Ed Wagner (1/31/2016)

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Jonathan AC Roberts (1/31/2016)

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CAST(LEFT(OMD, 8) as datetime) + 30 < GETDATE();

This is not good practice, I'm not sure it will even work in versions of SQL Server later than 2005.

You should be using the DATEADD function, i.e.:

DATEADD(dd,30,CONVERT(datetime,LEFT(OMD, 8)) < GETDATE();

The storage of a date is never a good practice. A good idea would be to storage dates in a date/datetime column.

The conversion of a string to a datetime can cause errors if the string contains invalid date values. Even if it doesn't, it'll still be much slower than it would be using a date data type. Doing a calculation on a column will also be slower than it needs to be because the engine has to perform the calculation on every row in the table and then perform the comparison.

A good way of doing the comparison would be to compare a date column against a date that's 30 days ago.

Example: WHERE some_date < DATEADD(day, -30, GETDATE())

Integer addition and subtraction against a datetime data type does work after SQL 2005.