Mysql group_concat函数列转行，与行转列

    CREATE TABLE digits (digit INT(1));
    INSERT INTO digits
    VALUES
        (0),
        (1),
        (2),
        (3),
        (4),
        (5),
        (6),
        (7),
        (8),
        (9);
    CREATE TABLE sequence (seq INT(3));
    INSERT INTO sequence (
        SELECT
            D1.digit + D2.digit * 10
        FROM
            digits D1
        CROSS JOIN digits D2
    );

配置表sequence的结果为0-99的一列数字：

SQL：

SELECT
    SUBSTRING_INDEX(
        SUBSTRING_INDEX(JoinEventIds, ‘,‘, seq),
        ‘,‘ ,- 1
    ) JoinEventIds
FROM
    sequence
CROSS JOIN user
WHERE
    seq BETWEEN 1
AND (
    SELECT
        1 + LENGTH(JoinEventIds) - LENGTH(
            REPLACE (JoinEventIds, ‘,‘, ‘‘)
        )
)

方法二（自己不想建表，图省事）：将sequence替换为SELECT @rownum:=@rownum+1 AS seq FROM (SELECT @rownum:=0) r, user  LIMIT 0,100) ，user为表名，这张表需要大于100条。

SELECT  SUBSTRING_INDEX(
            SUBSTRING_INDEX(JoinEventIds, ‘,‘, seq),
            ‘,‘ ,- 1
        ) JoinEventIds
    FROM
        (SELECT @rownum:=@rownum+1 AS seq FROM (SELECT @rownum:=0) r, user  LIMIT 0,100) b
    CROSS JOIN user
    WHERE
        seq BETWEEN 1
    AND (
        SELECT
            1 + LENGTH(JoinEventIds) - LENGTH(REPLACE(JoinEventIds, ‘,‘, ‘‘))) 

两种方法结果均为：

Mysql group_concat函数列转行，与行转列

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