对于from子句中的表，当一列是相互的时简化where子句

Question

I would like to learn if there is any more efficient way to write the query below:

SELECT * 
FROM   requests srp 
       INNER JOIN surgeons rpsur 
               ON rpsur.id = srp.surgeon_id 
       LEFT OUTER JOIN #usersurgeons usersurgeons 
                    ON usersurgeons.surgeon_id = srp.surgeon_id 
       LEFT OUTER JOIN surgeons LOsurgeons 
                    ON usersurgeons.surgeon_id = LOsurgeons.id 
       LEFT OUTER JOIN provsurgeons LOprovsurgeons 
                    ON LOprovsurgeons.id = LOsurgeons.provsurgeon_id 
       INNER JOIN #selectedsurgeons up 
               ON up.surgeon_id = rpsur.id 
       LEFT OUTER JOIN provsurgeons ps 
                    ON ps.id = rpsur.provsurgeon_id 
WHERE  rpsur.isprimary = 0 
       AND usersurgeons.isprimary = 0 
       AND LOsurgeons.isprimary = 0 
       AND LOprovsurgeons.isprimary = 0 
       AND up.isprimary = 0 
       AND ps.isprimary = 0 

I am not happy with the where clause here, is there any more professional way to write this, rather than adding the clauses to the join lines (such as on xx.id = yy.id and xx.isPrimary=0 )??

Answer 1

From this query alone there are not many things that can be said. You should consider adding some more context (how do you get data into those temporary tables and the structure of %surgeons tables):

1) Select * makes almost impossible to use any index and also provides a lot of columns ( Requests.* , surgeons.* , Provsurgeons.* etc.) in your final result. Return only the columns that you need.

2) If isPrimary = 0 filtering is performed often in your queries (not just this one), you can consider creating a view that fetches data filtered by isPrimary = 0. Eg vwSurgeons , vwProvsurgeons . Then, you can just JOIN directly to the view instead of the table.

3) [already mentioned in the comments] Any condition that excludes NULL values for the OUTER JOIN ed table will transform the OUTER into INNER .

Answer 2

Instead of joining all tables and having a where clause at the end, use a derived tables only with filtered records. This way your query performance will be better.

SELECT * FROM requests srp INNER JOIN surgeons rpsur ON rpsur.id = srp.surgeon_id LEFT OUTER JOIN ( SELECT * FROM #usersurgeons WHERE isprimary = 0 )usersurgeons ON usersurgeons.surgeon_id = srp.surgeon_id LEFT OUTER JOIN ( SELECT * FROM surgeons WHERE isprimary = 0 )LOsurgeons ON usersurgeons.surgeon_id = LOsurgeons.id LEFT OUTER JOIN ( SELECT * FROM provsurgeons WHERE isprimary = 0 )LOprovsurgeons ON LOprovsurgeons.id = LOsurgeons.provsurgeon_id INNER JOIN ( SELECT * FROM #selectedsurgeons WHERE isprimary = 0 )up ON up.surgeon_id = rpsur.id LEFT OUTER JOIN ( SELECT * FROM provsurgeons WHERE isprimary = 0 ) ps ON ps.id = rpsur.provsurgeon_id WHERE rpsur.isprimary = 0