sql - Postgres 计算条件下的总行数，但忽略限制和分组依据

Question

我有一个看起来像这样的查询:

SELECT t1.id, t1.name, t1.description
FROM t1
LEFT JOIN t2 ON (t2.id = t1.id)
WHERE condition
GROUP BY t1.id
LIMIT 100

除了返回指定的列(id、名称、描述)之外，我还想计算超过限制的满足此查询的总行数。问题是，由于 GROUP BY，如果我要进行计数 (*)，我只会得到一堆带有 1 的行。

所以我的问题是:如何计算此查询返回的行数？我怎么能不考虑限制呢？

是否可以在单个查询中同时返回行数和列数据？还是我需要使用两个查询？

Answer 1

你可以使用子查询:

SELECT COUNT(*)
FROM (
  SELECT t1.id
  FROM t1
  LEFT JOIN t2 ON (t2.id = t1.id)
  WHERE condition
  GROUP BY t1.id) sub

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编辑:

Also is it possible to return both the row count AND the column data in a single query? Or would I need to use two queries?

是的，使用窗口化 COUNT:

SELECT t1.id, COUNT(*) OVER() AS num_of_r0ws
FROM t1
LEFT JOIN t2 ON (t2.id = t1.id)
WHERE condition
GROUP BY t1.id