您没有做错任何事。这就是JOIN的行为
它是左边的行数X右边的行数,在您的情况下为3 x 2 = 6。
6 x 200 = 1200
试试这个
SQLFiddleSelect rolls.height,rolls.type, SUM(rolls.weight) as W, rollsout.Ww FROM rolls LEFT JOIN (Select height,type, SUM(weight) as Ww From rollsout GROUP BY height, type ) as rollsoutON rolls.height = rollsout.height AND rolls.type= rollsout.type GROUP BY rolls.height,rolls.type
我知道这不适用于SQL Server,但适用于MySQL
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