Assigning variables in Azure SQL Data Warehouse

Tips for assigning T-SQL variables in Azure SQL Data Warehouse for developing solutions.

Setting variables with DECLARE

Variables in SQL Data Warehouse 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 Data Warehouse.

DECLARE @v  int = 0
;

You can also use DECLARE to set more than one variable at a time. You cannot 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 cannot 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. The following example gives an error.

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

Setting 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 cannot use SELECT or UPDATE for variable assignment.

Next steps

For more development tips, see development overview.