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Assign variables for dedicated SQL pools in Azure Synapse Analytics

  • Artikkeli

In this article, you'll find essential tips for assigning T-SQL variables in dedicated SQL pool.

Set variables with DECLARE

Variables in dedicated SQL pool are set using the DECLARE statement or the SET statement. Initializing variables with DECLARE is one of the most flexible ways to set a variable value in SQL pool.

DECLARE @v  int = 0
;

You can also use DECLARE to set more than one variable at a time. You can't use SELECT or UPDATE to do the following:

DECLARE @v  INT = (SELECT TOP 1 c_customer_sk FROM Customer where c_last_name = 'Smith')
,       @v1 INT = (SELECT TOP 1 c_customer_sk FROM Customer where c_last_name = 'Jones')
;

You can't initialize and use a variable in the same DECLARE statement. To illustrate the point, the following example is not allowed since @p1 is both initialized and used in the same DECLARE statement. As such, the following example gives an error:

DECLARE @p1 int = 0
,       @p2 int = (SELECT COUNT (*) FROM sys.types where is_user_defined = @p1 )
;

Set values with SET

SET is a common method for setting a single variable.

The following statements are all valid ways to set a variable with SET:

SET     @v = (Select max(database_id) from sys.databases);
SET     @v = 1;
SET     @v = @v+1;
SET     @v +=1;

You can only set one variable at a time with SET. However, compound operators are permissible.

Limitations

You can't use UPDATE for variable assignment.

Next steps

For more development tips, see development overview.