錯誤1066（42000）：不是唯一的表/別名：'mp'在mysql中的外部連接

Question

我有一個問題，將我的informix數據庫轉換爲mysql。 我得到了大部分的事情，但一些功能只是不工作。

這表明了：ERROR 1066（42000）：不是唯一的表/別名： 'MP'

順便說一句，這是舊

CREATE PROCEDURE "informix".mw_getsvid(mwid INT) 
RETURNING INT; 

DEFINE svId INT; 
SELECT sv.ID INTO svId 
    FROM MessWert mw, MessPunkt mp, 
     OUTER (MPZuordnung mpz, SummVorschrift sv) 
    WHERE mw.id = mwid 
     AND mw.messpunktid = mp.id 
     AND mp.id = mpz.messpunktid 
     AND mpz.summvorschriftid = sv.id 
     AND mpz.zeitraum_von <= mw.datendatum 
     AND mpz.zeitraum_bis > mw.datendatum; 

RETURN svId; 

END PROCEDURE; 

將是馬麗娟如果u有一好的想法:) :)

Answer 1

如果你要使用JOIN，你不需要使用FROM子句中的所有表，因爲你做的工作是重複的。如果您要將表放入FROM子句和JOIN中，則應使用不同的別名。你應該這樣做：

DELIMITER // 
CREATE FUNCTION mw_getsvid(mwid INT) RETURNS INT 
BEGIN 
DECLARE svId INT; 
SELECT sv.ID INTO svId 
FROM messwert AS mw 
    LEFT JOIN messpunkt mp ON mw.messpunktid = mp.id 
    LEFT JOIN mpzuordnung mpz ON mp.id = mpz.messpunktid 
    LEFT JOIN summvorschrift sv ON mpz.summvorschriftid = sv.id 
    LEFT JOIN messwert mw ON mpz.zeitraum_von <= mw.datendatum 
    LEFT JOIN messwert mw ON mpz.zeitraum_bis > mw.datendatum; 
UNION ALL 
SELECT sv.ID INTO svId 
FROM messwert AS mw 
    RIGHT JOIN messpunkt mp ON mw.messpunktid = mp.id 
    RIGHT JOIN mpzuordnung mpz ON mp.id = mpz.messpunktid 
    RIGHT JOIN summvorschrift sv ON mpz.summvorschriftid = sv.id 
    RIGHT JOIN messwert mw ON mpz.zeitraum_von <= mw.datendatum 
    RIGHT JOIN messwert mw ON mpz.zeitraum_bis > mw.datendatum; 
RETURN svId; 

END //; 

DELIMITER ;