1. Week 4 Lecture Part 2 of 3 Structured Query Language (SQL) Samuel ConnSamuel Conn, Faculty Suggestions for using the Lecture Slides

2. 2 In this lecture, you will learn: The basic commands and functions of SQL How SQL is used for data manipulation (to add, modify, delete, and retrieve data) How to use SQL to query a database to extract useful information How SQL is used for data administration (to create tables, indexes, and views) About more advanced SQL features such as updatable views, stored procedures, and triggers

3. 3 Introduction to SQL Ideal database language Create database and table structures Perform basic data management chores (add, delete, and modify) Perform complex queries to transform data into useful information SQL is the ideal DB language Data definition language Data manipulation language

4. 4 Good Reasons to Study SQL ANSI standardization effort led to de facto query standard for relational database Forms basis for present and future DBMS integration efforts Becomes catalyst in development of distributed databases and database client/server architecture

5. 5 Data Definition Commands Create database structure Holds all tables and is a collection of physical files stored on disk DBMS automatically creates tables to store metadata Database administrator creates structure or schema Logical group of tables or logical database Groups tables by owner Enforces security

6. 6 Creating Table Structure Tables store end-user data May be based on data dictionary entries CREATE TABLE ( );

7. 7 Using Domains Domain is set of permissible values for a column Definition requires: Name Data type Default value Domain constraint or condition CREATE DOMAIN AS DATA_TYPE [DEFAULT ] [CHECK ( )]

8. 8 SQL Integrity Constraints Adherence to entity integrity and referential integrity rules is crucial Entity integrity enforced automatically if primary key specified in CREATE TABLE command sequence Referential integrity can be enforced in specification of FOREIGN KEY Other specifications to ensure conditions met: ON DELETE RESTRICT ON UPDATE CASCADE

9. 9 Data Manipulation Commands Common SQL Commands Table 5.3

10. 10 Data Entry and Saving Enters data into a table Saves changes to disk INSERT INTO VALUES (attribute 1 value, attribute 2 value, … etc.); COMMIT ;

11. 11 Listing Table Contents and Other Commands Allows table contents to be listed UPDATE command makes data entry corrections ROLLBACK command restores database back to previous condition if COMMIT hasn’t been used DELETE command removes table row SELECT FROM ;

12. 12 Queries Creating partial listings of table contents SELECT FROM WHERE ; Table 5.4 Mathematical Operators

13. 13 Examples Mathematical operators Mathematical operators on character attributes Mathematical operators on dates SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE FROM PRODUCT WHERE V_CODE <> 21344; SELECT P_CODE,P_DESCRIPT,P_ONHAND,P_MIN,P_PRICE FROM PRODUCT WHERE P_CODE < ‘1558-QWI’; SELECT P_DESCRIPT,P_ONHAND,P_MIN,P_PRICE,PINDATE FROM PRODUCT WHERE P_INDATE >= ‘01/20/2002’;

14. 14 Computed Columns New columns can be created through valid computations or formulas Formulas may contain mathematical operators May contain attributes of any tables specified in FROM clause Alias is alternate name given to table or column in SQL statement SELECT P_DESCRIPT,P_ONHAND,P_PRICE,P_ONHAND*P_PRICE AS TOTVALUE FROM PRODUCT;

15. 15 Operators Logical: AND, OR, NOT Rules of precedence Conditions within parenthesis executed first Boolean algebra Special BETWEEN - defines limits IS NULL - checks for nulls LIKE - checks for similar string IN - checks for value in a set EXISTS - opposite of IS NULL SELECT * FROM PRODUCT WHERE V_CODE = 21344 OR V_CODE = 24288;

16. 16 Advanced Data Management Commands ALTER - changes table structure ADD - adds column MODIFY - changes column characteristics Entering data into new column ALTER TABLE ADD ( ); ALTER TABLE MODIFY ( ); UPDATE PRODUCT SET P_SALECODE = ‘2’ WHERE P_CODE = ‘1546-QQ2’;

17. 17 Advanced Data Management Commands (con’t.) Dropping a column Arithmetic operators and rules of precedence ALTER TABLE VENDOR DROP COLUMN V_ORDER; Table 5.5

18. 18 Advanced Data Management Commands (con’t.) Copying parts of tables Deleting a table from database Primary and foreign key designation INSERT INTO SELECT FROM ; DROP TABLE PART; ALTER TABLE LINE ADD PRIMARY KEY (INV_NUMBER, LINE_NUMBER) ADD FOREIGN KEY (INV_NUMBER) REFERENCES INVOICE ADD FOREIGN KEY (PROD_CODE) REFERENCES PRODUCT;

19. 19 Example Aggregate Function Operations COUNT MAX and MIN SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT; SELECT COUNT(DISTINCT V_CODE) FROM PRODUCT WHERE P_PRICE <= 10.00; SELECT MIN(P_PRICE) FROM PRODUCT; SELECT P_CODE, P_DESCRIPT, P_PRICE FROM PRODUCT WHERE P_PRICE = MAX(P_PRICE);

20. 20 Example Aggregate Function Operations (con’t.) SUM AVG SELECT SUM(P_ONHAND * P_PRICE) FROM PRODUCT; SELECT P_DESCRIPT, P_ONHAND, P_PRICE, V_CODE FROM PRODUCT WHERE P_PRICE > (SELECT AVG(P_PRICE) FROM PRODUCT) ORDER BY P_PRICE DESC;

21. 21 More Complex Queries and SQL Functions Ordering a listing Results ascending by default Descending order uses DESC Cascading order sequence ORDER BY ORDER BY DESC ORDER BY

22. 22 More Complex Queries and SQL Functions (con’t.) Listing unique values DISTINCT clause produces list of different values Aggregate functions Mathematical summaries SELECT DISTINCT V_CODE FROM PRODUCT; Table 5.6

23. 23 More Complex Queries and SQL Functions (con’t.) Grouping data Creates frequency distributions Only valid when used with SQL arithmetic functions HAVING clause operates like WHERE for grouping output SELECT P_SALECODE, MIN(P_PRICE) FROM PRODUCT_2 GROUP BY P_SALECODE; SELECT V_CODE,COUNT(DISTINCT(P_CODE)),AVG(P_PRICE) FROM PRODUCT_2 GROUP BY V_CODE HAVING AVG(P_PRICE) < 10;

24. 24 More Complex Queries and SQL Functions (con’t.) Virtual tables: creating a view CREATE VIEW command Creates logical table existing only in virtual memory SQL indexes CREATE VIEW PRODUCT_3 AS SELECT P_DESCRIPT, P_ONHAND, P_PRICE FROM PRODUCT WHERE P_PRICE > 50.00; CREATE INDEX P_CODEX ON PRODUCT(P_CODE);

25. 25 More Complex Queries and SQL Functions (con’t.) Joining database tables Data are retrieved from more than one table Recursive queries joins a table to itself Outer joins can be used when ‘null’ values need to be included in query result SELECT PRODUCT.P_DESCRIPT, PRODUCT.P_PRICE, VENDOR.V_NAME, VENDOR.V_CONTACT, VENDOR.V_AREACODE, VENDOR.V_PHONE FROM PRODUCT, VENDOR WHERE PRODUCT.V_CODE = VENDOR.V_CODE; SELECT A.EMP_NUM,A.EMP_LNAME,A.EMP_MGR, B.EMP_LNAME FROM EMP A, EMP B WHERE A.EMP_MGR=B.EMP_NUM ORDER BY A.EMP_MGR

26. 26 Updatable Views Common operation in production environments is use of batch routines to update master table attributes using transaction data Overnight batch jobs Not all views are updatable Restrictions GROUP BY expressions cannot be used Cannot use set operators---UNION, INTERSECTION, etc. Most restrictions based on use of JOINS or group operators in views

27. 27 Procedural SQL SQL shortcomings Doesn’t support execution of stored procedures based on logical condition Fails to support looping operations Solutions Embedded SQL can be called from within procedural programming languages Shared Code is isolated and used by all application programs. Procedural SQL (PL/SQL) stored within the database, executed by DBMS, and invoked by the end user Triggers Stored procedures PL/SQL functions

28. 28 Procedural SQL (con’t.) Procedural SQL allows the use of procedural code and SQL statements that are stored within the database. The procedural code is executed by the DBMS when it is invoked by the end user. End users can use procedural SQL (PL/SQL) to create: Triggers Stored procedures PL/SQL functions

29. 29 Triggers Procedural SQL code invoked before or after data row is selected, inserted, or updated Associated with a database table Table may have multiple triggers Executed as part of transaction Can enforce particular constraints Automate critical actions and provide warnings for remedial action Can update values, insert records, and call procedures Add processing power

30. 30 Triggers (con’t.) Oracle example CREATE OR REPLACE TRIGGER [BEFORE/AFTER] [DELETE/INSERT/UPDATE OF <column_name] ON [FOR EACH ROW] BEGIN PL/SQL instructions; …………… END;

31. 31 Stored Procedures Named collection of procedural and SQL statements stored in database Invoked by name Executed as unit Invoked with EXEC CREATE OR REPLACE PROCEDURE procedure_name (argument IN/OUT data-type, etc) IS/AS BEGIN DECLARE variable name and data type PL/SQL or SQL statements; END; EXEC store_procedure_name (parameter, parameter, …)

32. 32 PL/SQL Stored Functions Named group of procedural and SQL statements that returns a value Invoked from within stored procedures or triggers Cannot be invoked from within SQL statements CREATE FUNCTION function_name (argument IN data-type, etc) RETURN data-type AS BEGIN PL/SQL statements; RETURN (value); …… END;