从表1连接表2中选择id，table1.column1 + table2.column2作为总数。 如果table2.column2没有值怎么办？

Question

help. T_T

table 1

+---------------+---------+-------------------+
| allowances_id | desc_id | column1           |
+---------------+---------+-------------------+
|             1 |       1 | 64055.35594866848 |
|             2 |       4 | 55627.97197247496 |
|             3 |       6 | 55627.97197247496 |
|             4 |       7 | 55627.97197247496 |
|             5 |       8 | 55627.97197247496 |
|             6 |       9 | 55627.97197247496 |
|             7 |       2 | 50293.50333209634 |
+---------------+---------+-------------------+

table 2

+---------+-------+
| desc_id | total |
+---------+-------+
|       1 | 18150 |
|       4 | 18150 |
|       6 | 18150 |
|       7 | 18150 |
|       8 | 18150 |
|       9 | 18150 |
+---------+-------+

i want table1.column1 + table2.total

table1 (desc_id has a value of 2 in table2 desc_id has no value of 2 so basically the result should be column1 + 0.00

Answer 1

SELECT t1.column1 + COALESCE(t2.column2, 0)
FROM table1 t1
LEFT JOIN table2 t2
    ON t1.id = t2.id

Answer 2

Seems like I miss understood. If you have explicitly added not null for the column while creating then the empty and null values should be stored as 0.

Answer 3

如果您认为自己的值也可以为null，则可以在sql中使用ISNULL。

table1.column2 + ISNULL(table2.column2,0)