如何在同一个表中获取列的总和然后使用sql在2个表之间的差异

Question

如何有两个表

1.doner_record - ＆GT;

Id| doner_id|blood_group | units |status|
1 |       1       |A                    | 3        |0         |
2 |        3      |B                    | 2        |0         |
3 |        2      |A                    | 1        |0         |
4 |        1      |A                    | 2        |0         |

2。接受者

Id| name        |blood_group | units |status|
1 |       ayush  |A                    | 1        |0         |
2 |       akash  |B                    | 2        |0         |
3 |        Hari     |A                   | 1        |0         |
4 |        Ram    |A                   | 1        |0         |

如何使用sql

获取血型库存

|blood_group | units |
|A                    | 3        |
|B                    | 0        |

Answer 1

对于Stocked Blood of Blood，您需要从接受的单位总和中检查左侧单位。

检查此查询可能会得到结果：

select blood_group,(ifnull(t1.unit,0) - ifnull(t2.unit,0)) as StockedUnit  from 
(select blood_group,sum(unit) unit from 
doner_record group by blood_group) t1
left outer join
(select blood_group,sum(unit) unit from 
acceptors group by blood_group) t2

on t1.blood_group = t2.blood_group