sql自定义变量的基本用法

1.employee表 按 salary进行排名,相同的排名相同,并且排名连续: sql: SELECT @num := IF(@salary = salary, @num, @num + 1) num, //另@num重新赋值(如果@salary = 当前记录的salary,@num赋值为@num,否则赋值为@num+1 ) @salary := salary salary FROM emplo

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