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umberi
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ameselectstock
amefromstock_i
formatio
wherestockid4子查询httpwwwac
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etoYIpsxSPAIC除非能确保内层select只返回一个行的值，否则应在外层where子句中用一个i
限定符selectdisti
ctcolum
_
ameformtable_
amedisti
ct指定检索独有的列值，不重复selectstock
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