MySQL条件查询+控制流功能

Question

MySQL: 5.5.15-55 Percona Server (GPL), Release 21.0

I'm trying to grab a value from a table by comparing it to three other values (in order). If the value = 'value1' stop, and use that value, if not compare it to 'value2' and so on.

Pseudo-query:

SELECT value FROM tbl_variable
IF (WHERE object = 'value1')
ELSE IF (WHERE object = 'value2')
ELSE (WHERE object = 'default');

I think I need to use a Control Flow Function (Case maybe?), but I'm having issues understanding the syntax.

EDIT

Table structure

| Field       | Type             | Null | Key | Default | Extra          |
+-------------+------------------+------+-----+---------+----------------+
| id          | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| var_name    | varchar(50)      | NO   |     |         |                |
| object      | varchar(102)     | YES  | MUL | NULL    |                |
| value       | text             | NO   |     | NULL    |                |

Final query based on Green Demon's answer.

SELECT (CASE 
WHEN object = 'value1' THEN value
WHEN object = 'value2' THEN value 
WHEN object = 'default' THEN value 
END)
AS value
FROM tbl_variables
WHERE value IS NOT NULL
AND var_name = 'NAME'
LIMIT 1;

Answer 1

CASE is pretty much the "switch" function of java and c++, which is the "if" statement for comparing the same object against multiple variables. .

Try this:

SELECT CASE object WHEN 'value1' THEN 'value1'  
WHEN  'value2' THEN 'value2' 
ELSE 'value3' END; 

Alternatively, CASE can be used as the "IF" function

SELECT CASE WHEN object = 'value1' THEN 'value1'  
WHEN  object = 'value2' THEN 'value2' 
ELSE 'value3' END; 

EDIT 1: try

SELECT (CASE WHEN object = 'value1' THEN 'value1'  
WHEN  object = 'value2' THEN 'value2' 
ELSE 'value3' END)  AS returnVal
WHERE returnVal IS NOT NULL

LIMIT 1

;

The first condition returns only values that are not null, and limit 1 says to stop at first valid record.