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Structured Query Language

Structured Query Language. S tructured Q uery L anguage : 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

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Structured Query Language

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  1. Structured Query Language S511 Session 10, IU-SLIS

  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) S511 Session 10, IU-SLIS

  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 ODBCdriver DBMS Application Database DBMScommands SQL queries S511 Session 10, IU-SLIS

  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 S511 Session 10, IU-SLIS

  5. SQL: Creating/Deleting Tables • CREATE TABLE table_name ( column_name column_characteristics, …,CONSTRAINT constraint_namePRIMARY 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; S511 Session 10, IU-SLIS

  6. SQL: Creating Indexes • CREATE INDEX index_nameON table_name(column_names) • Create SQL indexes based on selected columns • CREATE INDEX P_CODEXON PRODUCT(P_CODE); • CREATEUNIQUEINDEX P_CODEXON PRODUCT(P_CODE); • CREATE INDEX VENPRODX ON PRODUCT(V_CODE, P_CODE); • Indexes • Improve the efficiency of data search • Create indexes on fields used in search • DBMS automatically creates a unique index for primary key S511 Session 10, IU-SLIS

  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 SELECTcolumn_names FROM table_name WHERE condition; • Insert multiple rows into table INSERT INTO tblEmployee (Emp_Num, Emp_Fname, Emp_Lname, Emp_Init) SELECT App_Hire, App_Fname, App_Lname, App_Init FROM tblApplicant WHERE App_Hire=4; • UPDATE table_names SET column_name=value WHERE condition; • Change column values • UPDATE tblEMPLOYEESET 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; S511 Session 10, IU-SLIS

  8. SQL: Altering Tables • ALTER TABLE table_nameADD column_name column_characteristics; • Add column to a table • ALTER TABLE tblProductADD P_Salescode CHAR(1); • ALTER TABLE table_nameADD CONSTRAINT constraint_name FOREIGN KEY(column_name) REFERENCES table_name; • Designate a foreign key to a table • ALTER TABLE tblProductADDCONSTRAINT pk1 FOREIGN KEY(SUP_Num) REFERENCES tblSupplier; • ALTER TABLE table_nameALTER column_name column_characteristics; • Change column characteristics • ALTER TABLE tblProductALTER P_Salescode CHAR(10); • ALTER TABLE table_nameDROP column_name; • Drop column from a table • ALTER TABLE tblProductDROP P_Salescode; S511 Session 10, IU-SLIS

  9. SQL: Copying Table Data • Create the new table whose column characteristics match the original table • Copy desired table columns and rows into the new table • 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 tblEmployeeWHERE (Hire_Date + 3650) – Date() < 30; ALTER TABLE tblRetireeADDCONSTRAINT fk1FOREIGN KEY (Emp_Num) REFERENCES tblEmployee; S511 Session 10, IU-SLIS

  10. SQL: Queries • SELECT column_names FROM table_name WHERE condition; • Retrieve table rows that match the target criteria • ExamplesSELECT Emp_Num, Emp_Lname FROM tblEmployee;SELECT * FROM tblEmployee WHERE Emp_Num=1;SELECT P_Onhand*P_Price AS TotalValue FROM tblProduct WHERE P_Code=1; S511 Session 10, IU-SLIS

  11. SQL: Where Clause • 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 • WHERE P_ID NOT 1234; • WHERE P_Price BETWEEN 50.00 AND 100.00; • WHERE Emp_Status IS NULL; • WHERE (Emp_Lname LIKE ‘Smith%’) AND (Emp_Status IN (‘M’,‘D’)); • WHERE Emp_Status EXISTS; S511 Session 10, IU-SLIS

  12. SQL: Aggregate Functions • COUNT • Number of rows containing not null values in the given column • SELECT DISTINCT (V_code) FROM tblProductWHERE P_Price < 10.00; • MIN/MAX • Minimum/maximum value in the given column • SELECT * FROM tblProductWHERE P_Price = (SELECT MAX(P_Price) FROM tblProduct); • SUM • Sum of all values for the given column • SELECT SUM(P_Onhand*P_Price) FROM tblProduct; • AVG • Mean value of the given column • SELECT * FROM tblProductWHERE P_Price > (SELECT AVG(P_Price) FROM tblProduct); S511 Session 10, IU-SLIS

  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_InitFROM tblEmployeeORDER BY Emp_Lname, Emp_Fname, Emp_Init; • GROUP BY column_namesHAVING condition; • Aggregate column values by group column values • Must be used with aggregate function • HAVING condition is applied to the output of GROUP BY • SELECTSUM(P_Onhand*P_Price) FROM tblProduct GROUP BY V_CodeHAVING AVG(P_Price) > 1; • SELECT DISTINCT column_name FROM table_name; • List only the unique column values • SELECT DISTINCT V_code FROM tblProduct; S511 Session 10, IU-SLIS

  14. SQL: Joining Tables • Natural Join • SELECT column_namesFROM table1_name INNER JOIN table2_name ON table1.column = table2.column; SELECT tblProduct.P_Code, tblProduct.P_Price, tblVendor.V_Name FROM tblProduct INNER JOIN tblVendor ON tblProduct.V_Code = tblVendor.V_Code; • Left Outer Join • SELECT column_namesFROM table1_name LEFT JOIN table2_name ON table1.column = table2.column; • Right Outer Join • SELECT column_namesFROM table1_name RIGHT JOIN table2_name ON table1.column = table2.column; S511 Session 10, IU-SLIS

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