Is it possible to set an user variable based on the result of a query in MySQL?
What I want to achieve is something like this (we can assume that both USER and GROUP are unique):
set @user = 123456;
set @group = select GROUP from USER where User = @user;
select * from USER where GROUP = @group;
Please note that I know it's possible but I do not wish to do this with nested queries.
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Yes, but you need to move the variable assignment into the query:
SET @user := 123456;
SELECT @group := `group` FROM user WHERE user = @user;
SELECT * FROM user WHERE `group` = @group;
Test case:
CREATE TABLE user (`user` int, `group` int);
INSERT INTO user VALUES (123456, 5);
INSERT INTO user VALUES (111111, 5);
Result:
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)
Note that for SET, either = or := can be used as the assignment operator. However inside other statements, the assignment operator must be := and not = because = is treated as a comparison operator in non-SET statements.
UPDATE:
Further to comments below, you may also do the following:
SET @user := 123456;
SELECT `group` FROM user LIMIT 1 INTO @group;
SELECT * FROM user WHERE `group` = @group;
Just add parenthesis around the query:
set @user = 123456;
set @group = (select GROUP from USER where User = @user);
select * from USER where GROUP = @group;
Use this way so that result will not be displayed while running stored procedure.
The query:
SELECT a.strUserID FROM tblUsers a WHERE a.lngUserID = lngUserID LIMIT 1 INTO @strUserID;
First lets take a look at how can we define a variable in mysql
To define a varible in mysql it should start with '@' like @{variable_name} and this '{variable_name}', we can replace it with our variable name.
Now, how to assign a value in a variable in mysql. For this we have many ways to do that
Example :-
mysql > SET @a = 1;
Example:-
mysql > @a:=1;
Example:-
mysql > select 1 into @a;
Here @a is user defined variable and 1 is going to be assigned in @a.
Now how to get or select the value of @{variable_name}.
we can use select statement like
Example :-
mysql > select @a;
it will show the output and show the value of @a.
Now how to assign a value from a table in a variable.
For this we can use two statement like :-
1.
@a := (select emp_name from employee where emp_id = 1);
select emp_name into @a from employee where emp_id = 1;
Always be careful emp_name must return single value otherwise it will throw you a error in this type statements.
refer this:- http://www.easysolutionweb.com/sql-pl-sql/how-to-assign-a-value-in-a-variable-in-mysql
Source: Stackoverflow.com