如何在SQL中将数据表列值转换为CSV格式？

根据不同SQL数据库类型，以下是实现列值转CSV的常用方法：

MySQL/MariaDB #

使用GROUP_CONCAT()函数聚合列值：

SELECT 
    ID,
    GROUP_CONCAT(Name SEPARATOR ',') AS Name_CSV
FROM your_table
GROUP BY ID;

需要去除重复值时，可添加DISTINCT：

SELECT 
    ID,
    GROUP_CONCAT(DISTINCT Name SEPARATOR ',') AS Name_CSV
FROM your_table
GROUP BY ID;

PostgreSQL #

使用STRING_AGG()函数，支持排序：

SELECT 
    ID,
    STRING_AGG(Name, ',' ORDER BY Name) AS Name_CSV
FROM your_table
GROUP BY ID;

去重写法：

SELECT 
    ID,
    STRING_AGG(DISTINCT Name, ',' ORDER BY Name) AS Name_CSV
FROM your_table
GROUP BY ID;

SQL Server #

2017及以上版本直接用STRING_AGG()：

SELECT 
    ID,
    STRING_AGG(Name, ',') WITHIN GROUP (ORDER BY Name) AS Name_CSV
FROM your_table
GROUP BY ID;

旧版本可通过FOR XML PATH实现：

SELECT 
    DISTINCT ID,
    STUFF((
        SELECT ',' + Name 
        FROM your_table t2 
        WHERE t2.ID = t1.ID 
        ORDER BY Name
        FOR XML PATH(''), TYPE
    ).value('.', 'NVARCHAR(MAX)'), 1, 1, '') AS Name_CSV
FROM your_table t1;

Oracle #

使用LISTAGG()函数：

SELECT 
    ID,
    LISTAGG(Name, ',') WITHIN GROUP (ORDER BY Name) AS Name_CSV
FROM your_table
GROUP BY ID;

去重需结合子查询：

SELECT 
    ID,
    LISTAGG(Name, ',') WITHIN GROUP (ORDER BY Name) AS Name_CSV
FROM (SELECT DISTINCT ID, Name FROM your_table)
GROUP BY ID;

内容的提问来源于stack exchange，提问作者Raunak