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ON MySQL 5.7, generated columns are not allowed with non-deterministic function.

The query that I need to optimize is executing on a bulky table.

Where clause is causing a full scan on the table, need to optimize that.

The column is DateTime type, we have to use the unix_timestamp function as per application

WHERE UNIX_TIMESTAMP(Last_Used_Time) > 1540874005

I am trying to convert UNIX_TIMESTAMP(Last_Used_Time) into a generated column but throws an error disallowed function used in the expression.

Any workaround to allow MySQL to use generated/virtual column with unix_timestamp function.

  • You are barking up a specific tree. Let's back up and see if there is another way to solve the problem. Please provide SHOW CREATE TABLE and the query that is so slow. – Rick James Oct 31 '18 at 5:24
  • The column is DateTime type If so why you use timezone-dependent function? If you know datetime you want to compare with - why you do not compare with datetime literal immediately? – Akina Oct 31 '18 at 5:24
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Don't convert the column's value, convert your criterium:

WHERE Last_Used_Time > from_unixtime(1540874005)
  • That's brilliant, thanks for the suggestion. – Vinith Nair Oct 31 '18 at 5:31
  • Hi Gerard, I tried as per your suggestion, query execution time reduces from 4 min to 4 seconds, so query seem optimized, but on comparing records, I am finding the records obtained from before and after query vary slightly. Few records are not matching, not sure why so, any reason that you are aware of? – Vinith Nair Oct 31 '18 at 10:20
  • Please show last_used_time from a number of matching and no longer matching records (in your question please). – Gerard H. Pille Oct 31 '18 at 14:47
  • Hey Gerard, figured out the issue was, misunderstanding of data from our end. Anyways Thanks for your support. – Vinith Nair Nov 1 '18 at 5:24
  • It's been a pleasure. – Gerard H. Pille Nov 1 '18 at 5:54

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