我在Postgres中有一个TEXT indexPath.row列：
keyvalues我的查询必须从比赛中间排除select * from test5 limit 5;
id | keyvalues
----+------------------------------------------------------
1 | ^ first 1 | second 3
2 | ^ first 1 | second 2 ^ first 2 | second 3
3 | ^ first 1 | second 2 | second 3
4 | ^ first 2 | second 3 ^ first 1 | second 2 | second 2
5 | ^ first 2 | second 3 ^ first 1 | second 3
字符，因此我使用的是正则表达式：
^查询有效（零行匹配），但是在7秒以上的速度太慢了。
我认为使用三字母组合索引会有所帮助，但没有运气：
explain analyze select count(*) from test5 where keyvalues ~* '\^ first 1[^\^]+second 0';
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------
Finalize Aggregate (cost=78383.31..78383.32 rows=1 width=8) (actual time=7332.030..7332.030 rows=1 loops=1)
-> Gather (cost=78383.10..78383.30 rows=2 width=8) (actual time=7332.021..7337.138 rows=3 loops=1)
Workers Planned: 2
Workers Launched: 2
-> Partial Aggregate (cost=77383.10..77383.10 rows=1 width=8) (actual time=7328.155..7328.156 rows=1 loops=3)
-> Parallel Seq Scan on test5 (cost=0.00..77382.50 rows=238 width=0) (actual time=7328.146..7328.146 rows=0 loops=3)
Filter: (keyvalues ~* '\^ first 1[^\^]+second 0'::text)
Rows Removed by Filter: 1666668
Planning Time: 0.068 ms
Execution Time: 7337.184 ms
带有三字母组合索引的查询要慢 3倍！它仍然返回正确的结果（零行）。我希望trigram索引能够立即发现任何地方都没有create extension if not exists pg_trgm;
create index on test5 using gin (keyvalues gin_trgm_ops);
explain analyze select count(*) from test5 where keyvalues ~* '\^ first 1[^\^]+second 0';
QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=1484.02..1484.03 rows=1 width=8) (actual time=23734.646..23734.646 rows=1 loops=1)
-> Bitmap Heap Scan on test5 (cost=1480.00..1484.01 rows=1 width=0) (actual time=23734.641..23734.641 rows=0 loops=1)
Recheck Cond: (keyvalues ~* '\^ first 1[^\^]+second 0'::text)
Rows Removed by Index Recheck: 5000005
Heap Blocks: exact=47620
-> Bitmap Index Scan on test5_keyvalues_idx (cost=0.00..1480.00 rows=1 width=0) (actual time=1756.158..1756.158 rows=5000005 loops=1)
Index Cond: (keyvalues ~* '\^ first 1[^\^]+second 0'::text)
Planning Time: 0.412 ms
Execution Time: 23734.722 ms
字符串，而且速度很快。
（动机：我想避免将second 0标准化为another table，所以我希望使用文本索引和在单个keyvalues字段中编码匹配逻辑逻辑运算符有效，但是太慢了，as is JSONB。）
答案 0 :(得分：2)
如您所见，这对于三字组不能很好地工作。 Trigram在空间边界上不匹配，因此，如果您的所有数据都包含相同的单词，则索引将匹配每一行。
这可能使事情更清楚：
with data as (select * from (values ('^ first 1 | second 3'),
('^ first 1 | second 2 ^ first 2 | second 3'),
('^ first 1 | second 2 | second 3'),
('^ first 2 | second 3 ^ first 1 | second 2 | second 2'),
('^ first 2 | second 3 ^ first 1 | second 3')
) v(keyvalues)
)
select keyvalues, show_trgm(keyvalues) from data;
keyvalues | show_trgm
------------------------------------------------------+-------------------------------------------------------------------------------------------------------
^ first 1 | second 3 | {" 1"," 3"," f"," s"," 1 "," 3 "," fi"," se",con,eco,fir,irs,"nd ",ond,rst,sec,"st "}
^ first 1 | second 2 ^ first 2 | second 3 | {" 1"," 2"," 3"," f"," s"," 1 "," 2 "," 3 "," fi"," se",con,eco,fir,irs,"nd ",ond,rst,sec,"st "}
^ first 1 | second 2 | second 3 | {" 1"," 2"," 3"," f"," s"," 1 "," 2 "," 3 "," fi"," se",con,eco,fir,irs,"nd ",ond,rst,sec,"st "}
^ first 2 | second 3 ^ first 1 | second 2 | second 2 | {" 1"," 2"," 3"," f"," s"," 1 "," 2 "," 3 "," fi"," se",con,eco,fir,irs,"nd ",ond,rst,sec,"st "}
^ first 2 | second 3 ^ first 1 | second 3 | {" 1"," 2"," 3"," f"," s"," 1 "," 2 "," 3 "," fi"," se",con,eco,fir,irs,"nd ",ond,rst,sec,"st "}
您可以使用部分索引来排除中间带有^的行吗？
答案 1 :(得分：1)
根据OP，用户@jjanes在DBA.SE上给出了正确的答案here：
我希望trigram索引能够立即找出在任何地方都没有
* Note: Using again the example "foo bar", we will not consider the * trigram " b", though this trigram would be found by the trigram * extraction code. Since we will find " ba", it doesn't seem worth * trying to hack the algorithm to generate the additional trigram.字符串的情况“第二”和“ 0”是单独的词，因此它无法检测到它们的联合缺失。似乎可以检测到'0'的缺失，但是来自“ contrib / pg_trgm / trgm_regexp.c”的注释似乎很相关：
{{1}}由于模式字符串中的最后一个字符为0，因此也不会有形式为“ 0a”的三字母组合，因此就错过了这个机会。
即使不是出于此限制，您的方法似乎也非常脆弱。