如何根据条件为空或不为空选择数据mysql 5.7

Question

我 table 像这样叫 my_table

+------------+-------+-------+
|  product   | type1 | type2 |
+------------+-------+-------+
| Banana     | NULL  | A1    |
| Grape      | NULL  | B1    |
| Watermelon | A     | A1    |
| Orange     | B     | A1    |
+------------+-------+-------+

我想select根据他的类型做产品，如果type1为NULL则使用type 2，如果不是则使用type 1

所以预期的结果是这样的

+------------+------+
|  product   | type |
+------------+------+
| Banana     | A1   |
| Grape      | B1   |
| Watermelon | A    |
| Orange     | B    |
+------------+------+

Answer 1

使用COALESCE:

SELECT
    product,
    COALESCE(type1, type2) AS type
FROM yourTable;

COALESCE(a, b) 函数将 return a，如果它不是 NULL，否则它会退回到 returning b .

如何根据条件为空或不为空选择数据mysql 5.7

how to selected data based on condition null or not null mysql 5.7

mysql

mysql-select-db