标签：指定 col distinct 选择 ble 不同 nbsp 去重 sel
COUNT() 函数返回匹配指定条件的行数。
COUNT(column_name)函数返回指定列的值的数目（NULL不计入）
SELECT COUNT(column_name) FROM table_name;
COUNT(*) 函数返回表中的记录数：
SELECT COUNT(*) FROM table_name;
例：
从SC表中选出S=1的数量
select count(*) from SC where S=1
选择SC表中列S下不同的值的数量
select count(*) from (select distinct s from sc) as aaa
选择SC表中得分89的学生的数量（去重）
select count(S) from (select distinct S from SC where score=89)
标签：指定 col distinct 选择 ble 不同 nbsp 去重 sel
原文地址：https://www.cnblogs.com/jiablogs/p/8806613.html
