Declare a variable in RedShift – Amazon-web-services

The Solutions:

Solution 1: Variable Declaration in Redshift

Amazon Redshift does not support variable declaration in the same way as SQL Server. The `DECLARE` keyword is used solely for cursors, and `SET` is not a valid syntax for variable assignment.

As of 2016, Redshift also does not have Scalar User Defined Functions (UDFs) that can act as stored variables.

Therefore, it is not currently possible to declare variables in Redshift.

Solution 2: Using WITH construct

As a variation on the theme, you can also use a WITH construct:

<!– language: lang-sql –>

WITH tmp_variables AS (
SELECT 
   '2015-01-01'::DATE AS StartDate, 
   'some string'      AS some_value,
   5556::BIGINT       AS some_id
)

SELECT *
FROM Orders
WHERE OrderDate >= (SELECT StartDate FROM tmp_variables);

Solution 4: Using psql variables

Note that if you are using the psql client to query, psql variables can still be used as always with Redshift:

$ psql --host=my_cluster_name.clusterid.us-east-1.redshift.amazonaws.com \
     --dbname=your_db   --port=5432 --username=your_login -v dt_format=DD-MM-YYYY

# select current_date;     
    date    
------------
 2015-06-15
(1 row)

# select to_char(current_date,:'dt_format');
  to_char   
------------
 15-06-2015
(1 row)

# \set
AUTOCOMMIT = 'on'
...
dt_format = 'DD-MM-YYYY'
...
# \set dt_format 'MM/DD/YYYY'
# select to_char(current_date,:'dt_format');
  to_char   
------------
 06/15/2015
(1 row)

Solution 5: Using User Defined Functions (UDFs)

In RedShift, you can utilize User Defined Functions (UDFs) to declare a variable and use it in queries. Here’s how you can do it:

1. Create a UDF to define the variable:

   CREATE FUNCTION my_const()
       RETURNS CSTRING IMMUTABLE AS 
       $$ return 'my_string_constant' $$ language plpythonu;
   

2. In your query, call the UDF to retrieve the variable:

   SELECT *
   FROM Orders
   WHERE OrderDate >= my_const();
   

Please note that to use this approach, you may require specific access permissions on your RedShift database. For more information, refer to the documentation on UDF security and privileges.