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| Тема |
 sql server query optimizations |
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| Автор |
LukavBlaginar (минаващ) |
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| Публикувано | 12.02.07 20:15 |
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Kakvo mislite za slednoto:
When we need to filter by many criteria the data retrieved from the data base, and not all of the criteria are always set for example if we want to retrieve either all subjects from subjects table, or subjects which first name starts with "A" we have two approaches:
1. We are able to build SQL statement in the client application, and execute the statement, in the first case the SQL statement would be:
Select * from Subjects
In the second case the SQL statement would be:
Select * from Subjects where FirstName like ('A%')
In general it is not good to prepare SQL statement in the client application and execute it, because of possibility of SQL injection and also increasing the network traffic
2. We are able to use stored procedure following the template:
Create Procedure GetSubjectsProc
(
@CharFirstName as char(30) = Null
)
As
Begin
Select
*
From
Subjects
Where
(@CharFirstName is Null or FirstName like (@CharFirstName))
End
If we want to select all subject we will call the stores procedure with null parameter, and at line (@CharFirstName is Null or FirstName like (@CharFirstName)) only the first part of the condition will be calculated.
If we want to select all subjects, which first name starts with 'A*', we will execute the stored procedure with parameter 'A*', and at line (@CharFirstName is Null or FirstName like (@CharFirstName)) because the
first part of the condition is false the second part of the condition will be executed and the result will be all subjects which first name starts with 'A*'
Ako imate ideia za uskoriavane na performance na SQL Server chrez queries, spodeliate.
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