod; if SQL%NOTFOUND then INSERT INTO SALES_PER_DATE VALUES (o_date, o_prod, :NEW.qty, :NEW.amount); end if; END; 49

50 Procedure 와 Trigger 의차이점 50

51 Summary Indexes facilitate data retrieval from the database Security is provided in SQL systems using the GRANT and REVOKE commands Entity integrity: no field that is part of the primary key can accept null values Referential integrity: value in any foreign key field must be null or must match an actual value in the primary key field of another table Legal-values integrity: value entered in a field must be one of the legal values that satisfies some particular condition 51

52 Summary (continued) ALTER TABLE command allows you to add fields to a table, delete fields, or change the characteristics of fields DROP TABLE command lets you delete a table from a database System catalog stores information about the structure of a database Stored procedure: query saved in a file that users can execute later Trigger: action that occurs automatically in response to an associated database operation such as an INSERT, UPDATE, or DELETE 52