Question

ATM I am trying to learn how to efficiently use database inidices and would appreciate to get some expert input. I do not have any performance issues currently. I would just like to know, how you would handle your indices with this query:

SELECT B.event, 
       COALESCE(B.system, C.surname || ' ' || C.forename) AS name, 
       C.label, 
       B.timestamp
FROM A            
  INNER JOIN B ON A.event=B.event
  INNER JOIN C ON B.state=C.id
  LEFT OUTER JOIN D ON B.hur=D.id             
WHERE A.id IN(12,13,14,15,...) 
  ORDER BY B.event, B.timestamp

A.id, C.id and D.id are already primary keys

UPDATE
normally i would put INDEX(A.event) and INDEX(B.event, B.timestamp). Is this correct?
And what about B.event, B.state and B.hur ?

Answer 1

Rewrite your query as this:

SELECT  B.event, 
        COALESCE(B.system, C.surname || ' ' || C.forename) AS name, 
        C.label, 
        B.timestamp
FROM    B            
INNER JOIN
        C
ON      C.id = B.state
LEFT OUTER JOIN
        D
ON      D.id = B.hur
WHERE   B.event IN
        (
        SELECT  event
        FROM    A
        WHERE   A.id IN (12, 13, 14, 15)
        )
ORDER BY
        B.event, B.timestamp

, and create a composite index on B (event, timestamp)