Teradata Update Table from Select Statement

Question

Sorry if the title is unclear. Basically I\'m trying to select certain records from multiple tables then update a certain column value for the returned records.

T-SQ

Answer 1

Have you tried the following syntax with Teradata:

UPDATE CUSTOMERS C1
  FROM (SELECT C2.LINK_ID
          FROM CUSTOMERS C2
         INNER JOIN RESTAURANTS R2
            ON C2.LINK_ID = R2.LINK_ID
        WHERE R2.REST_TYPE = 'DINER'
          AND C2.LIKES_US IS NULL) D1
   SET LIKES_US = 'Y'
 WHERE C1.LINK_ID = C2.LINK_ID

Answer 2

I think that in this specific case, the below query will perform a little better since it needs one less join.

UPDATE C
FROM CUSTOMERS  C, RESTAURANTS R
SET LIKES_US = 'Y'
WHERE 
C.LINK_ID = R.LINK_ID
AND R.REST_TYPE = 'DINER'
AND C.LIKES_US IS NULL