Structured Query Language: Introduction

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1 Structured Query Language: Introduction

2 Structured Query Language: Intro What is SQL? Relational model s standard language all RDBMS software support SQL many software vendors have developed extensions to basic SQL there are small differences across RDBMS implementations of SQL Non-procedural language user specifies what must be done, not how it is to be done SQL programmers do not need to know the step-by-step task execution details. What can SQL do? Create database & table structures Perform data manipulation & data administration add, modify, delete, retrieve data create tables, indexes, views Query the database to extract useful information Why SQL? de facto standard for RDB ANSI SQL (1986, 1992, 1999) Relatively easy to learn (vocabulary of less than 100 words) Database System 2

3 The SQL Environment ODBC (Open Database Connectivity) A standard database access method API for using SQL queries to access data Enables data access from any application regardless of DBMS independent of programming languages, DBMS, and OS both application and DBMS have to be ODBC-compliant Translates applications data queries into DBMS commands a middle layer (database driver) between application and DBMS ODBC driver Database DBMS DBMS commands Application SQL queries Database System 3

4 SQL: Command Type Data Definition Language (DDL) commands Create, alter and drop tables Typically restricted to DB administrators Data Manipulation Language (DML) commands Update, insert, modify, and query the data Core commands of SQL Data Control Language (DCL) commands Grant/revoke access privileges, store/remove transactions Help the DB administrators to control the database Database System 4

5 SQL: Creating/Deleting Tables CREATE TABLE table_name ( column_name column_characteristics,, CONSTRAINT constraint_name PRIMARY KEY (column_name), FOREIGN KEY (column_name) REFERENCES table_name); define a new table and its columns 1 side table in 1:M relationship (i.e. EMPLOYEE) should be created first data types vary from RDBMS to RDBMS CREATE TABLE tblpilot ( Emp_Num INTEGER NOT NULL, Pil_Hrs NUMBER, Pil_License CHAR(25), Pil_Date DATE, CONSTRAINT index1 PRIMARY KEY(Emp_Num), FOREIGN KEY(Emp_Num) REFERENCES tblemployee); DROP TABLE table_name; DROP TABLE tblpilot; Database System 5

6 SQL: Creating Indexes CREATE INDEX index_name ON table_name(column_names) Create SQL indexes based on selected columns Indexes CREATE INDEX P_CODEX ON PRODUCT(P_CODE); CREATE UNIQUE INDEX P_CODEX ON PRODUCT(P_CODE); CREATE INDEX VENPRODX ON PRODUCT(V_CODE, P_CODE); Improve the efficiency of data search Create indexes on fields used in search DBMS automatically creates a unique index for primary key Database System 6

7 SQL: Modifying Table Data INSERT INTO table_name VALUES (col1_value, col2_value, ); Insert a single row into table INSERT INTO tblemployee VALUES (1, Doe, John, M ); INSERT INTO tblemployee VALUES (2, Dew, Jane, NULL); INSERT INTO tblemployee(emp_num, Emp_Fname) VALUES (3, Jim ); INSERT INTO table_name SELECT column_names FROM table_name WHERE condition; Insert multiple rows into table INSERT INTO tblemployee (Emp_Fname, Emp_Lname, Emp_Init) SELECT (App_Fname, App_Lname, App_Init) FROM tblapplicant WHERE App_Hire=1; UPDATE table_names SET column_name=value WHERE condition; Change column values UPDATE tblemployee SET Emp_Lname= Dew, Emp_Status= M WHERE Emp_Num=3; DELETE FROM table_name WHERE condition; Delete table rows DELETE FROM tblemployee WHERE Emp_Num=3; Database System 7

8 SQL: Altering Tables ALTER TABLE table_name ADD column_name column_characteristics; Add column to a table ALTER TABLE tblproduct ADD P_Salescode CHAR(1); ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY(column_name) REFERENCES table_name; Designate a foreign key to a table ALTER TABLE tblproduct ADD CONSTRAINT pk1 FOREIGN KEY(SUP_Num) REFERENCES tblsupplier; ALTER TABLE table_name ALTER column_name column_characteristics; Change column characteristics ALTER TABLE tblproduct ALTER P_Salescode CHAR(10); ALTER TABLE table_name DROP column_name; Drop column from a table ALTER TABLE tblproduct DROP P_Salescode; Database System 8

