如何使用SQL查询在表中的两个字段之间进行减法 [英] How to do subtraction between two fields in a Table using an SQL query

问题描述

我想使用SQL查询显示两个不同的值从两个不同的列减去到第三列.

I want to display the subtraction of two values from two different columns to a third column using a SQL query.

这是表结构:

------------------------------------
id | subject | Time1 | Time2| Time3
------------------------------------
1  | String1 | 50    |  78  | 
2  | String2 | 60    |  99  |  
3  |         |       |      |

如果Time1和Time2都具有数据并存储在Time3中，我想从Time1中减去Time2.

I want to subtract Time2 from Time1 if both Time1 and Time2 has data and store in Time3.

输出应该像

------------------------------------
id | subject | Time1 | Time2| Time3
------------------------------------
1  | String1 | 50    |  78  |  28
2  | String2 | 60    |  99  |  39
3  |         |       |      |

谢谢！

推荐答案

`SELECT 
     id, 
     subject, 
     Time1, 
     Time2, 
     IF( Time1 != '' AND Time2 != '', Time2-Time1, '') as Time3 
FROM tbl_time`

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