如何在SQL Server中复制Oracle的LISTAGG函数？

在SQL Server中模拟Oracle的LISTAGG函数

SQL Server自身并不包含LISTAGG函数，但可以通过多种方法实现类似的功能。

MySQL

<code class="language-sql">SELECT
  FieldA,
  GROUP_CONCAT(FieldB ORDER BY FieldB SEPARATOR ',') AS FieldBs
FROM
  TableName
GROUP BY
  FieldA
ORDER BY
  FieldA;</code>

Oracle & DB2

<code class="language-sql">SELECT
  FieldA,
  LISTAGG(FieldB, ',') WITHIN GROUP (ORDER BY FieldB) AS FieldBs
FROM
  TableName
GROUP BY
  FieldA
ORDER BY
  FieldA;</code>

PostgreSQL

<code class="language-sql">SELECT
  FieldA,
  STRING_AGG(FieldB, ',' ORDER BY FieldB) AS FieldBs
FROM
  TableName
GROUP BY
  FieldA
ORDER BY
  FieldA;</code>

SQL Server

SQL Server >= 2017 & Azure SQL

<code class="language-sql">SELECT
  FieldA,
  STRING_AGG(FieldB, ',') WITHIN GROUP (ORDER BY FieldB) AS FieldBs
FROM
  TableName
GROUP BY
  FieldA
ORDER BY
  FieldA;</code>

SQL Server (其他版本)

为了代码的可读性和可维护性，这里使用公用表表达式 (CTE)：

<code class="language-sql">WITH CTE_TableName AS (
  SELECT
    FieldA,
    FieldB
  FROM
    TableName
)
SELECT
  t0.FieldA,
  STUFF(
    (
      SELECT
        ',' + t1.FieldB
      FROM
        CTE_TableName t1
      WHERE
        t1.FieldA = t0.FieldA
      ORDER BY
        t1.FieldB
      FOR XML PATH('')
    ),
    1,
    LEN(','),
    ''
  ) AS FieldBs
FROM
  CTE_TableName t0
GROUP BY
  t0.FieldA
ORDER BY
  FieldA;</code>

SQLite

需要排序时，需使用CTE或子查询

<code class="language-sql">WITH CTE_TableName AS (
  SELECT
    FieldA,
    FieldB
  FROM
    TableName
  ORDER BY
    FieldA,
    FieldB
)
SELECT
  FieldA,
  GROUP_CONCAT(FieldB, ',') AS FieldBs
FROM
  CTE_TableName
GROUP BY
  FieldA
ORDER BY
  FieldA;</code>

无需排序时

<code class="language-sql">SELECT
  FieldA,
  GROUP_CONCAT(FieldB, ',') AS FieldBs
FROM
  TableName
GROUP BY
  FieldA
ORDER BY
  FieldA;</code>

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