Delta & Pine Land Company

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1 SQL? SQL (pronounced "ess-que-el") el") stands for Structured Query Language. A RDB language is used to communicate with a database. ANSI - SQL is the standard language for RDBMS such as Oracle, Sybase, Microsoft SQL Server, Ingres. RDBMS contains schemas Collection of related objects (tables, views, triggers, indexes etc). SQL a non-procedural language: Can be executed without being called in procedures. (dynamic SQL can be called in.net, Java, PHP etc) Executed in two distinct ways- Interactive and programmatic Interactive -> Command Line Interpreter- SQL Engine Programmatic-> Host Language-Embedded SQL-Compiler Benefits of a Standardized Relational Language Reduced training costs Productivity Application portability and longevity. Reduced dependence on a single vendor Cross-system system communication Disadvantages of a standardized relational language stifle creativity and innovation never enough to meet all needs offspring of compromises using special features may result in loss of portability SQL Categories Data Definition Language (DDL): Commands that define a database, including creating, altering, and dropping tables and establishing constraints. Data Manipulation Language (DML) Commands that maintain and query a database. Data Control Language (DCL) Commands that control a database, including administering privileges and committing data. Common SQL Commands Data Definition Language (DDL): Create Drop Alter Rename Querying a Database with SQL SQL statement is entered SQL> SELECT loc Statement is sent to database Data Manipulation Language (DML): Select Update Insert Delete Data Control Language (DCL): Grant Revoke Data is displayed LOC NEW YORK DALLAS CHICAGO BOSTON Database 11/25/97 1

2 Writing SQL Statements SQL statements are not case sensitive (but criteria within quotation marks are) SQL statements can be on one or more lines Clauses are usually placed on separate lines Keywords cannot be split across lines Tabs and spaces are allowed to enhance readability Each SQL statement (not line) ends with a semicolon (;) Data Definition Language (DDL) to Create Tables Identify appropriate datatypes Identify columns that should accept null values Identify columns that need to be unique Identify all PK/FK Determine any default values to be inserted Identify columns which need a domain specification Create the table DDL example in SQL CREATE TABLE ORDER (Order_Id Order_Date Customer_Id char date char not null, default sysdate, not null, primary key (order_id), Constraint Order_pk primary key ( Constraint Order_fk foreign key (Customer_Id) references Customer(Customer_Id)); Cust_ID Customer Order Order_ID Order_Date Data Manipulation Language (DML) This is the major focus of our coverage of SQL Most useful for querying database based on specific criteria Includes: insert, delete, update, and select Base table :A table in the relational data model containing inserted raw data that is likely to correspond to one physical file in secondary storage. View. A view is a virtual table and is often part of an external database. In contrast to a defined base table (relation), a view is not permanently represented in storage. A view definition is stored, and the contents of the view are calculated each time the view is referenced in a query. A view may join multiple tables or views together and may contain derived (or virtual) columns, while base tables cannot. In comparison to a temporary real table, a view consumes very little storage space. DML - Inserting Useful for populating a database Syntax is: INSERT INTO Product(Product_ID, Product _Name, Unit_Price, On_Hand) VALUES (1, End Table, 175, 8); Or INSERT INTO Ca_Customer SELECT * FROM Customer WHERE State= CA ; 11/25/97 2

3 DML - Deleting DELETE FROM Customer WHERE State= HI ; Or DELETE FROM Customer; UPDATE Product DML - Updating SET Unit_Price = 775 WHERE Product_ID = 7; DML - SELECT Statement Syntax: SELECT [DISTINCT] column_list FROM table_list [WHERE conditional expression] [GROUP BY column_list] [HAVING conditional expression] [ORDER BY column_list] ; SELECT statement processing order The Basic SELECT Statement SELECT column1, column2, column3,... FROM table; SELECT identifies what columns FROM identifies which table 11/25/97 3

4 Example SELECT Statement? SQL> SELECT deptno, loc SQL> SELECT * DEPTNO LOC NEW YORK 20 DALLAS 30 CHICAGO 40 BOSTON DEPTNO DNAME LOC ACCOUNTING NEW YORK 20 RESEARCH DALLAS 30 SALES CHICAGO 40 OPERATIONS BOSTON Specifying Output Headings Specifying Output Headings SQL> SELECT loc AS location SQL> SELECT loc AS Location Double quotes LOCATION NEW YORK DALLAS CHICAGO BOSTON Note Upper-Case Heading Location NEW YORK DALLAS CHICAGO BOSTON Note Mixed-Case Heading Duplicate Output Suppressing Duplicate Output SQL> SELECT job ; SQL> SELECT DISTINCT job ; JOB PRESIDENT MANAGER MANAGER MANAGER SALESMAN SALESMAN... Total records displayed JOB ANALYST CLERK MANAGER PRESIDENT SALESMAN Each unique job is listed only once 11/25/97 4

5 Limiting Rows with WHERE SQL> SELECT ename, job, sal 3 WHERE job = CLERK ; ENAME JOB SAL JAMES CLERK 950 SMITH CLERK 800 ADAMS CLERK 1100 MILLER CLERK 1300 Case sensitive; single quotes WHERE Clause Criteria Text and dates (sometimes) are enclosed in single quotes Numbers are not enclosed in quotes Text values are case sensitive Date values are format sensitive Oracle s default date format is DD-MM MM-YY, SQL> SELECT ename, hiredate 3 WHERE hiredate >= 01-Jan-2007'; SQL Comparison Operators SQL Comparison Operators OPERATOR MEANING = Equal to > Greater than >= Greater than or equal to < Less than <= Less than or equal to <> or!= Not equal to OPERATOR BETWEEN... AND... IN(list) LIKE IS NULL MEANING Is between the values specified (inclusive) Is in a list of values specified Matches a pattern (may include wildcards) Is a null value BETWEEN Operator Example IN Operator Example SQL> SELECT ename, sal 3 WHERE sal BETWEEN 1000 AND 1500; SQL> SELECT ename, job 3 WHERE job IN( PRESIDENT, MANAGER ); ENAME SAL MARTIN 1250 TURNER 1500 WARD 1250 ADAMS 1100 MILLER 1300 ENAME JOB KING PRESIDENT BLAKE MANAGER CLARK MANAGER JONES MANAGER 11/25/97 5

6 MySQL Screen Shots 11/25/97 6

7 LIKE Operator Example SQL> SELECT ename 3 WHERE ename LIKE J% ; ENAME JONES JAMES The % is a wildcard character that stands for zero to many characters. The underscore character (_) can be used to stand for exactly one character. [ LIKE is not the same as = ] IS NULL Operator Example SQL> SELECT ename, mgr 3 WHERE mgr IS NULL; ENAME MGR KING You cannot use = NULL or!= NULL 11/25/97 7

8 Update studentlist set exam_center = NULL where length(ltrim(rtrim(exam_center))) = ; 11/25/97 8