Mapping values in SQL select?

Question

I have a table, lets for simplicity call it Plant , with three columns: id , name , category .
This the most simplified example, so please do not worry about normalization ...

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

If want to have a query which returns:

• ' Fruit Plant ' instead of ' fruits '
• ' Vegetable Plant ' instead of ' vegetables '
• ' unknown ' instead of NULL s

So the return should be:

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

How can I do this mapping for select values ?

I am using mysql, if this may have a special IF keyword/function in mysql

Answer 1

You can use case expression:

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

use case function (with else statement for default values) :

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

Answer 3

Try it:

SELECT
  `id`,
  `name`,
  CASE
    WHEN `category` = 'fruits' THEN 'Fruit Plant'
    WHEN `category` = 'vegetables' THEN 'Vegetable Plant'
    WHEN `category` = NULL THEN 'unknown'
    ELSE `category`
  END 
  AS `category`
FROM `Plant`