Question

WITH DATA
     AS ( select ACCT_ID_1,  ACCT_ID, ACCT_ID_2 ... from two tables joined by criteria ),
DATA1
     AS (SELECT D1.*
           FROM DATA D1
          WHERE ACCT_ID_1 = ACCT_ID AND ACCT_ID_1 = '101'),
DATA2
     AS (SELECT D2.*
           FROM DATA D2
          WHERE ACCT_ID_2 = ACCT_ID AND ACCT_ID_2 = '101')

I need to get data1 if there is data in data1 ( no data from data2 ) else I need to get from data2. Is it possible using SQL?

Answer 1

This is probably how I’d do it:

WITH data1 AS (
  SELECT 1
  FROM dual
  WHERE 1=2 -- Set to 1 to reverse result
)
, data2 AS (
  SELECT 2
  FROM dual  
)
SELECT *
FROM data1
UNION ALL
SELECT *
FROM data2
WHERE NOT EXISTS (
  SELECT 1
  FROM data1
)

Posted on SQLFiddle as an example.