using "if" and "else" Stored Procedures MySQL

The problem is you either haven't closed your if or you need an elseif:

create procedure checando(    in nombrecillo varchar(30),    in contrilla varchar(30),     out resultado int)begin     if exists (select * from compas where nombre = nombrecillo and contrasenia = contrilla) then        set resultado = 0;    elseif exists (select * from compas where nombre = nombrecillo) then        set resultado = -1;    else         set resultado = -2;    end if;end;

I think that this construct: if exists (select... is specific for MS SQL. In MySQL EXISTS predicate tells you whether the subquery finds any rows and it's used like this: SELECT column1 FROM t1 WHERE EXISTS (SELECT * FROM t2);

You can rewrite the above lines of code like this:

DELIMITER $$CREATE PROCEDURE `checando`(in nombrecillo varchar(30), in contrilla varchar(30), out resultado int)BEGIN    DECLARE count_prim INT;    DECLARE count_sec INT;    SELECT COUNT(*) INTO count_prim FROM compas WHERE nombre = nombrecillo AND contrasenia = contrilla;    SELECT COUNT(*) INTO count_sec FROM FROM compas WHERE nombre = nombrecillo;    if (count_prim > 0) then        set resultado = 0;    elseif (count_sec > 0) then        set resultado = -1;    else         set resultado = -2;    end if;    SELECT resultado;END

you can use CASE WHEN as follow as achieve the as IF ELSE.

SELECT FROM A a LEFT JOIN B b ON a.col1 = b.col1 AND (CASE         WHEN a.col2 like '0%' then TRIM(LEADING '0' FROM a.col2)        ELSE substring(a.col2,1,2)    END)=b.col2; 

p.s:just in case somebody needs this way.