Question

我有一个我想简化的查询：

select
      sequence,
      1 added
      from scoredtable
      where score_timestamp=1292239056000
      and sequence
      not in (select sequence from scoredtable where score_timestamp=1292238452000)
      union
select
      sequence,
      0 added
      from scoredtable
      where score_timestamp=1292238452000
      and sequence
      not in (select sequence from scoredtable where score_timestamp=1292239056000);

有什么想法吗？基本上我想从同一个表中提取两个时间戳值之间不同的所有序列。使用colum“added”表示行是否为新行或是否已删除行。

来源表：

score_timestamp             sequence
1292239056000               0
1292239056000               1
1292239056000               2
1292238452000               1
1292238452000               2
1292238452000               3

之间的示例（1292239056000,1292238452000）查询结果（2行）：

sequence added
3        1
0        0

之间的示例（1292238452000,1292239056000）查询结果（2行）：

sequence added
0        1
3        0

之间的示例（1292239056000,1292239056000）查询结果（0行）：

sequence added

Answer 1

此查询获取在两个时间戳中仅出现一次的所有sequences，并检查它是否出现在第一个时间戳或第二个时间戳中。

SELECT
  sequence,
  CASE WHEN MIN(score_timestamp) = 1292239056000 THEN 0 ELSE 1 END AS added
FROM scoredtable
WHERE score_timestamp IN ( 1292239056000, 1292238452000 )
  AND ( 1292239056000 <> 1292238452000 )   -- No rows, when timestamp is the same
GROUP BY sequence
HAVING COUNT(*) = 1

它会返回您想要的结果：

sequence added
3       1
0       0

Answer 2

给出两个时间戳

SET @ts1 := 1292239056000
SET @ts2 := 1292238452000

您可以通过以下方式获取和删除

SELECT s1.sequence AS sequence, 0 as added
FROM scoredtable s1 LEFT JOIN
     scoredtable s2 ON 
                       s2.score_timestamp = @ts2 AND
                       s1.sequence = s2.sequence
WHERE
     s1.score_timestamp = @ts1 AND
     s2.score_timestampe IS NULL
UNION ALL
SELECT s2.sequence, 1
FROM scoredtable s1 RIGHT JOIN
     scoredtable s2 ON s1.score_timestamp = @ts1 AND
                       s1.sequence = s2.sequence
WHERE
     s2.score_timestamp = @ts2 AND
     s1.score_timestampe IS NULL

取决于行数和统计数据，上面的查询可能会执行得更好然后分组并且有count（*）= 1版本（我认为总是需要全表扫描，而上面的联合应该能够做到2 x anti-join，可能会更好）

如果您有大量数据集，请告诉我们哪个更快（使用SQL_NO_CACHE进行测试以获得可比较的结果）

MySQL - 如何简化此查询？

2 个答案: