Re: Index Not being used.

[Rick James]

You have aggregates (SUM) and no GROUP BY? So, you should get one line of output. Yet, you are saying it returns millions of rows.

If it does return millions of rows, what will you do with them? That is a lot to process. Can you 'process' them in sql, and return some smaller resultset.

If ORD_DATE is in the `lines` table, why have `LEFT`? The WHERE clause will exclude them anyway. Once you remove `LEFT`, the optimizer is free to start with `lines`. But then you need these two indexes:

pos_ord_headers: INDEX(ORD_ID) -- perhaps you already have it as a PRIMARY KEY.
pos_ord_lines: INDEX(ORD_DATE)