标签

PostgreSQL , json , 索引 , gin , btree_gin , 范围检索 , 表达式索引

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背景

JSON，JSONB是PG从9就开始引入的数据类型，开发人员非常喜欢，对于JSON里面的内容的检索，我们可以使用GIN索引，目前直接对JSON字段创建GIN索引，可以支持任意PATH的等值、包含检索。

https://www.postgresql.org/docs/10/static/datatype-json.html#JSON-INDEXING

但是，在多数场景中，我们可能还需要范围检索的需求，例如消费范围，年龄范围，收入范围等等。

使用表达式组合索引，很好的满足需求。

例子

单KEY，直接用btree索引

postgres=# create table test (id int, js jsonb);  
CREATE TABLE  

postgres=# create index idx_test_2 on test using btree (((js->>'key1')::int));  
CREATE INDEX  

postgres=# explain select * from test where (js->>'key1')::int between 1 and 10 ;  
                                              QUERY PLAN                                                
------------------------------------------------------------------------------------------------------  
 Index Scan using idx_test_2 on test  (cost=0.15..24.27 rows=6 width=36)  
   Index Cond: ((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10))  
(2 rows)  

多KEY混合，使用btree_gin, 表达式索引

例如需要查询key1,key2,key3的任意组合范围查询。

postgres=# create extension btree_gin;  
CREATE EXTENSION  

postgres=# create index idx_test_1 on test using gin (((js->>'key1')::int), ((js->>'key2')::int), ((js->>'key3')::int));  
CREATE INDEX  

postgres=# explain select * from test where (js->>'key1')::int between 1 and 10   
postgres-# ;  
                                                 QUERY PLAN                                                   
------------------------------------------------------------------------------------------------------------  
 Bitmap Heap Scan on test  (cost=24.07..33.64 rows=6 width=36)  
   Recheck Cond: ((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10))  
   ->  Bitmap Index Scan on idx_test_1  (cost=0.00..24.06 rows=6 width=0)  
         Index Cond: ((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10))  
(4 rows)  

postgres=# explain select * from test where (js->>'key1')::int between 1 and 10  or (js->>'key2')::int between 1 and 15;  
                                                                                             QUERY PLAN                                                                                               
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  
 Bitmap Heap Scan on test  (cost=48.13..59.32 rows=13 width=36)  
   Recheck Cond: (((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10)) OR ((((js ->> 'key2'::text))::integer >= 1) AND (((js ->> 'key2'::text))::integer <= 15)))  
   ->  BitmapOr  (cost=48.13..48.13 rows=13 width=0)  
         ->  Bitmap Index Scan on idx_test_1  (cost=0.00..24.06 rows=6 width=0)  
               Index Cond: ((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10))  
         ->  Bitmap Index Scan on idx_test_1  (cost=0.00..24.06 rows=6 width=0)  
               Index Cond: ((((js ->> 'key2'::text))::integer >= 1) AND (((js ->> 'key2'::text))::integer <= 15))  
(7 rows)  

postgres=# explain select * from test where (js->>'key1')::int between 1 and 10  and (js->>'key2')::int between 1 and 15;  
                                                                                             QUERY PLAN                                                                                                
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------  
 Bitmap Heap Scan on test  (cost=40.00..44.05 rows=1 width=36)  
   Recheck Cond: ((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10) AND (((js ->> 'key2'::text))::integer >= 1) AND (((js ->> 'key2'::text))::integer <= 15))  
   ->  Bitmap Index Scan on idx_test_1  (cost=0.00..40.00 rows=1 width=0)  
         Index Cond: ((((js ->> 'key1'::text))::integer >= 1) AND (((js ->> 'key1'::text))::integer <= 10) AND (((js ->> 'key2'::text))::integer >= 1) AND (((js ->> 'key2'::text))::integer <= 15))  
(4 rows)  

参考

https://www.postgresql.org/docs/10/static/datatype-json.html#JSON-INDEXING

https://www.postgresql.org/docs/10/static/btree-gin.html