mysql中存储过程中的EXISTS和输出参数

Question

Here is my stored procedure for returning true if any data is found in document details but it generates an error

" #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '@result = true end if end' at line 5"

create procedure abcde(out result boolean)
    begin

        if exists(select * from document_details)
        then @result = true;
        end if
    end

Kindly,provide me a solution asap

Answer 1

Besides the fact that you need to use SET to assign a value to a local variable or a parameter, there are other things worth mentioning

1. you have to have a semicolon after END IF
2. since EXSITS() returns BOOLEAN you can just directly assign it to your OUT parameter

That being said your stored procedure might look like

CREATE PROCEDURE abcde(OUT result BOOLEAN)
  SET result = 
  (
    EXISTS(SELECT * 
             FROM document_details)
  );

Note: now it's just one statement. Therefore you don't even need to change DELIMITER and use BEGIN ... END block.

Here is SQLFiddle demo