目錄
1，COUNT 計算總量
select count(*) from <表名>;
select count(1) from <表名>; 【* 和數字的意義完全相同】
select count(<列名>) from <表名>; 【只會統計有效值，null是不會進行統計的】
MariaDB [mydb]> select * from score;
+-------+-----------+------+----------+--------+
| id | name | math | language | sports |
+-------+-----------+------+----------+--------+
| 20001 | 小明 | 81 | 86 | 93 |
| 20002 | 小紅 | 86 | 86 | 89 |
| 20003 | 小張 | 77 | 83 | 93 |
| 20004 | 露絲 | 88 | 78 | 65 |
| 20005 | 麗麗 | 92 | 94 | 64 |
| 20006 | 李明 | 75 | 78 | 88 |
| 20007 | 張大明 | 54 | 65 | 95 |
+-------+-----------+------+----------+--------+
7 rows in set (0.000 sec)
MariaDB [mydb]> select count(*) from score;
+----------+
| count(*) |
+----------+
| 7 |
+----------+
1 row in set (0.001 sec)
MariaDB [mydb]> select count(1) from score;
+----------+
| count(1) |
+----------+
| 7 |
+----------+
1 row in set (0.001 sec)
MariaDB [mydb]> select count(name) from score;
+-------------+
| count(name) |
+-------------+
| 7 |
+-------------+
1 row in set (0.001 sec)
2，MAX 求最大值
select max(<列名>) from <表名>;
MariaDB [mydb]> select * from score;
+-------+-----------+------+----------+--------+
| id | name | math | language | sports |
+-------+-----------+------+----------+--------+
| 20001 | 小明 | 81 | 86 | 93 |
| 20002 | 小紅 | 86 | 86 | 89 |
| 20003 | 小張 | 77 | 83 | 93 |
| 20004 | 露絲 | 88 | 78 | 65 |
| 20005 | 麗麗 | 92 | 94 | 64 |
| 20006 | 李明 | 75 | 78 | 88 |
| 20007 | 張大明 | 54 | 65 | 95 |
+-------+-----------+------+----------+--------+
7 rows in set (0.000 sec)
MariaDB [mydb]> select max(math) from score;
+-----------+
| max(math) |
+-----------+
| 92 |
+-----------+
1 row in set (0.001 sec
3，MIN 求最小值
select min(<列名>) from <表名>;
MariaDB [mydb]> select name,min(math) 最低分 from score;
+--------+-----------+
| name | 最低分 |
+--------+-----------+
| 小明 | 54 |
+--------+-----------+
1 row in set (0.001 sec)
4，SUM求和
select sum(<列名>) from <表名>;
MariaDB [mydb]> select sum(math) from score;
+-----------+
| sum(math) |
+-----------+
| 553 |
+-----------+
1 row in set (0.001 sec)
MariaDB [mydb]>
MariaDB [mydb]> select name, math+language+sports 總分 from score;
+-----------+--------+
| name | 總分 |
+-----------+--------+
| 小明 | 260 |
| 小紅 | 261 |
| 小張 | 253 |
| 露絲 | 231 |
| 麗麗 | 250 |
| 李明 | 241 |
| 張大明 | 214 |
+-----------+--------+
7 rows in set (0.001 sec)
5，AVG 求平均值
select avg(<列名>) from <表名>;
MariaDB [mydb]> select avg(math) 數學平均分, avg(language) 語文平均分, avg(sports) 體育平均分 from score;
+-----------------+-----------------+-----------------+
| 數學平均分 | 語文平均分 | 體育平均分 |
+-----------------+-----------------+-----------------+
| 79.0000 | 81.4286 | 83.8571 |
+-----------------+-----------------+-----------------+
1 row in set (0.001 sec)