時間:2024-03-08 08:50作者:下載吧人氣:17
當數(shù)據(jù)量比較大的時候,提升查詢效率就是需要去考慮的事情了。一個百萬級別的表格,如果不做任何優(yōu)化的話,即使是最簡單的查詢語句執(zhí)行起來也是慢的讓人難以接受;當然“優(yōu)化”本身是一個比較復(fù)雜的工程,從設(shè)計表、字段到查詢語句的寫法都有很多講究,這里只考慮索引的方式,且是最普通的索引;
下面的操作中對應(yīng)數(shù)據(jù)庫表w008_execrise_info(8000數(shù)據(jù)量), w008_wf02_info(4000數(shù)據(jù)量)
SELECT
w.*
FROM
w008_wf02_info w
WHERE
w.is_removed =0
AND w.wfno = ‘WF02′
AND EXISTS (
SELECT
1
FROM
w008_execrise_info info
JOIN w008_privilege_allocation P ON (
info.subjecttyp = P.subjecttyp
AND info.gradetyp = P.gradetyp
AND P.loginname = w.create_by
AND P.verifyusers =’yixi_li’
AND P.wftype = 20
)
WHERE
info.is_removed =0
AND info.wfid = w.wfid
)
ORDER BY
create_date DESC
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