count

示例表mingyan

mingyan

SQL COUNT(column_name) 语法

COUNT(column_name) 函数返回指定列的值的数目（NULL 不计入）：

示例：SELECT count(tag) FROM mingyan WHERE tag = 'xiaoli'

SQL COUNT(*) 语法

COUNT(*) 函数返回表中的记录数：

示例：SELECT count(*) FROM mingyan  结果：9

SQL COUNT(DISTINCT column_name) 语法

COUNT(DISTINCT column_name) 函数返回指定列的不同值的数目：

示例：SELECT count(DISTINCT tag) FROM mingyan

查询重复的记录并分组

select remark,count(*),GROUP_CONCAT(id) from t_banner group by remark HAVING count(*)>1