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Debian で MySQL 5.1.66-0+squeeze1-log を使用すると、理解できない GROUP BY の結果が得られます。

GROUP BY の場合data、等しくないdata値が結合されますが、これは意味がありません。同じ列 SHA1( ) のハッシュ値を GROUP BY するとdata、すべてが正常に機能し、等しい値のみdataがグループに結合されます。

ここで何が起こっているのですか？GROUP BY は、列の最初の x 文字のみを考慮しているようです。そうでない場合、他になぜこれが起こるのでしょうか? 多分それは私の脳のねじれですか？

data編集 1: (json でエンコードされたレガシー - 私がもっとばかだったときの値の例;) ):

{"a":[{"val":{"tcn":{"1980":"1","1981":"1","1982":"1","1983":"1","1984":"1","1985":"1","1986":"1","1987":"1","1988":"1","1989":"1","1990":"1","1991":"1","1992":"1","1993":"1","1994":"1","1995":"1","1996":"1","1997":"1","1998":"1","1999":"1","2000":"1","2001":"1","2002":"1","2003":"1","2004":"1","2005":"1","2006":"1","2007":"1","2008":"1","2009":"1","2010":"1"},"sic":{"1980":"1","1981":"1","1982":"1","1983":"1","1984":"1","1985":"1","1986":"1","1987":"1","1988":"1","1989":"1","1990":"1","1991":"1","1992":"1","1993":"1","1994":"1","1995":"1","1996":"1","1997":"1","1998":"1","1999":"1","2000":"1","2001":"1","2002":"1","2003":"1","2004":"1","2005":"1","2006":"1","2007":"1","2008":"1","2009":"1","2010":"1"}}}],"b":[{"val":{"tcn":{"1980":"1","1981":"1","1982":"1","1983":"1","1984":"1","1985":"1","1986":"1","1987":"1","1988":"1","1989":"1","1990":"1","1991":"1","1992":"1","1993":"1","1994":"1","1995":"1","1996":"1","1997":"1","1998":"1","1999":"1","2000":"1","2001":"1","2002":"1","2003":"1","2004":"1","2005":"1","2006":"1","2007":"1","2008":"1","2009":"1","2010":"1"},"sic":{"1980":"1","1981":"1","1982":"1","1983":"1","1984":"1","1985":"1","1986":"1","1987":"1","1988":"1","1989":"1","1990":"1","1991":"1","1992":"1","1993":"1","1994":"1","1995":"1","1996":"1","1997":"1","1998":"1","1999":"1","2000":"1","2001":"1","2002":"1","2003":"1","2004":"1","2005":"1","2006":"1","2007":"1","2008":"1","2009":"1","2010":"1"}}}],"0":[{"val":{"com":{"able":"2"}},"str":{"com":{"comm":"According","src":{"1":{"name":"law 256","articles":"B2\/2.11","links":"","type":""},"2":{"name":"law 298","articles":"B.19\/2.3","links":"","type":""}}}}}]}

EDIT 2:コードを省略して申し訳ありません。コードを短く簡単にすると思いました。明らかに逆ですよね…

SELECT
    GROUP_CONCAT(resid) AS ids
    ,data
FROM resdata
GROUP BY data

対。

SELECT
    GROUP_CONCAT(resid) AS ids
    ,CAST(SHA1(data) AS CHAR(40)) AS hash
    ,data
FROM resdata
GROUP BY hash
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