Mysql比较函数

•  COALESCE(value,...)

  返回列表中第一个非空值, 如果没有非空值，返回NULL.

  mysql> SELECT COALESCE(NULL,1);
          -> 1
  mysql> SELECT COALESCE(NULL,NULL,NULL);
          -> NULL

• GREATEST(value1,value2,...)

  返回最大值

  mysql> SELECT GREATEST(2,0);
          -> 2
  mysql> SELECT GREATEST(34.0,3.0,5.0,767.0);
          -> 767.0
  mysql> SELECT GREATEST('B','A','C');
          -> 'C'

 LEAST(value1,value2,...)

返回最小值

mysql> SELECT LEAST(2,0);
        -> 0
mysql> SELECT LEAST(34.0,3.0,5.0,767.0);
        -> 3.0
mysql> SELECT LEAST('B','A','C');
        -> 'A'