How to Set User Variables from Query Results in MySQL?

Setting User Variables from Query Results in MySQL

It is possible to populate user variables with the output of a query in MySQL. To achieve this, incorporate the variable assignment within the query itself. For example:

<code class="mysql">SET @user := 123456;
SELECT @group := `group` FROM user WHERE user = @user;
SELECT * FROM user WHERE `group` = @group;</code>

Test this by creating a table:

<code class="mysql">CREATE TABLE user (`user` int, `group` int);
INSERT INTO user VALUES (123456, 5);
INSERT INTO user VALUES (111111, 5);</code>

The resulting output demonstrates how the user variable @group is populated with the appropriate group ID:

<code class="mysql">SET @user := 123456;
SELECT @group := `group` FROM user WHERE user = @user;
SELECT * FROM user WHERE `group` = @group;

+--------+-------+
| user   | group |
+--------+-------+
| 123456 |     5 |
| 111111 |     5 |
+--------+-------+
2 rows in set (0.00 sec)</code>

Note: You can use either = or : = as the assignment operator in SET statements. However, in other contexts, only : = should be used as = is a comparator in those instances.

Update:

An alternative approach is to utilize the LIMIT clause:

<code class="mysql">SET @user := 123456;
SELECT `group` FROM user LIMIT 1 INTO @group;
SELECT * FROM user WHERE `group` = @group;</code>

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