Question

我有一个包含文字文件中的字词的大表格（offset_1只是offset - 1）：

file  offset offset_1 word
----  ------ -------- ----
1.txt   1       0     I
1.txt   2       1     have
1.txt   3       2     a
1.txt   4       3     large
1.txt   5       4     table
1.txt   6       5     that
1.txt   7       6     contains

我希望在给定距离或更短的距离内找到成对的单词。例如，＆＃34; a＆＃34;和＆＃34;表＆＃34;中间至多有1个字。

我现在所做的是（在MySQL中）：

SELECT t1.offset, t3.offset
FROM t as t1 JOIN t as t2 JOIN t as t3
ON t2.file = t1.file AND t3.file = t1.file AND 
(
     (t1.offset = t2.offset_1 AND t2.offset = t3.offset_1) # "a large table"
  OR (t1.offset = t3.offset_1 AND t2.offset = 1)           # "a table"
)
WHERE t1.word = 'a' AND t3.word = 'table'

但这永远不会终止（表格很大）。

如果我删除了OR中的两个条件中的任何一个，它就能正常找到＆＃34;一个大表＆＃34;或者＆＃34;表格＆＃34;分别。

正确的方法是什么？

Answer 1

这会有效吗

SELECT t1.offset, t2.offset
FROM t as t1 
JOIN t as t2 ON t2.file = t1.file 
WHERE t1.word = 'a' AND t2.word = 'table'
AND (t2.offset - t1.offset) <= 2

Answer 2

我建议使用union all将其拆分为两个查询。这样的事情：

SELECT t1.offset, t3.offset
FROM t t1 JOIN
     t t2
     ON t2.file = t1.file AND t1.offset = t2.offset_1
WHERE t1.word = 'a' AND t2.word = 'table'
UNION ALL
SELECT t1.offset, t3.offset
FROM t t1 JOIN
     t t2
     ON t2.file = t1.file AND t1.offset = t2.offset_1 JOIN
     t t3
     ON t3.file = t2.file and t2.offset = t3.offset_1
WHERE t1.word = 'a' AND t3.word = 'table';

OR条件下的{p> JOIN通常会对效果产生不良影响。有时将逻辑分成多个子查询可能是一个很大的胜利

MySQL：链中的推理

2 个答案: