get difference between two double precision columns

[kani98]

I am trying to compute the difference between two double precision columns, start_time and stop_time. I used this select statement: Select (stop_time - start_time) AS Duration From table; The result I get back is a column name Duration with empty cells. What should be the correct syntax? Thanks.

[Blue_Boy]

What are datatypes of columns stop_time and start_time ?

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[kani98]

the columns are of type double.

[Wendelius]

Could it be that either stop_time or start_time is NULL. In that case the result would be NULL.

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