Lecture Database management systems Chapter 8 SQL

Lecture Database management systems Chapter 8 SQL. SQL commands can be classified in to three types Data Definition Language commands (DDL), Data Manipulation Language commands (DML), Data Control Language commands (DCL).

SQL

Introduction

 SQL commands can be classified in to three types:

 Data Definition Language commands (DDL)

 Data Manipulation Language commands (DML)

 Data Control Language commands (DCL)

user- real, double precision. Floating point and precision floating point numbers, with machine- dependent precision

double- float(n). Floating point number, with user-specified precision of at least n digits

Domain types

 String:

 char(n) Fixed length character string, with

user-specified length n.

 varchar(n) Variable length character

strings, with user-specified maximum length n

 nvarchar(n) similar to varchar, except it

uses Unicode and therefore doubles the amount of space required to store the data

 Text: holds data that is longer than 8,000 characters

Domain types

 Datetime:

 datetime store not only a date, but also a

time alongside it

 smalldatetime

Create Table Construct

 An SQL relation is defined using the create table command:

 r is the name of the relation

 each Ai is an attribute name in the schema of relation r

 Di is the data type of values in the domain of attribute Ai

create table r

(A1 D1, A2 D2, , A n D n , (integrity-constraint1), ,

(integrity-constraintk))

Create Table Construct

 Primary key: dept_no

 Candidate key: dept_name

 CREATE TABLE department

(

dept_no char(3) primary key, dept_name varchar(36) unique not null, location varchar(20)

)

Truncate table

 The TRUNCATE TABLE command removes all the rows from the table The truncate table also releases the storage space used

by the table

 The syntax of TRUNCATE command is:

 TRUNCATE TABLE tablename

Alias

 Tables listed in the FROM clause can be given an

alternative name

 An alias is created by:

 Typing the name of the table

 Pressing the space bar

 Typing the name of the alias

 One reason for using an alias is simplicity

 A second reason for using an alias is that it is needed

when joining a table to itself, called a self-join

Data Manipulation Language

 Adding a New Row to the Table

INSERT INTO tablename

VALUES ( 'value1' , 'value2' , , 'valuen' )

 Updating the Data in the Table

UPDATE table name

WHERE condition ;

 Deleting Row from the Table

DELETE FROM table name

WHERE condition ;

Operators

 Comparison operators (=, <, <=, <>, and so on)

 String comparisons (LIKE, NOT LIKE)

 Logical operators (AND, OR, NOT)

 Ranges (BETWEEN and NOT BETWEEN)

 Lists of values (IN and NOT IN)

 Unknown Values (IS NULL and IS NOT NULL)

 Exists in Subquery (EXISTS and NOT EXISTS)

 Use DISTINCT to eliminate duplicates

 [ TOP (expression ) [PERCENT] [ WITH TIES ] ]

SELECT statement

 The SQL syntax to see all the columns of the table is:

SELECT * FROM table name

 Syntax of SELECTION Operation:

SELECT * FROM table name

WHERE condition;

 Syntax of PROJECTION Operation

SELECT column name1, column name2, Column name N

FROM table name

 Syntax for SELECTION and PROJECTION

SELECT column name1, column name 2 column nameN

FROM table name

WHERE condition;

DATEPART(YY,getda te())

- DATEDIFF(X,Y,Z)

- DAY(),MONTH(),YE AR()

SELECT data

 SELECT * FROM DANHMUCSACH

SELECT - COUNT

 COUNT (*) Function:

 return the number of rows of the relation

Command will take NULL values into account

 COUNT (DISTINCT attribute_name):

 Return the number of Rows of the relation, by eliminating duplicate values

SELECT - COUNT

 SELECT COUNT(*) TONGSOSACH

FROM DANHMUCSACH

WHERE MANHOM = 'n001'

MAX, MIN, AVG, and SUM

SELECT MAX (attribute name)

FROM table name;

SELECT MIN (attribute name)

FROM table name;

SELECT AVG (attribute name)

FROM table name;

SELECT - GROUP BY

 The GROUP BY clause is used to group rows to compute group-statistics

 The syntax of GROUP BY command is:

SELECT attribute name, aggregate function FROM table name

GROUP BY attribute name;

 The syntax of HAVING command is:

SELECT attribute name, aggregate function FROM table name

GROUP BY attribute name

HAVING condition;

SELECT - SORTING

 The SQL command ORDER BY is used to sort the result in ascending or descending order

 The syntax of ORDER BY command to

arrange the result in ascending/

descending order is:

SELECT *

FROM table name

ORDER BY attribute name ASC/ DESC;

SELECT - SORTING

 SELECT * FROM NHANVIEN

ORDER BY TENNV

Join Types

 JOIN or INNER JOIN

 Each row in table to left will be joined with one or more rows in table to right

 Any rows in left table that do not have

corresponding rows in the right table will not

be in the result table

 LEFT JOIN or LEFT OUTER JOIN

 Any rows in left table that do not have

corresponding rows in the right table will be

in the result table with null values for fields from the right table

Join Types

 RIGHT OUTER JOIN

 Keeps stray rows from the right table, filling columns from the left table with NULL values

if no corresponding data

Join Types

 SELECT MAHD , D MASACH , SOLUONG

FROM CHITIETHOADON CT JOIN DANHMUCSACH

DM

ON D MASACH = C MASACH

OR

 SELECT MAHD , D MASACH , SOLUONG

FROM CHITIETHOADON CT, DANHMUCSACH DM WHERE CT MASACH = DM MASACH

Set Operations

 UNION Operation

 If we have two relations R and S then the set

UNION operation contains tuples that either

STORE PROCEDURE

 A stored procedure is a group of SQL statements that is compiled one time, and then can be executed many times

Transact- This increases performance when the

stored procedure is executed because the Transact-SQL statements do not have to

be recompiled

STORE PROCEDURE

STORE PROCEDURE

 Execute store procedure

EXECUTE ProductName [<parameter>[, …n][ OUTPUT ]]

 Ex: EXECUTE PTBACNHAT 1,2

STORE PROCEDURE

 CREATE PROC PTBACNHAT

AS IF(@A=0) BEGIN

IF(@B=0) BEGIN

PRINT 'PHUONG TRINH VO SO NGHIEM' END

ELSE BEGIN

PRINT 'PHUONG TRINH VO NGHIEM' END

END

ELSE BEGIN

PRINT 'NGHIEM PT = '+ CAST((-@B*1.0/@A)AS CHAR) END