How to Assign the Result of a Dynamic Query to an OUT Parameter in a MySQL Stored Procedure?

Dynamic Query Execution and Output Assignment in MySQL Stored Procedure

In MySQL, it is possible to dynamically generate and execute queries within a stored procedure. However, to assign the result of a dynamic query to an OUT parameter, a slightly different approach is needed.

Consider the stored procedure code provided in the question:

CREATE PROCEDURE 'searchInvoice'
(
  OUT numOfRecords INT
)
BEGIN
  DECLARE query1 TEXT; 
  DECLARE query2 TEXT; 

 SET query1 = 'SELECT COUNT(*) bla bla bla.....'; 
 // Query1 to select the count of matching tuples..

 SET query2 = 'SELECT * from bla bla bla....';
 // Query2 to select original records...

 // later part of this both queries generate dynamically according to some IN parameters..

 // now I wanna assign the output of the query1 into numOfRecords 
 // and I wanna execute the query2 as well.. like this

    SET @Sql = query2;        
    PREPARE STMT FROM @Sql; 
    EXECUTE STMT; 
    DEALLOCATE PREPARE STMT;

 // output of the query2 can be read in PHP

END

To assign the output of query1 to the numOfRecords OUT parameter, the following steps can be taken:

1. Create user-defined variables to store the results:

SET @numOfRecords = 0;

2. Prepare and execute the dynamic query using a cursor:

DECLARE query1Cursor CURSOR FOR query1;
OPEN query1Cursor;
FETCH query1Cursor INTO @numOfRecords;
CLOSE query1Cursor;

3. Update the OUT parameter with the assigned value:

SET numOfRecords = @numOfRecords;

With this modified approach, the stored procedure can both execute dynamic queries and assign the output of specific queries to OUT parameters.

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