شرح استخدام WHERE مع كل جمل SQL

من طرف **SiteAdmin** الخميس يوليو 08, 2010 1:25 pm

The WHERE clause is used to filter records.
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The WHERE Clause
The WHERE clause is used to extract only those records that fulfill a specified criterion.

SQL WHERE Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name operator value

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WHERE Clause Example
The "Persons" table:

City	Address	FirstName	LastName
Sandnes	Timoteivn 10	Ola	Hansen
Sandnes	Borgvn 23	Tove	Svendson
Stavanger	Storgt 20	Kari	Pettersen

Now we want to select only the persons living in the city "Sandnes" from the table above.

We use the following SELECT statement:

الكود:: SELECT * FROM Persons WHERE City='Sandnes'

The result-set will look like this:

City	Address	FirstName	LastName
Sandnes	Timoteivn 10	Ola	Hansen
Sandnes	Borgvn 23	Tove	Svendson

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Quotes Around Text Fields
Quotes = علامات الاقتباس
SQL uses single quotes around text values (most database systems will also accept double quotes).

Although, numeric values should not be enclosed in quotes.

For text values:

This is correct:

الكود:: SELECT * FROM Persons WHERE FirstName='Tove'

This is wrong:

الكود:: SELECT * FROM Persons WHERE FirstName=Tove

For numeric values:

This is correct:

الكود:: [/font][/color] [color=blue][font='Verdana']SELECT * FROM Persons WHERE Year=1965

This is wrong:

الكود:: SELECT * FROM Persons WHERE Year='1965'

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Operators Allowed in the WHERE Clause
With the WHERE clause, the following operators can be used:

Operator....................... Description
Operator ...................... الوصف
=......................................... يساوى
<> ...................................... لا يساوى
>= ...................................... اكبر من او يساوى
<=....................................... اقل من او يساوى
BETWEEN...................... بين قيمتين
LIKE ............................ مثل
IN .............................. قيمة من قيم محددة

Note: In some versions of SQL the <> operator may be written as != ( like in C language