使用"if"和"else"存储过程MySQL

Question

我在尝试创建这个存储过程时遇到了一些困难,欢迎任何形式的帮助:

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;
else if exists (select * from compas where nombre = nombrecillo) then
    set resultado = -1;
else 
    set resultado = -2;
end if;
end;

我正在研究的表是:

+-------------+-------------+------+-----+---------+-------+
| Field       | Type        | Null | Key | Default | Extra |
+-------------+-------------+------+-----+---------+-------+
| Nombre      | varchar(30) | YES  |     | NULL    |       |
| contrasenia | varchar(30) | YES  |     | NULL    |       |
+-------------+-------------+------+-----+---------+-------+

Answer 1

问题是你要么没有关闭你,if要么你需要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;

Answer 2

我认为这个结构:if exists (select...特定于MS SQL.在MySQL EXISTS谓词中告诉您子查询是否找到任何行,并且它的使用方式如下:SELECT column1 FROM t1 WHERE EXISTS (SELECT * FROM t2);

您可以像这样重写上面的代码行:

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