SQL JOIN with two or more tables as output - most efficient way?
- by littlegreen
I have an SQL query that executes a LEFT JOIN on another table, then outputs all results that could be coupled into a designated table. I then have a second SQL query that executes the LEFT JOIN again, then outputs the results that could not be coupled to a designated table. In code, this is something like:
INSERT INTO coupledrecords
SELECT b.col1, b.col2... s.col1, s.col2... FROM bigtable AS b
LEFT JOIN smallertable AS s
ON criterium
WHERE s.col1 IS NOT NULL
INSERT INTO notcoupledrecords
SELECT b.col1, b.col2... bigtable AS b
LEFT JOIN smallertable AS s
ON criterium
WHERE s.col1 IS NULL
My question: I now have to execute the JOIN two times, in order to achieve what I want. I have a feeling that this is twice as slow as it could be. Is this true, and if yes, is there a way to do it more efficiently?
