COUNT

描述

返回指定列的非NULL记录数，或者记录总数

语法

COUNT(DISTINCT <expr> [,<expr>,...])
COUNT(*)
COUNT(<expr>)

参数

参数	说明
<expr>	条件表达式（列名）

返回值

返回值为数值类型。如果expr为NULL，则不参数统计

举例

select * from test_count;

+------+------+------+
| id   | name | sex  |
+------+------+------+
|    1 | 1    |    1 |
|    2 | 2    |    1 |
|    3 | 3    |    1 |
|    4 | 0    |    1 |
|    4 | 4    |    1 |
|    5 | NULL |    1 |
+------+------+------+

select count(*) from test_count;

+----------+
| count(*) |
+----------+
|        6 |
+----------+

select count(name) from test_insert;

+-------------+
| count(name) |
+-------------+
|           5 |
+-------------+

select count(distinct sex) from test_insert;

+---------------------+
| count(DISTINCT sex) |
+---------------------+
|                   1 |
+---------------------+

select count(distinct id,sex) from test_insert;

+-------------------------+
| count(DISTINCT id, sex) |
+-------------------------+
|                       5 |
+-------------------------+