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MySQL - Variables in Stored Programs
You can create user-defined variables or system variables with in Procedures. You can define a variable with in a stored program using the DECLARE statement. You can use these variables outside the stored-program context. These stored programs can also accept parameters.
Declaring the local variables
You can declare a local variable using the DECLARE statement. The value of a variable can be a constant.
Syntax
Following the syntax to do declare a local variable −
DECLARE var_name type [DEFAULT value]
Where, var_name is the name of the variable and type is the datatype of the variable.
Example
Following is an example of declaring local variables in a procedure −
DELIMITER // CREATE PROCEDURE RepeatExample() BEGIN DECLARE val INT; DECLARE squares INT; DECLARE res VARCHAR(100); SET val=1; SET squares=1; SET res = ''; REPEAT SET squares = val*val; SET res = CONCAT(res, squares,','); SET val = val + 1; UNTIL val >= 10 END REPEAT; SELECT res; END// DELIMITER ;
You can call the above procedure as follows −
CALL RepeatExample;
Output
Following is the output of the above program −
res |
---|
1,4,9,16,25,36,49,64,81, |
Accepting values as parameters
The procedures and functions in MySQL accept parameters and you can pass values to these while calling them.
Example
Following query creates a function that accepts parameters −
DELIMITER // CREATE FUNCTION sample(a INT, b INT) RETURNS INT DETERMINISTIC BEGIN declare RES INT; SET RES = a+b; return RES; END// DELIMITER ;
You can call the above function as −
ELECT sample(2258, 6695);
Output
The above query produces the output shown below −
sample(2258, 6695) |
---|
8953 |
Example
Following query creates a procedure that accepts parameters −
DELIMITER // CREATE PROCEDURE sample(IN a INT, IN b INT, OUT RES INT) BEGIN SET RES = a+b; END// DELIMITER ;
You can call the above procedure as −
CALL sample(1254, 5894, @res); SELECT @res;
Output
Following is the output of the above mysql query −
@res |
---|
7148 |
Reading values from queries into local variables
You can read values from a query into a local variable using the INTO clause.
Example
Assume we have created a table named dispatches as shown below −
CREATE TABLE Dispatches( Product_Name VARCHAR(255), Name_Of_Customer VARCHAR(255), Month_Of_Dispatch VARCHAR(255), Price INT, Location VARCHAR(255) );
Let us insert 5 records in it using the INSERT statement.
Insert into dispatches values ('Key-Board', 'Raja', TIMESTAMP('2019-05-04', '15:02:45'), 7000, 'Hyderabad'), ('Earphones', 'Roja', TIMESTAMP('2019-06-26', '14:13:12'), 2000, 'Vishakhapatnam'), ('Mouse', 'Puja', TIMESTAMP('2019-12-07', '07:50:37'), 3000, 'Vijayawada'), ('Mobile', 'Vanaja' , TIMESTAMP ('2018-03-21', '16:00:45'), 9000, 'Chennai'), ('Headset', 'Jalaja' , TIMESTAMP('2018-12-30', '10:49:27'), 6000, 'Goa');
Following query creates a procedure that retrieves the Product_Name and location from a SELECT query to local variables. In here we are using two OUT parameters to store these values −
DELIMITER // ; Create procedure proc (OUT name VARCHAR(255), OUT loc VARCHAR(255)) BEGIN SELECT Product_Name, Location into name, loc FROM Dispatches where Name_Of_Customer = 'Roja'; END // DELIMITER ;
You need to call this procedure by passing two variables and you can retrieve values from them using SELECT statement.
CALL proc(@name, @loc); SELECT @name, @loc;
Output
The above mysql query will generate the following output −
@name | @loc |
---|---|
Earphones | Vishakhapatnam |
Setting values directly
You can also set values to the variables in MySQL directly using the SET statement.
Example
Following query creates a procedure in here we have declared two variables and assigned values to these using the SET statement −
DELIMITER // CREATE PROCEDURE RepeatExample() BEGIN DECLARE val INT; DECLARE squares INT; DECLARE res VARCHAR(100); SET val=1; SET squares=1; SET res = ''; REPEAT SET squares = val*val; SET res = CONCAT(res, squares,','); SET val = val + 1; UNTIL val >= 10 END REPEAT; SELECT res; END// DELIMITER ;
You can call the above procedure as follows −
CALL RepeatExample; //
Output
Following is the output of the above query −
res |
---|
1,4,9,16,25,36,49,64,81, |
Scope and resolution of the local variables
The scope of the local variables lies within the block (BEGIN...END) it I declared. If you have nested block statements the internal block can use the variable declared in the external block.
If you create a Prepared statement in a Procedure or a function it cannot use a local variable.
The local variable's name should be different from any of the table's columns (returned by the query) used in the current stored program.
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