如何在MySQL中对数字字符串使用比较运算符? [英] How to use comparison operator for numeric string in mysql?

问题描述

我有一个employee表，该表具有类似varchar类型的经验，该字段合并了年份和月份总数，并用破折号(-)分隔，因此我必须按具有3年以上经验的年份筛选经验./p>

我的表结构:

所以现在我必须拥有超过3年的ID经验. 我尝试如下，

SELECT * FROM employee WHERE experience LIKE '>=3%';

我知道比较运算符将不支持字符串，但是对此我没有任何新的解决方案，有解决方案吗?

解决方案

基于转换为数字的更好答案:

select * from employee where cast(substring(experience, 1, instr(experience, '-')-1) as signed) >= 3;

mysql> select cast(substring('11-3', 1, instr('11-3', '-')-1) as signed);
+------------------------------------------------------------+
| cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) |
+------------------------------------------------------------+
|                                                         11 |
+------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) > 3;
+----------------------------------------------------------------+
| cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) > 3 |
+----------------------------------------------------------------+
|                                                              1 |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) >= 3;
+-----------------------------------------------------------------+
| cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) >= 3 |
+-----------------------------------------------------------------+
|                                                               1 |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('3-0', 1, instr('3-0', '-')-1) as signed) >= 3;
+---------------------------------------------------------------+
| cast(substring('3-0', 1, instr('3-0', '-')-1) as signed) >= 3 |
+---------------------------------------------------------------+
|                                                             1 |
+---------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('2-11', 1, instr('2-11', '-')-1) as signed) >= 3;
+-----------------------------------------------------------------+
| cast(substring('2-11', 1, instr('2-11', '-')-1) as signed) >= 3 |
+-----------------------------------------------------------------+
|                                                               0 |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('22-11', 1, instr('22-11', '-')-1) as signed) >= 3; 
+-------------------------------------------------------------------+
| cast(substring('22-11', 1, instr('22-11', '-')-1) as signed) >= 3 |
+-------------------------------------------------------------------+
|                                                                 1 |
+-------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('11-0', 1, instr('11-0', '-')-1) as signed) >= 3; 
+-----------------------------------------------------------------+
| cast(substring('11-0', 1, instr('11-0', '-')-1) as signed) >= 3 |
+-----------------------------------------------------------------+
|                                                               1 |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

unsigned对于可读性可能会更好.不会对查询产生任何影响.

I have an employee table which has field like experience with varchar type, this field combines both total year and total month separated by dash(-), so I have to filter experience by year who has more than 3 years experience.

my table structure:

So now I have to get more than 3 years experienced id's. I tried like below,

SELECT * FROM employee WHERE experience LIKE '>=3%';

I know comparison operator will not support for string but I do not have any new solution for that, Is there any solution?

解决方案

better answer based on converting to number:

select * from employee where cast(substring(experience, 1, instr(experience, '-')-1) as signed) >= 3;

mysql> select cast(substring('11-3', 1, instr('11-3', '-')-1) as signed);
+------------------------------------------------------------+
| cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) |
+------------------------------------------------------------+
|                                                         11 |
+------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) > 3;
+----------------------------------------------------------------+
| cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) > 3 |
+----------------------------------------------------------------+
|                                                              1 |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) >= 3;
+-----------------------------------------------------------------+
| cast(substring('11-3', 1, instr('11-3', '-')-1) as signed) >= 3 |
+-----------------------------------------------------------------+
|                                                               1 |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('3-0', 1, instr('3-0', '-')-1) as signed) >= 3;
+---------------------------------------------------------------+
| cast(substring('3-0', 1, instr('3-0', '-')-1) as signed) >= 3 |
+---------------------------------------------------------------+
|                                                             1 |
+---------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('2-11', 1, instr('2-11', '-')-1) as signed) >= 3;
+-----------------------------------------------------------------+
| cast(substring('2-11', 1, instr('2-11', '-')-1) as signed) >= 3 |
+-----------------------------------------------------------------+
|                                                               0 |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('22-11', 1, instr('22-11', '-')-1) as signed) >= 3; 
+-------------------------------------------------------------------+
| cast(substring('22-11', 1, instr('22-11', '-')-1) as signed) >= 3 |
+-------------------------------------------------------------------+
|                                                                 1 |
+-------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast(substring('11-0', 1, instr('11-0', '-')-1) as signed) >= 3; 
+-----------------------------------------------------------------+
| cast(substring('11-0', 1, instr('11-0', '-')-1) as signed) >= 3 |
+-----------------------------------------------------------------+
|                                                               1 |
+-----------------------------------------------------------------+
1 row in set (0.00 sec)

unsigned would probably be better for readability. wouldn't likely have any affect on the query.

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