MySQL学习日记(19)比较运算符

比较运算符

比较对象 比较运算符 子查询

mysql> SELECT * FROM 运算符例子;
+----+------+
| id | 数值 |
+----+------+
|  1 |    1 |
|  2 |    3 |
|  3 |    5 |
|  4 |    7 |
|  5 |    9 |
|  6 |   11 |
|  7 |   13 |
+----+------+
7 rows in set (0.01 sec)

mysql> SELECT * FROM 运算符例子2;
+----+------+
| id | 数值 |
+----+------+
|  1 |    2 |
|  2 |    4 |
|  3 |    6 |
|  4 |    8 |
|  5 |   10 |
|  6 |   12 |
|  7 |   14 |
+----+------+
7 rows in set (0.00 sec)

#查找 运算符例子表中 数值小于 运算符例子2表中 id=5(10)的数据
mysql> SELECT id,数值 FROM 运算符例子 WHERE 数值 < (SELECT 数值 FROM 运算符例子2 WHERE id=5);
+----+------+
| id | 数值 |
+----+------+
|  1 |    1 |
|  2 |    3 |
|  3 |    5 |
|  4 |    7 |
|  5 |    9 |
+----+------+
5 rows in set (0.00 sec)
#10>9=1(true)
mysql> SELECT (SELECT 数值 FROM 运算符例子2 WHERE id=5) > (SELECT 数值 FROM 运算符例子 WHERE id = 1) AS 比较;
+------+
| 比较 |
+------+
|    1 |
+------+
1 row in set (0.00 sec)
#10<9=0(false)
mysql> SELECT (SELECT 数值 FROM 运算符例子2 WHERE id=5) < (SELECT 数值 FROM 运算符例子 WHERE id = 1) AS 比较;
+------+
| 比较 |
+------+
|    0 |
+------+
1 row in set (0.00 sec)

用ANY、SOME或ALL修饰的比较运算符

运算符/关键字	ANY	SOME	ALL
>、>=	最小值	最小值	最大值
<、<=	最大值	最大值	最小值
=	任意值	任意值
<>、!=、			任意值

比较对象 比较运算符 ANY(子查询)

• 假设子查询返回结果为值1,值2,值3举例:
  值 > ANY(...)
  实际上等于 值 > 值1 OR 值>值2 OR 值>值3
  相当于 或

  
  
  ANY

比较对象 比较运算符 SOME(子查询)

• 和ANY一样也相当于 或

SOME

比较对象 比较运算符 ALL(子查询)

• 假设子查询返回结果为值1,值2,值3举例:
  值 > SOME(...)
  实际上等于 值 > 值1 AND 值>值2 AND 值>值3
  相当于 与

  
  
  ALL

[NOT] IN

这个就相当于Python中的find,用来确认是两组数据是否相同或不同

值 运算符 [NOT] IN (子查询)

• =ANY运算符与IN等效
• != ALL或者<>ALL运算与NOT IN等效

mysql> select * from 运算符例子;
+----+------+
| id | 数值 |
+----+------+
|  1 |    1 |
|  2 |    3 |
|  3 |    5 |
|  4 |    7 |
|  5 |    9 |
|  6 |   11 |
|  7 |   13 |
+----+------+
7 rows in set (0.00 sec)

mysql> select * from 运算符例子2;
+----+------+
| id | 数值 |
+----+------+
|  1 |    2 |
|  2 |    4 |
|  3 |    6 |
|  4 |    8 |
|  5 |   10 |
|  6 |   12 |
|  7 |   14 |
|  8 |   13 |
+----+------+
8 rows in set (0.00 sec)

mysql> select id,数值 from 运算符例子 WHERE 数值 != ALL(select 数值 from 运算符例子2 WHERE 数值);
+----+------+
| id | 数值 |
+----+------+
|  1 |    1 |
|  2 |    3 |
|  3 |    5 |
|  4 |    7 |
|  5 |    9 |
|  6 |   11 |
+----+------+
6 rows in set (0.00 sec)

mysql> select id,数值 from 运算符例子 WHERE 数值 NOT IN(select 数值 from 运算符例子2 WHERE 数值);
+----+------+
| id | 数值 |
+----+------+
|  1 |    1 |
|  2 |    3 |
|  3 |    5 |
|  4 |    7 |
|  5 |    9 |
|  6 |   11 |
+----+------+
6 rows in set (0.00 sec)

mysql> select id,数值 from 运算符例子 WHERE 数值 = ANY(select 数值 from 运算符例子2 WHERE 数值);
+----+------+
| id | 数值 |
+----+------+
|  7 |   13 |
+----+------+
1 row in set (0.00 sec)

mysql> select id,数值 from 运算符例子 WHERE 数值 IN (select 数值 from 运算符例子2 WHERE 数值);
+----+------+
| id | 数值 |
+----+------+
|  7 |   13 |
+----+------+
1 row in set (0.00 sec)