In MySQL, the SELECT DISTINCT statement is used to return only distinct values means if in a table, a column has duplicate values then SELECT DISTINCT statement will be used to get different values.

I'm (always) using Propel1 and got some errors w. MySQL 5.7 seems Doctrine2 had the same problem > doctrine/orm#5622 The problem seems raised when I tried to make an "order by" with a column being in ...

MySQL で select distinct の対象として多すぎるカラムを指定するとカラム数に比例して遅くなる。 そういった場合、一旦 pk を含む少数のカラムで distinct してから pk で引き直す方が早い。