9 SQL: Copying Table Data 1. Create the new table whose column characteristics match the original table 2. Copy desired table columns and rows into the new table 3. Designate primary and foreign keys if needed CREATE TABLE tbretiree ( Emp_Num INTEGER NOT NULL, Retire_Date DATE, CONSTRAINT pk1 PRIMARY KEY(Emp_Num)); INSERT INTO tblretiree(emp_num, Retire_Date) SELECT (Emp_Num, Hire_Date+3650) FROM tblemployee WHERE (Hire_Date ) Date() < 30; ALTER TABLE tblretiree ADD CONSTRAINT fk1 FOREIGN KEY (Emp_Num) REFERENCES tblemployee; Database System 9

10 SQL: Queries SELECT column_names FROM table_name WHERE condition; Retrieve table rows that match the target criteria Examples SELECT Emp_Num, Emp_Lname FROM tblemployee; SELECT * FROM tblemployee WHERE Emp_status= M ; SELECT P_Onhand*P_Price AS TotalValue FROM tblproduct WHERE P_ID=1234 ; Database System 10

11 Mathematical Operators + - * / ^ Comparison Operators = < <= > >= <> (!=) Logical Operators AND, OR, NOT Special Operators BETWEEN, IS NULL, LIKE, IN, EXISTS Wild Cards % (*) _ (?) Precedence & Case Sensitivity differs across DBMS/platform SQL: Where Clause WHERE P_ID NOT 1234; WHERE P_Price BETWEEN AND ; WHERE Emp_Status IS NULL; WHERE (Emp_Lname LIKE Smith% ) AND (Emp_Status IN ( M, D )); WHERE Emp_Status EXISTS; Database System 11

12 SQL: Aggregate Functions COUNT Number of rows containing not null values in the given column SELECT COUNT(DISTINCT V_code) FROM tblproduct WHERE P_Price < 10.00; MIN/MAX Minimum/maximum value in the given column SELECT * FROM tblproduct WHERE P_Price = (SELECT MAX(P_Price) FROM tblproduct); SUM Sum of all values for the given column SELECT SUM(P_Onhand*P_Price) FROM tbleproduct; AVG Mean value of the given column SELECT * FROM tblproduct WHERE P_Price > (SELECT AVG(P_Price) FROM tblproduct); Database System 12

13 SQL: Sorting & Grouping ORDER BY column_names DESC Sort the list (result of SELECT) by column values Must be the last clause in the command sequence SELECT Emp_Lname, Emp_Fname, Emp_Init, Emp_Phone FROM tblemployee ORDER BY Emp_Lname, Emp_Fname, Emp_Init; GROUP BY column_names HAVING condition; Aggregate column values by group column values Must be used with aggregate function HAVING condition is applied to the output of GROUP BY SELECT SUM(P_Onhand*P_Price) FROM tbleproduct GROUP BY V_Code HAVING AVG(P_Price) < 10; SELECT DISTINCT column_name FROM table_name; List only the unique column values SELECT DISTINCT V_code FROM tblproduct; Database System 13

14 SQL: Joining Tables Natural Join SELECT column_names FROM table1_name INNER JOIN table2_name ON table1.column = table2.column; SELECT tblproduct.p_name, tblproduct.p_price, tblvendor.v_name FROM tblproduct INNER JOIN tblvendor ON tblproduct.v_code = tblvendor.v_code; Left Outer Join SELECT column_names FROM table1_name LEFT JOIN table2_name ON table1.column = table2.column; Right Outer Join SELECT column_names FROM table1_name RIGHT JOIN table2_name ON table1.column = table2.column; Database System 14

Introduction to SQL. From Rob and Coronel (2004), Database Systems: Design, Implementation, and Management

Introduction to SQL. From Rob and Coronel (2004), Database Systems: Design, Implementation, and Management Introduction to SQL Introduction to SQL Language to communicate with database! SQL is relatively easy to learn Basic command set has a vocabulary of less than 100 words Nonprocedural language American