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Obě strany předchozí revize Předchozí verze Následující verze | Předchozí verze | ||
programovani:sql [01.10.2011 14:41] miloush [Metadata] |
programovani:sql [20.11.2011 15:36] (aktuální) miloush |
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Řádek 11: | Řádek 11: | ||
=== Hierarchie cizích klíčů === | === Hierarchie cizích klíčů === | ||
<code> | <code> | ||
- | DECLARE @tableName sysname = N'OrderOut'; | + | DECLARE @tableName sysname = NULL; |
DECLARE @printDepth int = 5; | DECLARE @printDepth int = 5; | ||
Řádek 47: | Řádek 47: | ||
SELECT Parent, ParentColumn, Child, ChildColumn, Pass, DeleteAction, UpdateAction, ConstraintName | SELECT Parent, ParentColumn, Child, ChildColumn, Pass, DeleteAction, UpdateAction, ConstraintName | ||
FROM @Dependencies WHERE Parent = @tableName OR @tableName IS NULL | FROM @Dependencies WHERE Parent = @tableName OR @tableName IS NULL | ||
+ | ORDER BY Parent, Child, ParentColumn, ChildColumn | ||
| | ||
SELECT @c1 = MIN(Child) FROM @Dependencies WHERE Parent = @tableName | SELECT @c1 = MIN(Child) FROM @Dependencies WHERE Parent = @tableName | ||
Řádek 81: | Řádek 82: | ||
SELECT @c1 = MIN(Child) from @Dependencies where Parent = @tableName AND Child > @c1; | SELECT @c1 = MIN(Child) from @Dependencies where Parent = @tableName AND Child > @c1; | ||
END; | END; | ||
- | |||
</code> | </code> | ||
+ | ==== Procedury ==== | ||
+ | === SET vs. SELECT === | ||
+ | - SET is the ANSI standard for variable assignment, SELECT is not. | ||
+ | - SET can only assign one variable at a time, SELECT can make multiple assignments at once. | ||
+ | - **SCALAR** If assigning from a query, SET can only assign a scalar value. If the query returns multiple values/rows then SET will raise an error. SELECT will assign one of the values to the variable and hide the fact that multiple values were returned (so you'd likely never know why something was going wrong elsewhere - have fun troubleshooting that one) | ||
+ | - **NULL** When assigning from a query if there is no value returned then SET will assign NULL, where SELECT will not make the assignment at all (so the variable will not be changed from it's previous value) | ||
+ | - As far as speed differences - there are no direct differences between SET and SELECT. However SELECT's ability to make multiple assignments in one shot does give it a slight speed advantage over SET. | ||
+ | |||
+ | http://vyaskn.tripod.com/differences_between_set_and_select.htm | ||
programovani/sql.1317472863.txt.gz · Poslední úprava: 01.10.2011 14:41 autor: miloush