Question

I need to redo sql statement in legacy Foxpro application and don’t understand whether it is meaningful at all. Syntax is a bit specific – it extracts data from temporary table into the same temporary table ( overwriting) with some joins.

SELECT aa.*,b.spa_date FROM (ALIAS()) aa INNER JOIN jobs ON aa.seq=jobs.seq ;
LEFT JOIN job2 ON jobs.job_no=job2.rucjob;
left join jobs b on b.job_no=job2.job_no;
WHERE jobs.qty1<>0 INTO CURSOR (ALIAS())

Since only one field is added from joined tables ( spa_date ) is there any point in 2 left joins or I am missing something. Isn’t it equivalent to

SELECT aa.*,jobs.spa_date FROM (ALIAS()) aa INNER JOIN jobs ON aa.seq=jobs.seq ;
WHERE jobs.qty1<>0 INTO CURSOR (ALIAS())

Answer 1

They are different because b.spa_date come from the second left join. You may be missing filtered rows without both left joins.

You would need to know the intent of the original query and perhaps rewrite it to make more sense but I’d say the two queries are different.