在SQL中映射值选择？

Question

我有一个表,让我们为简单起见称之为Plant,有三列:id,name,category.
这是最简化的例子,所以请不要担心规范化......

+-------+--------+------------+
| id    | name   | category   |
+-------+--------+------------+
| 1     | orange | fruits     |
| 2     | banana | fruits     |
| 3     | tomato | vegetables |
| 4     | kaokao | NULL       |
+-------+--------+------------+

如果想要一个返回的查询:

• ' Fruit Plant'而不是' fruits'
• ' Vegetable Plant'而不是' vegetables'
• ' unknown'而不是NULLs

所以回报应该是:

+-------+--------+-----------------+
| id    | name   | category        |
+-------+--------+-----------------+
| 1     | orange | Fruit Plant     |
| 2     | banana | Fruit Plant     |
| 3     | tomato | Vegetable Plant |
| 4     | kaokao | unknown         |
+-------+--------+-----------------+

如何为选择值执行此映射？

我正在使用mysql,如果这可能IF在mysql中有一个特殊的关键字/函数

Answer 1

你可以使用case表达式:

select
    id,
    name,
    case 
        when category = 'fruits' then 'Fruit Plant'
        when category = 'vegetables' then 'Vegetable Plant'
        when category is null then 'unknown'
    end as category
from Plant

Answer 2

使用 case功能（带有else语句）：

SELECT id, name, 
CASE category
 WHEN 'vegetables' THEN 'Vegetable Plant'
 WHEN 'fruits' THEN 'Fruit Plant'
 WHEN IS NULL THEN 'unknown'
 ELSE 'default values'
END
FROM Plant