建表：
create table jtest01(
id int,
jdoc json
);
----------------------------------------------------------------------------------
create or replace function random_string(INTEGER)
RETURNS TEXT AS
$BODY$
select array_to_string(
	array(
		select substring(
			'0123456789ABCDEFGHIGKLMNOPQRSTUVWXYZabcdefghijgklmnopqrstuvwxyz' 
			from (ceil(random()*62))::int FOR 1
		)
		from generate_series(1,$1)


	),''
)


$BODY$
LANGUAGE sql VOLATILE;


------------------------------------------------------------------------------------------
插入測試資料：
insert into  jtest01 
select t.seq,('{"a":{"a1":"a1a1","a2":"a2a2"},
		"name":"'|| random_string(10) || '", 
		"b":"bbbbbbbb"}')::json 
from generate_series(1,100000) as t(seq);


select * from jtest01 limit 30000;
-----------------------------------------------------------------------------------------
建函式索引：
create index on jtest01 USING btree (json_extract_path_text(jdoc,'name'));
-----------------------------------------------------------------------------------------
ANALYZE jtest01;
-----------------------------------------------------------------------------------------
沒有走函式索引的執行計劃：
explain ANALYZE VERBOSE select * from jtest01 where jdoc->>'name'='lnBtcJLR85';


testdb2=# explain ANALYZE VERBOSE select * from jtest01 where jdoc->>'name'='lnBtcJLR85';
                                                   QUERY PLAN                                                   
----------------------------------------------------------------------------------------------------------------
 Seq Scan on public.jtest01  (cost=0.00..2834.00 rows=500 width=80) (actual time=94.029..94.029 rows=0 loops=1)
   Output: id, jdoc
   Filter: ((jtest01.jdoc ->> 'name'::text) = 'lnBtcJLR85'::text)
   Rows Removed by Filter: 100000
 Planning time: 0.297 ms
 Execution time: 94.052 ms
(6 rows)
-------------------------------------------------------------------------------------------------------------
走了函式索引的執行計劃：
explain ANALYZE VERBOSE select * from jtest01 where json_extract_path_text( jdoc,'name')='lnBtcJLR85';


testdb2=# explain ANALYZE VERBOSE select * from jtest01 where json_extract_path_text( jdoc,'name')='lnBtcJLR85';
                                                                     QUERY PLAN                                                         
            
-----------------------------------------------------------------------------------------------------------------
 Index Scan using jtest01_json_extract_path_text_idx on public.jtest01  (cost=0.42..8.44 rows=1 width=80) (actual time=0.047..0.047 rows
=0 loops=1)
   Output: id, jdoc
   Index Cond: (json_extract_path_text(jtest01.jdoc, VARIADIC '{name}'::text[]) = 'lnBtcJLR85'::text)
 Planning time: 0.307 ms
 Execution time: 0.088 ms
(5 rows)
---------------------------------------------------------------------------------------------------------------




再看看在JSONB型別上建索引的例子
建測試表：
create table jtest02(
id int,
jdoc jsonb
);


create table jtest03(
id int,
jdoc jsonb
);


---------------------------------------------------------------------------------------
插入測試資料
insert into jtest02 select id,jdoc::jsonb from jtest01;
insert into jtest03 select * from jtest02;


--------------------------------------------------------------------------------------
建gin索引
create index idx_jtest02_jdoc on jtest02 USING gin (jdoc);
create index idx_jtest03_jdoc on jtest03 USING gin (jdoc jsonb_path_ops);


------------------------------------------------------------------------------------
對錶進行分析：
analyze jtest02;
analyze jtest03;


select * from jtest02 where jdoc @> '{"name":"sHWIXgOREa"}';
select * from jtest03 where jdoc @> '{"name":"sHWIXgOREa"}';


---------------------------------------------------------------------------------------
檢視執行計劃：
explain analyze verbose select * from jtest02 where jdoc @> '{"name":"sHWIXgOREa"}';


"Bitmap Heap Scan on public.jtest02  (cost=28.77..344.97 rows=100 width=91) (actual time=0.066..0.066 rows=1 loops=1)"
"  Output: id, jdoc"
"  Recheck Cond: (jtest02.jdoc @> '{"name": "sHWIXgOREa"}'::jsonb)"
"  Heap Blocks: exact=1"
"  ->  Bitmap Index Scan on idx_jtest02_jdoc  (cost=0.00..28.75 rows=100 width=0) (actual time=0.059..0.059 rows=1 loops=1)"
"        Index Cond: (jtest02.jdoc @> '{"name": "sHWIXgOREa"}'::jsonb)"
"Planning time: 0.048 ms"
"Execution time: 0.083 ms"


explain analyze verbose select * from jtest03 where jdoc @> '{"name":"sHWIXgOREa"}';


"Bitmap Heap Scan on public.jtest03  (cost=16.77..332.97 rows=100 width=91) (actual time=0.018..0.019 rows=1 loops=1)"
"  Output: id, jdoc"
"  Recheck Cond: (jtest03.jdoc @> '{"name": "sHWIXgOREa"}'::jsonb)"
"  Heap Blocks: exact=1"
"  ->  Bitmap Index Scan on idx_jtest03_jdoc  (cost=0.00..16.75 rows=100 width=0) (actual time=0.009..0.009 rows=1 loops=1)"
"        Index Cond: (jtest03.jdoc @> '{"name": "sHWIXgOREa"}'::jsonb)"
"Planning time: 0.052 ms"
"Execution time: 0.036 ms"
------------------------------------------------------------------------------------------------------------------------
檢視索引的大小
select pg_indexes_size('jtest02');
testdb2=# select pg_indexes_size('jtest02');
 pg_indexes_size 
-----------------
         8224768
(1 row)


select pg_indexes_size('jtest03');
testdb2=# select pg_indexes_size('jtest03');
 pg_indexes_size 
-----------------
         5980160
(1 row)
可看出jsonb_path_ops型別的索引要比jsonb_ops的小。