Redshift Error when executing the delete script with EXISTS function. The Select runs fine for this query - amazon-web-services

Question

This Redshift query fails -
DELETE FROM TBL_1 stg
WHERE EXISTS (
WITH CCDA as (
SELECT
row_number() OVER (PARTITION BY emp_id,customer_id ORDER BY seq_num desc) rn
, *
FROM TBL_2
WHERE end_dt > (SELECT max(end_dt) FROM TBL_3)
)
SELECT emp_id,customer_id FROM CCDA WHERE rn = 1
AND stg.emp_id = CCDA.emp_id
AND stg.customer_id = CCDA.customer_id
);
Error: Invalid operation: syntax error at or near "stg"
However, the below query runs fine -
SELECT * FROM TBL_1 stg
WHERE EXISTS (
WITH CCDA as (
SELECT
row_number() OVER (PARTITION BY emp_id,customer_id ORDER BY seq_num desc) rn
, *
FROM TBL_2
WHERE end_dt > (SELECT max(end_dt) FROM TBL_3)
)
SELECT emp_id,customer_id FROM CCDA WHERE rn = 1
AND stg.emp_id = CCDA.emp_id
AND stg.customer_id = CCDA.customer_id
);
Am I missing something?

Answer 1

You cannot use an alias in a DELETE statement for the target table. "stg" cannot be used as the alias and this is why you are getting this error.
Also to reference other tables in a DELETE statement you need to use the USING clause.
See: https://docs.aws.amazon.com/redshift/latest/dg/r_DELETE.html
A quick stab of what this would look like (untested):
WITH CCDA as (
SELECT
row_number() OVER (PARTITION BY emp_id,customer_id ORDER BY seq_num desc) rn
, *
FROM TBL_2
WHERE end_dt > (SELECT max(end_dt) FROM TBL_3)
)
DELETE FROM TBL_1
USING CCDA
WHERE CCDA.rn = 1
AND TBL_1.emp_id = CCDA.emp_id
AND TBL_1.customer_id = CCDA.customer_id
;