10.数据类型-json/jsonb类型
文章目录
- 前言
- 一、json/jsonb类型
-
- 1.json类型简介
- 2.查询json数据
- 3.jsonb与json差异
- 4.jsonb与json操作符
- 5.jsonb与json函数
- 6.jsonb键/值的追加、删除、更新
前言
一、json/jsonb类型
PostgreSQL不只是一个关系型数据库，同时它还支持非关系数据类型json,
json属于重量级的非常规数据类型。
1.json类型简介
select '{"a":1,"b":2}'::json;
[email protected]:5432=>select '{"a":1,"b":2}'::json;
json
---------------
{"a":1,"b":2}
(1 row)
演示json类型，接下来创建一张表test_json1:
create table lhc.test_json1(id serial primary key,name json);
插入表数据:
insert into test_json1 (name)
values ('{"col1":1,"col2":"lian","col3":"hui"}');
[email protected]:5432=>insert into test_json1 (name)
values ('{"col1":1,"col2":"lian","col3":"hui"}');lhcdb->
INSERT 0 1
insert into test_json1 (name)
values ('{"col1":2,"col2":"LIAN","col3":"JIA"}');
[email protected]:5432=>insert into test_json1 (name)
values ('{"col1":2,"col2":"LIAN","col3":"JIA"}');lhcdb->
INSERT 0 1
查询表test_json1:
select * from test_json1;
[email protected]:5432=>select * from test_json1;
id | name
----+---------------------------------------
1 | {"col1":1,"col2":"lian","col3":"hui"}
2 | {"col1":2,"col2":"LIAN","col3":"JIA"}
(2 rows)
2.查询json数据
通过"->"操作符可以查询json数据的键值:
select name -> 'col2' from test_json1 where id=1;
[email protected]:5432=>select name -> 'col2' from test_json1 where id=1;
?column?
----------
"lian"
(1 row)
使用->>操作符，以文本格式返回json字段键值:
select name ->> 'col2' from test_json1 where id = 1;
[email protected]:5432=>select name ->> 'col2' from test_json1 where id = 1;
?column?
----------
lian
(1 row)
3.jsonb与json差异
两者区别以下:
json存储格式为文本；而jsonb存储格式为二进制。
存储格式不同，使得两种json数据类型的处理效率不一样。
json类型:以文本存储并且存储的内容和输入数据一样，当检索json数据时必须重新解析。
jsonb类型:以二进制形式存储已解析好的数据，当检索jsonb数据时不需要重新解析。
因此结论:
json写入比jsonb快，但检索比jsonb慢。
json和jsonb在使用过程中还存在差异:
jsonb输出的键的顺序和输入不一样:
select '{"bar":"baz","balance":7.77,"active":false}'::jsonb;
[email protected]:5432=>select '{"bar":"baz","balance":7.77,"active":false}'::jsonb;
jsonb
--------------------------------------------------
{"bar": "baz", "active": false, "balance": 7.77}
(1 row)
而json输出的键的顺序和输入完全一样:
select '{"bar":"baz","balance":7.77,"active":false}'::json;
[email protected]:5432=>select '{"bar":"baz","balance":7.77,"active":false}'::json;
json
---------------------------------------------
{"bar":"baz","balance":7.77,"active":false}
(1 row)
jsonb类型会去掉输入数据中键值的空格:
select '{"id":1, "name":"francs"}'::jsonb;
[email protected]:5432=>select '{"id":1, "name":"francs"}'::jsonb;
jsonb
-----------------------------
{"id": 1, "name": "francs"}
(1 row)
json类型不会去掉输入数据中键值的空格:
select '{"id":1, "name":"francs"}'::json;
[email protected]:5432=>select '{"id":1, "name":"francs"}'::json;
json
------------------------------
{"id":1, "name":"francs"}
(1 row)
jsonb会删除重复的键，仅保留最后一个:
select '{"id":1,"name":"francs","remark":"a good guy!","name":"test"}'::jsonb;
[email protected]:5432=>select '{"id":1,"name":"francs","remark":"a good guy!","name":"test"}'::jsonb;
jsonb
----------------------------------------------------
{"id": 1, "name": "test", "remark": "a good guy!"}
(1 row)
json数据类型会保留重复的键值:
select '{"id":1,"name":"francs","remark":"a good guy!","name":"test"}'::json;
[email protected]:5432=>select '{"id":1,"name":"francs","remark":"a good guy!","name":"test"}'::json;
json
---------------------------------------------------------------
{"id":1,"name":"francs","remark":"a good guy!","name":"test"}
(1 row)
4.jsonb与json操作符
以文本格式返回json类型的字段键值可以使用"->>"操作符:
select name ->> 'col2' from test_json1 where id = 1;
[email protected]:5432=>select name ->> 'col2' from test_json1 where id = 1;
?column?
----------
lian
(1 row)
字符串是否作为顶层键值:
select '{"a":1,"b":2}'::jsonb ? 'a';
[email protected]:5432=>select '{"a":1,"b":2}'::jsonb ? 'a';
?column?
