为什么我的集合返回函数的列在 PostgreSQL 查询中使用时会串联起来，如何解决这个问题？

从函数返回的记录中的串联列

尝试在另一个查询中使用集合返回函数执行查询时会出现此问题，导致所有函数返回列被连接成一列。

函数声明

以下 Postgres 函数 account_servicetier_for_day 接受帐户 ID 和日期并返回历史数据：

CREATE OR REPLACE FUNCTION account_servicetier_for_day(_accountid integer, _day timestamp without time zone) RETURNS setof account_dsl_history_info AS
$BODY$
DECLARE _accountingrow record;
BEGIN
  Return Query
  Select * From account_dsl_history_info
  Where accountid = _accountid And timestamp <= _day + interval '1 day - 1 millisecond'
  Order By timestamp Desc 
  Limit 1;
END;
$BODY$ LANGUAGE plpgsql;

问题：串联列

当函数为直接执行，它返回带有单独列的预期结果。但是，在查询中使用时，列会连接成一个：

Select
    '2014-08-12' As day, 0 As inbytes, 0 As outbytes, acct.username, acct.accountid, acct.userid,
    account_servicetier_for_day(acct.accountid, '2014-08-12')
From account_tab acct
Where acct.isdsl = 1
    And acct.dslservicetypeid Is Not Null
    And acct.accountid Not In (Select accountid From dailyaccounting_tab Where Day = '2014-08-12')
Order By acct.username

解决方案：SQL 分解

要将函数返回的记录分解为各个列，请使用 SQL 语法：

SELECT * FROM account_servicetier_for_day(20424, '2014-08-12');

Postgres 9.3 或更高版本

对于Postgres 9.3 及更高版本，可以使用 JOIN LATERAL 重写查询：

SELECT '2014-08-12' AS day, 0 AS inbytes, 0 AS outbytes
     , a.username, a.accountid, a.userid
     , f.*   -- but avoid duplicate column names!
FROM   account_tab a
     , account_servicetier_for_day(a.accountid, '2014-08-12') f  -- <-- HERE
WHERE  a.isdsl = 1
AND    a.dslservicetypeid IS NOT NULL
AND    NOT EXISTS (
   SELECT FROM dailyaccounting_tab
   WHERE  day = '2014-08-12'
   AND    accountid = a.accountid
   )
ORDER  BY a.username;

Postgres 9.2 或更早版本

对于 Postgres 9.2 或更早版本，使用子查询调用 set-returning 函数并分解外部查询中的记录：

SELECT '2014-08-12' AS day, 0 AS inbytes, 0 AS outbytes
     , a.username, a.accountid, a.userid
     , (a.rec).*   -- but be wary of duplicate column names!
FROM  (
   SELECT *, account_servicetier_for_day(a.accountid, '2014-08-12') AS rec
   FROM   account_tab a
   WHERE  a.isdsl = 1
   AND    a.dslservicetypeid Is Not Null
   AND    NOT EXISTS (
       SELECT FROM dailyaccounting_tab
       WHERE  day = '2014-08-12'
       AND    accountid = a.accountid
      )
   ) a
ORDER  BY a.username;

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