我有以下psql表。实际上，它有大约20亿行。
id word lemma pos textid country_genre
1 Stuffing stuff vvg 190568 AN
2 her her appge 190568 AN
3 key key nn1 190568 AN
4 into into ii 190568 AN
5 the the at 190568 AN
6 lock lock nn1 190568 AN
7 she she appge 190568 AN
8 pushed push vvd 190568 AN
9 her her appge 190568 AN
10 way way nn1 190568 AN
11 into into ii 190568 AN
12 the the appge 190568 AN
13 house house nn1 190568 AN
14 . . 190568 AN
15 She she appge 190568 AN
16 had have vhd 190568 AN
17 also also rr 190568 AN
18 cajoled cajole vvd 190568 AN
19 her her appge 190568 AN
20 way way nn1 190568 AN
21 into into ii 190568 AN
22 the the at 190568 AN
23 home home nn1 190568 AN
24 . . 190568 AN
.. ... ... .. ... ..
我想创建下表，其中显示所有“方式” - 并排的单词和“country_genre”，“lemma”和“pos”列中的一些数据。
country_genre word word word lemma pos word word word word word lemma pos word word
AN lock she pushed push vvd her way into the house house nn1 . she
AN had also cajoled cajole vvd her way into the home home nn1 . A
AN tried to force force vvi her way into the palace palace nn1 , officials
我使用以下代码（感谢Bohemian：https://stackoverflow.com/a/47496945/3957383！）：
copy(
SELECT
c1.id, c1.country_genre, c1.textid, c1.wordid, c1.word, c2.word, c3.word, c4.word, c4.lemma, c4.pos, c5.word, c6.word, c7.word, c8.word, c9.word, c9.lemma, c9.pos, c10.word, c11.word
FROM
orderedflatcorpus AS c1
JOIN orderedflatcorpus AS c2 ON c1.id + 1 = c2.id
JOIN orderedflatcorpus AS c3 ON c1.id + 2 = c3.id
JOIN orderedflatcorpus AS c4 ON c1.id + 3 = c4.id
JOIN orderedflatcorpus AS c5 ON c1.id + 4 = c5.id
JOIN orderedflatcorpus AS c6 ON c1.id + 5 = c6.id
JOIN orderedflatcorpus AS c7 ON c1.id + 6 = c7.id
JOIN orderedflatcorpus AS c8 ON c1.id + 7 = c8.id
JOIN orderedflatcorpus AS c9 ON c1.id + 8 = c9.id
JOIN orderedflatcorpus AS c10 ON c1.id + 9 = c10.id
JOIN orderedflatcorpus AS c11 ON c1.id + 10 = c11.id
WHERE
c4.pos LIKE 'vv%'
AND c5.pos = 'appge'
AND c6.word = 'way'
AND c7.pos LIKE 'i%'
AND c8.word = 'the'
AND c9.pos LIKE 'n%'
)
TO
'/home/postgres/Results/OUTPUT.csv'
DELIMITER E'\t'
csv header;
此查询返回18706相关结构。
但是，如果我使用以下代码，它提取更多上下文（21而不是11个单词）但在其他方面与前一个相同，则会发生令人担忧的事情：我只得到18555个相关结构。
copy(
SELECT c1.id, c1.country_genre, c1.textid, c1.wordid, c1.word, c1.pos, c2.word, c2.pos, c3.word, c3.pos, c4.word, c4.pos, c5.word, c5.pos, c6.word, c6.pos,
c7.word, c7.pos, c8.word, c8.pos, c8.lemma, c9.word, c9.pos, c10.word, c10.pos, c11.word, c11.pos, c12.word, c12.pos, c13.word, c13.pos, c13.lemma, c14.word,
c14.pos, c15.word, c15.pos, c16.word, c16.pos, c17.word, c17.pos, c18.word, c18.pos, c19.word, c19.pos, c20.word, c20.pos, c21.word, c21.pos
FROM
orderedflatcorpus AS c1
JOIN orderedflatcorpus AS c2 ON c1.id + 1 = c2.id
JOIN orderedflatcorpus AS c3 ON c1.id + 2 = c3.id
JOIN orderedflatcorpus AS c4 ON c1.id + 3 = c4.id
