SELECT Statement S2

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Saturday, April 14, 2012 MySQL- DML & DCL 1

Inserting, Updating and

Deleting Records in MySQL

SELECT Statement

@Instructor by Ngo Trung Kien

Date: Thursday, September 09, 2010RDBMS and Data Management




Inserting Records in MySQL

Inserting

Inserting Multiple Rows

Inserting SET

INSERT INTO table_name (List

field,…,) VALUES(Value1,Value2,…,);

INSERT INTO table_name (List field,…,) VALUES

(Value1,Value2,…,), (Value1,Value2,…,),

(Value1,Value2,…,),. . . ;

INSERT INTO table_name

SET Field_1= value_1, Field_2=value_2,…,;




Updating, DELETE Data in MySQL

UPDATE table_name

SET field = value [,field = value]

[WHERE conditions];

DELETE FROM <table_name>

WHERE <conditions>;




Variable in T-SQL

SyntaxLocal

DECLARE{ @local_name [as] Data_type,

@local_name [as] Data_type,...}

local_name: Name of variable data_type: is a data type of system or user define

Example

DECLARE @student_id char[10]

DECLARE @proId int

Global: that are defined and maintained by the sytems.@@VERSION




Comments in SQL

The standard SQL comment is two hyphens (--).However, some databases use other forms of commentsas shown in the table below.




Introduction

The SELECT statement is discussed in order to retrieve andaccess data from database

That data that is retrieved is not only useful for the purpose ofreading but also for modification by operator as UPDATE,DELETE,…

In a table data can be viewed using the SELECT statement willdisplay the required information in table

The SELECT statement retrieves rows and columns from one ormore table

The Ouput of the SELECT statement is another table calledresult set

The columns appear in the same sequence as the order ofexpression in the SELECT statement.




Classifying SELECT statement

The SELECT statement also joins two table,or retrieves a subset of columns from one ormore tables

The SELECT statement also defines thecolums to be used for a query

The SELECT statement can consist of aseries of expressions seperates by commas




Syntax SELECT statement

Syntax:

SELECT <collection>

[FROM <table name>][ WHERE <expression>]

[GROUP BY <expression> HAVING

<Condition>][ORDER BY <Field_name> ASC| DESC]

[LIMIT <[Offset,] Limit>]

Which:

collection: list of column name in any table (include between columns “,” if retrieves than one) or any (function, variable,..) table name: List of tabl

Expression: Operators and comparison




Full SELECT statement




Example SELECT statement

SELECT * FROM tblCategories

SELECT cat_id

,cat_name

,cat_img

FROM tblCategories SELECT c.cat_id as ID

,c.cat_name as category_name

FROM tblCategories as c

WHERE c.cat_id=‘PA001’

SELECT LEFT(‘C0909K’,3)




SELECT INTO

INTO clause creates a new table and insertrows, colums listed in the SELECT

INTO clause inserts existing rows into the

new table SELECT <list colums>

INTO <new table>

FROM <table selected>

SELECT * INTO backup_tblCategories

FROM tblCategories




SELECT DISTINCT

DISTINCT keyword elimitnates rows that arerepeateing from the result set of a SELECTstatement

Syntax:SELECT DISTINCT <column eliminate>FROM <table name>

Ex: SELECT DISTINCT cat_name FROM

tblCategories




SELECT WHERE

WHERE used to conditionally select or limit records retrieved bythe query

Syntax:SELECT <collection>

FROM <table name>

WHERE <expression>

Where:

collection: list of column name in any table (include

between columns “,” if retrieves than one) or any(function, variable,..)

table name: List of table

Expression: Operators




SELECT WHERE- Expression

The different operators that can be used with theWHERE <Expression>

Operator Description

=,>=,<,>,<= Compare operators

< >, != Not equal to

AND, OR, NOT WHERE price>=10.5 AND price<=20.5 ORprice=21.0

LIKE Search for pattern ‘%[_^string]%’

BETWEEN WHERE price BETWEEN 10.5 AND 20.5

IN,NOT IN, ALL, ANY „Hellochao‟ IN („C‟, „Hello‟, „chao‟)




Options and Attributes




SELECT ORDER BY, GROUP BY

ORDER BY: Sort query result by one or more columnsfollow ASC, DESC

GROUP BY: clause partition the result set into one ormore subset, can be it uses with HAVING

Syntax:

SELECT <collection>FROM <table name>WHERE <expression>

ORDER BY <column ASC|DESC>GROUP BY <column> [HAVING <expression>]




Example ORDER , GROUP BY

SELECT * FROM tblCategories as c

WHERE 1=1 ORDER BY c.cat_name ASC

SELECT ord_id, cus_name

, sum(pro_price*ord_quantity) as „Totals‟

FROM tblOrderDetails

WHERE 1=1GROUP BY cus_id




SELECT - The LIMIT Clause

The LIMIT clause is used most effectively in a SELECT statement

when it is used with an ORDER BY clause. The LIMIT clause takes two arguments, as the following syntax

shows:

LIMIT [<offset>,] <row count> SELECT * FROM tblCategories as c LIMIT 10

SELECT * FROM tblCategories as c LIMIT 3,5

SELECT title, rating, rental_rate

FROM film

ORDER BY title ASC

LIMIT 5;




Join multi table by key

In a normalized database, groups of data are stored inindividual tables, and relationships are established betweenthose tables to link related data

As a result, often when creating SELECT, UPDATE, orDELETE statements, you want to be able to access data in

different tables to carry out an operation affected by thoserelationships

The real power of a relational database emerges from the abilityto combine multiple entities in a single operation




Using WHERE

Syntax:SELECT <collection columns>

FROM <table_1, table_2>

WHERE <table_1.c_key=table_2.c_key>

c_key: is primary key or foreign

key

Table_1, table_2: Related 1-1, 1-N

or M-N




Example using WHERE

SELECT C.ContactName

,C.City

,O.OrderDate

O.RequiredDate

FROM Customers as C, Orders as O

WHERE C.CustomerID=O.CustomerID




Using Join

SQL supports the following JOIN syntaxes forthe table references part of SELECTstatements and multiple-table DELETE and

UPDATE statements: Table references type:

INNER JOIN

LEFT JOIN

RIGHT JOIN




Using Join[1]

SyntaxSELECT <collection columns>

FROM <table_1>

INNER|LEFT|RIGHT JOIN <table_2>

ON <table_1.c_key=table_2.c_key>

c_key: is primary key or foreign key

Table_1, table_2: Related 1-1, 1-N or M-N




Example using Join

SELECT C.ContactName,C.City

,O.OrderDate

O.RequiredDateFROM Customers as C

INNER JOIN Orders as O

ON C.CustomerID=O.CustomerID




Relation JOIN Statement

Documents

SELECT Statement S2