Question

我阅读了问题Combine multiple rows into one row MySQL，该问题展示了如何使用单行从 SELECT 语句的多行中获取结果。 SQL Fiddle with Demo也运行正常。在该问题中，有两个表： t1 和 t2 。我的问题有三个表，我已经简化了这个问题：

表语言：

ID              INT(11)         NOT NULL    PRIMARY_KEY
name            VARCHAR(255)    NOT NULL    UNIQUE

表 languages_have_persons ：

Languages_ID    INT(11)         NOT NULL    PRIMARY_KEY
Persons_ID  INT(11)             NOT NULL

表人：

ID              INT(11)         NOT NULL    PRIMARY_KEY
firstName       VARCHAR(255)    NOT NULL
lastName        VARCHAR(255)    NOT NULL

我想要做的是将这些表类似地组合起来，但是我现在几个小时都没有这样做。这是我的最后一次尝试：

SELECT p1.ID
    , p1.firstName
    , p1.lastName
    CONCAT_WS(', '
        , l2de.name
        , l2en.name
    )
    FROM
        languages_have_persons AS lp, persons AS p1
    LEFT JOIN languages AS l2de ON
        l2de.ID = 4 -- German
    LEFT JOIN languages AS l2en ON
        l2en.ID = 5 -- English
WHERE p1.ID = lp.Persons_ID
ORDER BY lastName, firstName;

错误消息显示为：

Fehler
SQL-Befehl: Dokumentation


SELECT p1.ID AS ID
    , p1.firstName AS firstName
    , p1.lastName AS lastName
    CONCAT_WS(', '
        , l2de.name
        , l2en.name
    )
    FROM
        languages_have_persons AS lp, persons AS p1
    LEFT JOIN languages AS l2de ON
        l2de.ID = 4     LEFT JOIN languages AS l2en ON
        l2en.ID = 5 WHERE p1.ID = lp.Persons_ID
ORDER BY lastName, firstName LIMIT 0, 25
MySQL meldet: Dokumentation

#1064 - Fehler in der SQL-Syntax. Bitte die korrekte Syntax im Handbuch
nachschlagen bei '(', '
        , l2de.name
        , l2en.name
    )
    FROM
        languages_have_persons AS lp, ' in Zeile 4

我也尝试过其他方法，但没有一种方法具有正确的语法。我想要的结果如下：

表语言：

ID    name
4     German
5     English

表 language_have_persons ：

Languages_ID    Persons_ID    
    4                2
    5                1
    5                2

表人：

ID    firstName    lastName
1     Joe           Frazier
2     Arnold        Schwarzenegger

我对正确的SELECT语句的期望是

firstName    lastName           CONCAT_WS(…
Joe           Frazier           English
Arnold        Schwarzenegger    German, English

您是否在上面的SQL语法中看到错误？如果没有，你知道如何解决它吗？

感谢您的帮助！

Answer 1

SELECT p1.ID
    , p1.firstName
    , p1.lastName,<--------------------I had made change at this line
    CONCAT_WS(', '
        , l2de.name
        , l2en.name
    )
    FROM
        languages_have_persons AS lp, persons AS p1
    LEFT JOIN languages AS l2de ON
        l2de.ID = 4 -- German
    LEFT JOIN languages AS l2en ON
        l2en.ID = 5 -- English
WHERE p1.ID = lp.Persons_ID
ORDER BY lastName, firstName;

或者，您可以在下面尝试进一步查询。

SELECT p1.ID
    , p1.firstName
    , p1.lastName,
    l2de.name
    FROM
    persons p1
    INNER JOIN languages_have_persons lp on p1.ID=lp.Persons_ID 
    INNER JOIN language l2de on l2de.ID=lp.Languages_ID 
    WHERE l2de.ID  IN(4,5)
    ORDER BY lastName, firstName;

您可以尝试以上查询。

Answer 2

在另一个网站上，我进行了另一次讨论，同事找到了解决方案，即

SELECT DISTINCT pl.ID
    , firstName
    , lastName
    , languages
FROM persons p
    , ( SELECT
        lp.Persons_ID AS ID,
        GROUP_CONCAT(DISTINCT l.name) AS languages
    FROM languages l
        , languages_have_persons lp
    WHERE l.id = lp.Languages_ID
    GROUP BY lp.Persons_ID
    ) AS pl
WHERE p.id = pl.id
ORDER BY p.id;

所以，问题是正确的答案。

在MySQL

2 个答案: