Question

I have two table say T1 and T2 and one column C is common to both. I need an SQL query in which if C is null in T1 it will select from other table.

I tried writing SELECT statement in THEN clause but not running. Don’t know is there any IF ELSE clause in SQL.

Select C, case when c = null Then Select c from T2
from T1

Answer 1

Even better, most RDBMSs support COALESCE, which lets you check multiple values and return the first non-null value.

SELECT COALESCE(T1.C, T2.C) AS C
FROM T1
LEFT OUTER JOIN T2 ON T1.[Primary Key] = T2.[Primary Key]