----------
t
(1 row)
删除json数据的键/值:
select '{"a":1,"b":2}'::jsonb - 'a';
[email protected]:5432=>select '{"a":1,"b":2}'::jsonb - 'a';
?column?
----------
{"b": 2}
(1 row)
5.jsonb与json函数
扩展最外层的json对象成为一组键/值结果集:
select * from json_each('{"a":"lian","b":"hui"}');
[email protected]:5432=>select * from json_each('{"a":"lian","b":"hui"}');
key | value
-----+--------
a | "lian"
b | "hui"
(2 rows)
以文本形式返回结果:
select * from json_each_text('{"a":"foo","b":"bar"}');
[email protected]:5432=>select * from json_each_text('{"a":"foo","b":"bar"}');
key | value
-----+-------
a | foo
b | bar
(2 rows)
将一个普通表转换成json类型的表:
select * from lhc.test_area where id = 1;
[email protected]:5432=>select * from lhc.test_area where id = 1;
id | name | fatherid
----+------+----------
1 | 中国 | 0
(1 row)
select row_to_json(test_area) from lhc.test_area where id = 1;
[email protected]:5432=>select row_to_json(test_area) from lhc.test_area where id = 1;
row_to_json
-------------------------------------
{"id":1,"name":"中国","fatherid":0}
(1 row)
返回最外层的json对象中的键的集合:
select * from json_object_keys('{"a":"foo","b":"bar"}');
[email protected]:5432=>select * from json_object_keys('{"a":"foo","b":"bar"}');
json_object_keys
------------------
a
b
(2 rows)
6.jsonb键/值的追加、删除、更新
jsonb键/值追加可通过"||"操作符:
select '{"name":"francs","age":"31"}'::jsonb||'{"sex":"male"}'::jsonb;
[email protected]:5432=>select '{"name":"francs","age":"31"}'::jsonb||'{"sex":"male"}'::jsonb;
?column?
------------------------------------------------
{"age": "31", "sex": "male", "name": "francs"}
(1 row)
jsonb键/值的删除有两种方法:
一种是通过操作符"-"删除:
select '{"name":"James","email":"[email protected]"}'::jsonb - 'email';
[email protected]:5432=>select '{"name":"James","email":"[email protected]"}'::jsonb - 'email';
?column?
-------------------
{"name": "James"}
(1 row)
select '["red","green","blue"]'::jsonb - 0;
[email protected]:5432=>select '["red","green","blue"]'::jsonb - 0;
?column?
-------------------
["green", "blue"]
(1 row)
另一种通过操作符"#-"删除指定键/值:
删除嵌套aliases中的位置为1的键值:
select '{"name":"James","aliases":["James","The Jamester","J Man"]}'::jsonb #- '{aliases,1}'::text[];
[email protected]:5432=>select '{"name":"James","aliases":["James","The Jamester","J Man"]}'::jsonb #- '{aliases,1}'::text[];
?column?
--------------------------------------------------
{"name": "James", "aliases": ["James", "J Man"]}
(1 row)
删除嵌套contact中的fax键值:
select '{"name":"James","contact":{"phone":"01234 567890","fax":"01987 543210"}}'::jsonb #- '{contact,fax}'::text[];
[email protected]:5432=>select '{"name":"James","contact":{"phone":"01234 567890","fax":"01987 543210"}}'::jsonb #- '{contact,fax}'::text[];
?column?
---------------------------------------------------------
{"name": "James", "contact": {"phone": "01234 567890"}}
(1 row)
jsonb键/值的更新也有两种方法:
第一种方式为"||"操作符，"||"操作符可以连接json键，也可以覆盖重复的键值。
修改age键的值:
select '{"name":"francs","age":"31"}'::jsonb || '{"age":"32"}'::jsonb;
[email protected]:5432=>select '{"name":"francs","age":"31"}'::jsonb || '{"age":"32"}'::jsonb;
?column?
---------------------------------
{"age": "32", "name": "francs"}
(1 row)
第二种方式是通过jsonb_set函数:
jsonb_set(target jsonb,path text[],new_value jsonb[,create_missing boolean]);
target指源jsonb數據，path指路徑，new_value指更新後的鍵值，
create_missing值為true表示如果键不存在则添加，
create_missing值為false表示如果键不存在则不添加。
select jsonb_set('{"name":"francs","age":"31"}'::jsonb,'{age}','"32"'::jsonb,false);
[email protected]:5432=>select jsonb_set('{"name":"francs","age":"31"}'::jsonb,'{age}','"32"'::jsonb,false);
jsonb_set
---------------------------------
{"age": "32", "name": "francs"}
(1 row)
select jsonb_set('{"name":"francs","age":"31"}'::jsonb,'{sex}','"male"'::jsonb,true);
[email protected]:5432=>select jsonb_set('{"name":"francs","age":"31"}'::jsonb,'{sex}','"male"'::jsonb,true);
jsonb_set
------------------------------------------------
{"age": "31", "sex": "male", "name": "francs"}
(1 row)