Does SQLite optimize a query with multiple AND conditions in the WHERE clause?

Question

In SQL databases (I use Python+Sqlite), how to make sure that, if we have 1 million rows, the query

SELECT * FROM mytable WHERE myfunction(description) <          


        

Answer 1

One way that you can force the order of execution is using a case expression. In general, SQL optimizers can re-arrange operations, the one exception is case.

SELECT *
FROM mytable
WHERE (CASE WHEN column2 >= 1000  OR column2 IS NULL THEN 0
            WHEN myfunction(description) < 500 THEN 1
       END) = 1;

Generally, case expressions are discouraged in WHERE clauses . . . one major reason is that they impede optimization. In this case, that is a good thing.