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 |
+-------------------------+