Using Case-When in Teradata

Simple problem but driving me crazy for a while. Have following table in Teradata:

A B 112211 113311 56 226144 61 996688 66 005400 771277 

For the blank fields in col-B need to pull the numbers from col-A like:

SELECT A CASE 'B' WHEN 'B' IS NULL THEN SUBSTR('A',3,4) END AS 'B' FROM TABLE_T1; 

Referred some documentation but not getting what's going wrong in the above query. This query will work on MySQL but why not in Teradata.

Expected O/P:

A B 112211 22 113311 56 226144 61 996688 66 005400 54 771277 12 

1 Answer

You can use this form of case expression note the difference is case when ... not case b when .... Also use single quotes for literals only, use double quotes for identities. (Note sure why you used single quotes.)

SELECT A , CASE WHEN B IS NULL THEN SUBSTR(A,3,4) ELSE B END AS "B" FROM TABLE_T1; 

But you can also use coalesce() for this I believe:

SELECT A , coalesce(B ,SUBSTR(A,3,4) AS "B" FROM TABLE_T1;