Question

考虑两个表：

Foo:
  id INT,
  name VARCHAR

Bar:
  id INT,
  foo_id INT REFERENCES Foo(id),
  event SET('hit','miss'),
  ts TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP

每个Foo项目可以有多个Bar事件。如何在特定日期时间之后查询拥有条形码事件的Foo项目，但在该日期时间之前没有条形码事件？

例如，考虑：

Foo id=1: hit 2014-01-21 hit 2014-01-22 hit 2014-01-23 Foo id=2: hit 2014-01-17 hit 2014-01-19 hit 2014-01-21 Foo id=3: hit 2014-01-14 hit 2014-01-15 hit 2014-01-18 Foo id=4: hit 2014-01-21 hit 2014-01-22 hit 2014-01-24

我想仅查询2014-01-20之后或之后点击的那些Foo项，因此应返回ID 1和4。

我尝试将Bar表加入到自身中，使用以下几种变体：

SELECT b1.id FROM Bar b1 JOIN Bar b2 using (foo_id) WHERE b1.ts > '2014-01-20';

但是，我没有看到如何用WHERE子句来排除2014-01-20之前任何日期的任何组合。

Answer 1

SELECT   Foo.*
FROM     Foo JOIN Bar ON Bar.foo_id = Foo.id
GROUP BY Foo.id
HAVING   MIN(Bar.ts) >= '2014-01-20'

或者：

SELECT   Foo.*
FROM     Foo JOIN (
           SELECT   foo_id id, MIN(ts) min_ts
           FROM     Bar
           GROUP BY id
         ) t USING (id)
WHERE    t.min_ts >= '2014-01-20'

或者：

SELECT   Foo.*
FROM     Foo JOIN Bar ON Bar.foo_id = Foo.id
GROUP BY Foo.id
HAVING   SUM(Bar.ts >= '2014-01-20')
 AND NOT SUM(Bar.ts <  '2014-01-20')

或者：

SELECT   *
FROM     Foo
WHERE    EXISTS (
           SELECT *
           FROM   Bar
           WHERE  Bar.foo_id = Foo.id
              AND Bar.ts >= '2014-01-20'
         )
 AND NOT EXISTS (
           SELECT *
           FROM   Bar
           WHERE  Bar.foo_id = Foo.id
              AND Bar.ts <  '2014-01-20'
         )

或者：

SELECT   b1.foo_id
FROM     Bar b1 LEFT JOIN Bar b2
      ON b2.foo_id = b1.foo_id
     AND b2.ts <  '2014-01-20'
WHERE    b1.ts >= '2014-01-20'
     AND b2.foo_id IS NULL
GROUP BY b1.foo_id

仅在特定日期之后选择带有条形事件的foo

1 个答案: