上一篇文章介绍了JSON_VALUE，他接受一个JSON输入，输出一个SQL数据类型的标量。
JSON_QUERY也是接受一个JSON输入，但输出的仍是JSON数据类型。
还是通过示例来学习吧。
创建测试表，插入2条数据：
sql
drop table customerTab;
CREATE TABLE
customerTab (custData VARCHAR2(4000),
CONSTRAINT ensure_json2 CHECK (custData IS
JSON STRICT));
CREATE TABLE
customerTab (custData JSON);
INSERT INTO
customerTab
VALUES ('{
"custNo":2,
"name" : "Jane",
"status":"Gold",
"address": {
"Street": "Main Rd 1",
"City": "San Jose",
"zip": 95002
}}');
INSERT INTO
customerTab
VALUES ('{
"custNo":3,
"name" : "Jill",
"status":["Important","Gold"],
"address": {
"Street": "Broadway 2",
"City": "Belmont",
"zip": 94065
}}');
commit;查询地址，返回的是JSON对象：
sql
SQL>
SELECT
JSON_QUERY(custData, '$.address')
FROM
customerTab;
JSON_QUERY(CUSTDATA,'$.ADDRESS')
---------------------------------------------------------------------------------
{"Street":"Main Rd 1","City":"San Jose","zip":95002}
{"Street":"Broadway 2","City":"Belmont","zip":94065}查询状态，返回的第2列是数组，但第一列不是：
sql
SQL>
SELECT
JSON_QUERY(custData, '$.status')
FROM customerTab;
JSON_QUERY(CUSTDATA,'$.STATUS')
-----------------------------------------------------------------------
"Gold"
["Important","Gold"]如果希望都返回数组，可以使用ARRAY WRAPPER子句：
sql
SQL>
SELECT
JSON_QUERY(custData, '$.status' WITH ARRAY WRAPPER)
FROM customerTab;
JSON_QUERY(CUSTDATA,'$.STATUS'WITHARRAYWRAPPER)
-------------------------------------------------------------------
["Gold"]
[["Important","Gold"]]
SQL>
SELECT
JSON_QUERY(custData, '$.status' WITH CONDITIONAL ARRAY WRAPPER)
FROM customerTab;
JSON_QUERY(CUSTDATA,'$.STATUS'WITHCONDITIONALARRAYWRAPPER)
--------------------------------------------------------------------
"Gold"
["Important","Gold"]再插入一条带多个地址的数据：
sql
INSERT INTO
customerTab
VALUES ('{
"custNo":3,
"name" : "Jim",
"status": "Silver",
"address":[
{
"Street": "Fastlane 4",
"City": "Atherton",
"zip": 94027
},
{
"Street": "Slowlane 5",
"City": "San Francisco",
"zip": 94105
} ]
}');
commit;查询地址，可以看出有无ARRAY WRAPPER的区别：
sql
SQL>
SELECT
JSON_QUERY(custData, '$.address[*].City' )
FROM customerTab;
JSON_QUERY(CUSTDATA,'$.ADDRESS[*].CITY')
-----------------------------------------------
"San Jose"
"Belmont"
已选择 3 行。
SQL>
SELECT
JSON_QUERY(custData, '$.address[*].City' WITH ARRAY WRAPPER)
FROM customerTab;
JSON_QUERY(CUSTDATA,'$.ADDRESS[*].CITY'WITHARRAYWRAPPER)
-------------------------------------------------------------------
["San Jose"]
["Belmont"]
["Atherton","San Francisco"]
已选择 3 行。实际上*可以省略，下面SQL等同于上面的SQL：
sql
SELECT
JSON_QUERY(custData, '$.address.City' WITH ARRAY WRAPPER)
FROM customerTab;*表示所有，也可以指定范围：
sql
SELECT
JSON_QUERY(custData, '$.address[0 to 1].City' WITH ARRAY WRAPPER)
FROM customerTab;接下来看官网上的例子。
sql
-- 注意，输入是Lax Syntax，输出则是Strict JSON Syntax
SELECT JSON_QUERY('{a:100, b:200, c:300}', '$') AS value
FROM DUAL;
VALUE
---------------------------------------------------------------------------
{"a":100,"b":200,"c":300}
SELECT JSON_QUERY('{a:100, b:200, c:300}', '$.a' WITH WRAPPER) AS value
FROM DUAL;
VALUE
----------------------------------------------------------------------------
[100]
SELECT JSON_QUERY('{a:100, b:200, c:300}', '$.*' WITH WRAPPER) AS value
FROM DUAL;
VALUE
----------------------------------------------------------------------------
[100,200,300]
SELECT JSON_QUERY('[0,1,2,3,4]', '$') AS value
FROM DUAL;
VALUE
----------------------------------------------------------------------------
[0,1,2,3,4]
SELECT JSON_QUERY('[0,1,2,3,4]', '$' WITH WRAPPER) AS value
FROM DUAL;
VALUE
----------------------------------------------------------------------------
[[0,1,2,3,4]]
SELECT JSON_QUERY('[0,1,2,3,4]', '$[*]' WITH WRAPPER) AS value
FROM DUAL;
VALUE
-----------------------------------------------------------------------------
[0,1,2,3,4]
SELECT JSON_QUERY('[0,1,2,3,4,5,6,7,8]', '$[0, 3 to 5, 7]' WITH WRAPPER) AS value
FROM DUAL;
VALUE
--------------------------------------------------------------------------------
[0,3,4,5,7]
SELECT JSON_QUERY('[{a:100},{b:200},{c:300}]', '$[0]'
WITH CONDITIONAL WRAPPER) AS value
FROM DUAL;
VALUE
--------------------------------------------------------------------------------
{"a":100}
-- 若无WITH CONDITIONAL WRAPPER，则返回null
SELECT JSON_QUERY('[{"a":100},{"b":200},{"c":300}]', '$[*]'
WITH CONDITIONAL WRAPPER) AS value
FROM DUAL;
VALUE
----------------------------------------------------------------------------
[{"a":100},{"b":200},{"c":300}]
-- 和上例类似，只是返回的是SQL数据类型，而非JSON
SELECT JSON_QUERY('[{"a":100},{"b":200},{"c":300}]', '$[*]'
RETURNING VARCHAR2(100) WITH CONDITIONAL WRAPPER) AS value
FROM DUAL;
VALUE
----------------------------------------------------------------------------
[{"a":100},{"b":200},{"c":300}]
-- EMPTY ON ERROR 为默认，其实可以不写。可以改为ERROR ON ERROR试试
SELECT JSON_QUERY('[{"a":100},{"b":200},{"c":300}]', '$[3]'
EMPTY ON ERROR) AS value
FROM DUAL;
VALUE
--------------------------------------------------------------------------------
[]