JOIN orderedflatcorpus AS c5 ON c1.id + 4 = c5.id
JOIN orderedflatcorpus AS c6 ON c1.id + 5 = c6.id
JOIN orderedflatcorpus AS c7 ON c1.id + 6 = c7.id
JOIN orderedflatcorpus AS c8 ON c1.id + 7 = c8.id
JOIN orderedflatcorpus AS c9 ON c1.id + 8 = c9.id
JOIN orderedflatcorpus AS c10 ON c1.id + 9 = c10.id
JOIN orderedflatcorpus AS c11 ON c1.id + 10 = c11.id
JOIN orderedflatcorpus AS c12 ON c1.id + 11 = c12.id
JOIN orderedflatcorpus AS c13 ON c1.id + 12 = c13.id
JOIN orderedflatcorpus AS c14 ON c1.id + 13 = c14.id
JOIN orderedflatcorpus AS c15 ON c1.id + 14 = c15.id
JOIN orderedflatcorpus AS c16 ON c1.id + 15 = c16.id
JOIN orderedflatcorpus AS c17 ON c1.id + 16 = c17.id
JOIN orderedflatcorpus AS c18 ON c1.id + 17 = c18.id
JOIN orderedflatcorpus AS c19 ON c1.id + 18 = c19.id
JOIN orderedflatcorpus AS c20 ON c1.id + 19 = c20.id
JOIN orderedflatcorpus AS c21 ON c1.id + 20 = c21.id
WHERE
c8.pos LIKE 'vv%'
AND c9.pos = 'appge'
AND c10.word = 'way'
AND c11.pos LIKE 'i%'
AND c12.word = 'the'
AND c13.pos LIKE 'n%'
)
TO '/home/postgres/Results/OUTPUT.csv' DELIMITER E'\t' csv header;
我查看了第二个查询中缺少的行，但是我无法检测到遗漏的任何模式。
有没有人知道这里会发生什么？谢谢！
在Postgres JOIN相当于INNER JOIN。例如，请参阅this。
换句话说，您的查询需要与所有ON谓词匹配才能得到结果。添加更多JOINS也增加ON谓词无法匹配，从而减少结果的数量。
尝试将JOIN更改为LEFT JOIN（又名LEFT OUTER JOIN）以查看是否可以获得更多结果。
如果没有看到您的示例数据和结果集中缺少的示例，则很难说其他问题可能是什么。
Pirho的答案是正确的 - 就目前而言。但是，仅将连接更改为外连接可能无法解决您的问题。
首先，两个查询的where条件不同，所以我没有理由假设它们将返回相同的结果集。
第二个查询是连续查找21个单词 - 不是19个单词，而不是13个单词。因此，如果模式位于文档的末尾，则无法找到它。
根据你的条件，有13个单词需要连续出现（为你的条件得到计数“13”。然后，我猜，可选7行。这需要内部和外部联接的混合：
FROM orderedflatcorpus c1 JOIN
orderedflatcorpus c2
ON c1.id + 1 = c2.id JOIN
orderedflatcorpus c3
ON c1.id + 2 = c3.id JOIN
orderedflatcorpus c4
ON c1.id + 3 = c4.id JOIN
orderedflatcorpus c5
ON c1.id + 4 = c5.id JOIN
orderedflatcorpus c6
ON c1.id + 5 = c6.id JOIN
orderedflatcorpus c7
ON c1.id + 6 = c7.id JOIN
orderedflatcorpus c8
ON c1.id + 7 = c8.id JOIN
orderedflatcorpus c9
ON c1.id + 8 = c9.id JOIN
orderedflatcorpus c10
ON c1.id + 9 = c10.id JOIN
orderedflatcorpus c11
ON c1.id + 10 = c11.id JOIN
orderedflatcorpus c12
ON c1.id + 11 = c12.id JOIN
orderedflatcorpus c13
ON c1.id + 12 = c13.id
orderedflatcorpus c14
ON c1.id + 13 = c14.id LEFT JOIN
orderedflatcorpus c15
ON c1.id + 14 = c15.id LEFT JOIN
orderedflatcorpus c16
ON c1.id + 15 = c16.id LEFT JOIN
orderedflatcorpus c17
ON c1.id + 16 = c17.id LEFT JOIN
orderedflatcorpus c18
ON c1.id + 17 = c18.id LEFT JOIN
orderedflatcorpus c19
ON c1.id + 18 = c19.id LEFT JOIN
orderedflatcorpus c20
ON c1.id + 19 = c20.id LEFT JOIN
orderedflatcorpus c21
ON c1.id + 20 = c21.id
WHERE c8.pos LIKE 'vv%' AND
c9.pos = 'appge' AND
c10.word = 'way' AND
c11.pos LIKE 'i%' AND
c12.word = 'the' AND
c13.pos LIKE 'n%' ;
下一篇：我怀疑country和/或textid应该是join条件的一部分。