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SELECT
-- T1.*,
T2.STUID,
T2.APPID,
T2.APPNAME,
T2.BEGINDATE,
T2.ENDDATE
FROM
t_stu T1
LEFT JOIN (
SELECT
StuID,AppID,AppName,BeginDate,EndDate
FROM
t_olzj
UNION ALL
SELECT
StuID,AppID,AppName,BeginDate,EndDate
FROM
t_olgz
UNION ALL
SELECT
StuID,AppID,AppName,BeginDate,EndDate
FROM
t_olxj
) AS T2 ON T1.ID = T2.StuID
LIMIT 0,
100
EXPLAIN
SELECT
-- T1.*,
T2.STUID,
T2.APPID,
T2.APPNAME,
T2.BEGINDATE,
T2.ENDDATE
FROM
t_stu T1 FORCE index (id)
LEFT JOIN
t_olgz
AS T2 ON T1.ID = T2.StuID
;
EXPLAIN
SELECT
-- T1.*,
T2.STUID,
T2.APPID,
T2.APPNAME,
T2.BEGINDATE,
T2.ENDDATE
FROM
fx_student T1 FORCE index (id)
LEFT JOIN
(select * FROM
t_olgz FORCE INDEX(stuID)
)
t2 ON T1.ID = T2.StuID
LIMIT 0,
100;