Question

Well I have a table in sql and it contains date column with dates in it and I need to find invalid dates in a leap year e.g.
invalid dates i.e. 31st Feb. or 29th Feb. in a non leap year.

A simple query will help.

Answer 1

You can use ISDATE function of sql server. Please refer:
ISDATE (Transact-SQL),
Validate DateTime String in SQL Server 2005

Sample:

SELECT dt, ISDATE(dt) ValidDate
FROM(
    SELECT '31-Feb-2012' AS dt UNION
    SELECT '31-Jan-2012' AS dt 
)x

ISDATE returns 1 if the expression is a valid date, time, or datetime value; otherwise, 0.

You can check your existing table data using:

SELECT 
    date_of_birth, 
    ISDATE(date_of_birth) ValidDate 
FROM 
    YourTable