可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试):
问题:
I have the following constructor (as a test):
CREATE TABLE product (id BIGSERIAL PRIMARY KEY, ext hstore); CREATE INDEX ix_product_ext ON product USING GIN(ext); INSERT INTO product (id, ext) SELECT id, ('size=>' || CEILING(10 + RANDOM() * 90) || ',mass=>' || CEILING(10 + RANDOM() * 90))::hstore FROM generate_series(1, 100000) id;
I have the following query, which works ok:
SELECT COUNT(id) FROM ( SELECT id FROM product WHERE (ext->'size')::INT >= 41 AND (ext->'mass')::INT <= 20 ) T
But I believe the correct way to do this is using the @> operator. I have the following, but it gives a syntax error:
SELECT COUNT(id) FROM ( SELECT id FROM product WHERE ext @> 'size>=41,mass<=20' ) T
How should I write this?
回答1:
Reading hstore documentation your (last query) size>=41 does not mean "when size is greater or equal than 41":
text => text make single-pair hstore
Following that you can't write mass<=20, because there is no such operation. Using @> operator:
hstore @> hstore does left operand contain right?
you can write:
SELECT count(id) FROM product WHERE ext @> 'size=>41,mass=>20';
However it takes only these products where size is equal to 41 and mass is equal to 20.
回答2:
Your initial attempt is correct but you need to use (partial) btree indexes and bitmap index scans to rely on it:
create index on product(((ext->'size')::int)) where ((ext->'size') is not null);
The same for mass, and if the planner doesn't get it on the spot add two where clauses, ie where ext->'size' is not null and the same for mass.
If there is a pattern of some kind (which is likely, since most products with a size also have a mass), potentially create a multicolumn index combining the two - one sac, the other desc.
The gin index as you wrote it, along with the accompanying query (with a syntax error) will basically do the same thing but unordered; it'll be slower.
