SELECT INTO Variable in MySQL DECLARE causes syntax error?

Question

I´d like to SELECT a single value into a variable. I´d tried to following:

DECLARE myvar INT(4);

-- immediately returns some syntax error.<

Answer 1

You don't need to DECLARE a variable in MySQL. A variable's type is determined automatically when it is first assigned a value. Its type can be one of: integer, decimal, floating-point, binary or nonbinary string, or NULL value. See the User-Defined Variables documentation for more information:

http://dev.mysql.com/doc/refman/5.0/en/user-variables.html

You can use SELECT ... INTO to assign columns to a variable:

http://dev.mysql.com/doc/refman/5.0/en/select-into-statement.html

Example:

mysql> SELECT 1 INTO @var;
Query OK, 1 row affected (0.00 sec)

mysql> SELECT @var;
+------+
| @var |
+------+
| 1    |
+------+
1 row in set (0.00 sec)

Answer 2

SELECT c1, c2, c3, ... INTO @v1, @v2, @v3,... FROM table_name WHERE condition;

Answer 3

I ran into this same issue, but I think I know what's causing the confusion. If you use MySql Query Analyzer, you can do this just fine:

SELECT myvalue 
INTO @myvar 
FROM mytable 
WHERE anothervalue = 1;

However, if you put that same query in MySql Workbench, it will throw a syntax error. I don't know why they would be different, but they are. To work around the problem in MySql Workbench, you can rewrite the query like this:

SELECT @myvar:=myvalue
FROM mytable
WHERE anothervalue = 1;

Answer 4

In the end a stored procedure was the solution for my problem. Here´s what helped:

DELIMITER //
CREATE PROCEDURE test ()
  BEGIN
  DECLARE myvar DOUBLE;
  SELECT somevalue INTO myvar FROM mytable WHERE uid=1;
  SELECT myvar;
  END
  //

DELIMITER ;

call test ();

Answer 5

You can also use SET instead of DECLARE

SET @myvar := (SELECT somevalue INTO myvar FROM mytable WHERE uid=1);

SELECT myvar;

Answer 6

For those running in such issues right now, just try to put an alias for the table, this should the trick, e.g:

SELECT myvalue 
  INTO myvar 
  FROM mytable x
 WHERE x.anothervalue = 1;

It worked for me.

Cheers.