MySQL不是很慢

Question

我希望有人能帮助我。这是 SQL 查询:

SELECT * 
FROM pf_profilvisit 
WHERE u1 = '".$user."' 
   AND u2 NOT IN (
      SELECT empf FROM pf_mailbox WHERE abs = '".$user."'
   ) 
   AND u2 NOT IN (
      SELECT abs FROM pf_mailbox WHERE empf = '".$user."'
   ) 
ORDER BY id DESC);

如何让它更快？

Answer 1

SELECT pf_profilvisit.* 
FROM pf_profilvisit
LEFT JOIN  pf_mailbox 
ON pf_profilvisit.u2 = pf_mailbox.empf 
  OR pf_profilvisit.u2 = pf_mailbox.abs
WHERE pf_profilvisit.u1 = '".$user."' 
  AND pf_mailbox.empf IS NULL
  AND pf_mailbox.abs IS NULL
ORDER BY pf_profilvisit.id DESC;

你能展示一下你的表架构吗？您是否为 pf_mailbo.abs、pf_mailbo.empf、pf_profilvisit.u1、pf_profilvisit.u2、pf_profilvisit.id 列编制了索引？