EXPLAIN
select a.id
FROM oa_attachment a
LEFT JOIN sys_user u ON u.id = a.create_by
LEFT JOIN sys_user v ON v.id = a.writer
where a.del_flag=0
优化统一u.id , a.create_by,v.id ,a.writer的编码
EXPLAIN
优化统一u.id , a.create_by,v.id ,a.writer的编码
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