Re: JOINS AND INDEX NOT USED

[Rick James]

Perhaps OR is the villain... See if this runs faster:

(
SELECT  server.mailhome
    FROM  emailaddress
    INNER JOIN  account
    LEFT JOIN  server ON account.server_current = server.id
    WHERE  emailaddress.domain = 'domain.com'
      AND  emailaddress.lhs = ''
    ORDER BY  emailaddress.lhs DESC
    LIMIT  1
)
UNION
(
SELECT  server.mailhome
    FROM  emailaddress
    INNER JOIN  account
    LEFT JOIN  server ON account.server_current = server.id
    WHERE  emailaddress.domain = 'domain.com'
      AND  emailaddress.lhs = 'emailuser'
    ORDER BY  emailaddress.lhs DESC
    LIMIT  1
)
    ORDER BY  emailaddress.lhs DESC
    LIMIT  1

What is the value of server_current when it ignores the index? Perhaps the cardinality is so poor that it decided that a table scan was faster than bothering to use the index.