从函数返回的记录具有串联的列 [英] Record returned from function has columns concatenated

问题描述

我有一个表，用于存储帐户随时间的变化.如果这些记录尚不存在，我需要将其与另外两个表结合起来以创建特定日期的一些记录.

I have a table which stores account changes over time. I need to join that up with two other tables to create some records for a particular day, if those records don't already exist.

为使事情变得容易(我希望)，我将返回正确历史数据的查询封装到一个接受帐户ID和日期的函数中.

To make things easier (I hope), I've encapsulated the query that returns the correct historical data into a function that takes in an account id, and the day.

如果执行"Select * account_servicetier_for_day(20424, '2014-08-12')"，则会得到预期的结果(该函数返回的所有数据都在单独的列中).如果在另一个查询中使用该函数，则会将所有列合并为一个:

If I execute "Select * account_servicetier_for_day(20424, '2014-08-12')", I get the expected result (all the data returned from the function in separate columns). If I use the function within another query, I get all the columns joined into one:

("2014-08-12 14:20:37",hollenbeck,691,12129,20424,69.95,"2Mb/1Mb 20GB Limit",2048,1024,20.000)

我正在使用"x86_64-slackware-linux-gnu上的PostgreSQL 9.2.4，由gcc(GCC)4.7.1，64位编译".

I'm using "PostgreSQL 9.2.4 on x86_64-slackware-linux-gnu, compiled by gcc (GCC) 4.7.1, 64-bit".

查询:

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

功能:

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;

推荐答案

通常，分解从函数返回的行并获取单个列:

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

关于查询:

具有JOIN LATERAL的清洁器:

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 1
   FROM   dailyaccounting_tab
   WHERE  day = '2014-08-12'
   AND    accountid = a.accountid
   )
ORDER  BY a.username;

LATERAL关键字在这里是隐式的，函数始终可以引用更早的FROM项. 手册:

The LATERAL keyword is implicit here, functions can always refer earlier FROM items. The manual:

LATERAL也可以在函数调用FROM项之前，但是在此 情况下它是一个干扰词，因为函数表达式可以引用 在任何情况下都是较早的FROM项目.

LATERAL can also precede a function-call FROM item, but in this case it is a noise word, because the function expression can refer to earlier FROM items in any case.

相关:

• 插入一个表中的多个行基于另一个表中的数字

在FROM列表中带有逗号的缩写表示法(通常)等效于CROSS JOIN LATERAL(与[INNER] JOIN LATERAL ... ON TRUE相同)，因此从结果中删除了行，其中函数调用不返回任何行.要保留此类行，请使用 LEFT JOIN LATERAL ... ON TRUE :

The short notations with a comma in the FROM list is (mostly) equivalent to a CROSS JOIN LATERAL (same as [INNER] JOIN LATERAL ... ON TRUE) and thus removes rows from the result where the function call returns no row. To retain such rows, use LEFT JOIN LATERAL ... ON TRUE:

...
FROM  account_tab a
LEFT  JOIN LATERAL account_servicetier_for_day(a.accountid, '2014-08-12') f ON TRUE
...

此外，在可以避免使用时不要使用NOT IN (subquery).这是几种方法中最慢，最棘手的:

Also, don't use NOT IN (subquery) when you can avoid it. It's the slowest and most tricky of several ways to do that:

• 选择在其他表格

我建议使用NOT EXISTS.

您可以在SELECT列表中调用返回集合的函数(这是标准SQL的Postgres扩展).出于性能原因，最好在子查询中完成此操作.在外部查询中分解(众所周知的！)行类型，以避免重复评估该函数:

You can call a set-returning function in the SELECT list (which is a Postgres extension of standard SQL). For performance reasons, this is best done in a subquery. Decompose the (well-known!) row type in the outer query to avoid repeated evaluation of the function:

SELECT '2014-08-12' AS day, 0 AS inbytes, 0 AS outbytes
     , a.username, a.accountid, a.userid
     , (a.rec).*   -- but avoid 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 1
       FROM   dailyaccounting_tab
       WHERE  day = '2014-08-12'
       AND    accountid = a.accountid
      )
   ) a
ORDER  BY a.username;

克雷格·林格(Craig Ringer)给出的相关答案以及解释，为什么我们最好在外部查询中分解:

Related answer by Craig Ringer with an explanation, why we better decompose in the outer query:

• Postgres 10 最终在SELECT列表中重新实现了集返回功能，以修复意外的副作用.

  Postgres 10 finally re-implemented set-returning functions in the SELECT list to fix unexpected side effects.

  这篇关于从函数返回的记录具有串联的列的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！