Oracle 中的 JSON_OBJECT 增强功能

本文讲述Oracle Database 19c 中的 JSON_OBJECT 函数的增强功能。

1、初始化

本文中的示例使用SCOTT模式中的DEPT表，如下：

-- DROP TABLE DEPT PURGE;

CREATE TABLE DEPT (
  DEPTNO NUMBER(2) CONSTRAINT PK_DEPT PRIMARY KEY,
  DNAME VARCHAR2(14),
  LOC VARCHAR2(13)
);

INSERT INTO DEPT VALUES (10,'ACCOUNTING','NEW YORK');
INSERT INTO DEPT VALUES (20,'RESEARCH','DALLAS');
INSERT INTO DEPT VALUES (30,'SALES','CHICAGO');
INSERT INTO DEPT VALUES (40,'OPERATIONS','BOSTON');
COMMIT;

2、通配符

通配符“*”可用作 JSON_OBJECT 函数的输入，以在单个步骤中引用所有列。使用列名作为键，将每列转换为键：key:value。

SELECT JSON_OBJECT(*) AS json_data
FROM   dept;

JSON_DATA
-------------------------------------------------------
{"DEPTNO":10,"DNAME":"ACCOUNTING","LOC":"NEW YORK"}
{"DEPTNO":20,"DNAME":"RESEARCH","LOC":"DALLAS"}
{"DEPTNO":30,"DNAME":"SALES","LOC":"CHICAGO"}
{"DEPTNO":40,"DNAME":"OPERATIONS","LOC":"BOSTON"}

SQL>

通配符也可以是表或视图别名的前缀。

SELECT JSON_OBJECT(a.*) AS json_data
FROM   dept a;

JSON_DATA
-------------------------------------------------------
{"DEPTNO":10,"DNAME":"ACCOUNTING","LOC":"NEW YORK"}
{"DEPTNO":20,"DNAME":"RESEARCH","LOC":"DALLAS"}
{"DEPTNO":30,"DNAME":"SALES","LOC":"CHICAGO"}
{"DEPTNO":40,"DNAME":"OPERATIONS","LOC":"BOSTON"}

SQL>

3、列列表

可以将逗号分隔的列列表指定为 JSON_OBJECT 函数的输入。在查询中使用的情况下，键名与列表中的列名匹配。以下查询使用小写的列名称，因此输出的键字是小写的。

SELECT JSON_OBJECT(deptno, dname) AS json_data
FROM   dept;

JSON_DATA
-------------------------------------------------------
{"deptno":10,"dname":"ACCOUNTING"}
{"deptno":20,"dname":"RESEARCH"}
{"deptno":30,"dname":"SALES"}
{"deptno":40,"dname":"OPERATIONS"}

SQL>

在以下示例中，列名称是首字段大写，因此键名称在输出中也是首字母大写。

SELECT JSON_OBJECT(Deptno, Dname) AS json_data
FROM   dept;

JSON_DATA
-------------------------------------------------------
{"Deptno":10,"Dname":"ACCOUNTING"}
{"Deptno":20,"Dname":"RESEARCH"}
{"Deptno":30,"Dname":"SALES"}
{"Deptno":40,"Dname":"OPERATIONS"}

SQL>

4、键值（Key-Value）定义

在以前的版本中，键值对以两种方式之一定义，使用KEY和VALUE关键字，或省略KEY关键字，以下所示：

SELECT JSON_OBJECT(KEY 'deptno' VALUE deptno,
                   KEY 'dname' VALUE dname) AS json_data
FROM   dept;


SELECT JSON_OBJECT('deptno' VALUE deptno,
                   'dname' VALUE dname) AS json_data
FROM   dept;

在Oracle 19c中，有一个更短的选项，用“:”代替VALUE关键字。

SELECT JSON_OBJECT('deptno' : deptno,
                   'dname' : dname) AS json_data
FROM   dept;

JSON_DATA
-------------------------------------------------------
{"deptno":10,"dname":"ACCOUNTING"}
{"deptno":20,"dname":"RESEARCH"}
{"deptno":30,"dname":"SALES"}
{"deptno":40,"dname":"OPERATIONS"}

SQL>

5、列别名

您不能在 JSON_OBJECT 函数调用本身中对列进行别名，也不需要这样做，但可以在 WITH 子句或内联视图中进行别名。

WITH converted_data AS (
  SELECT deptno AS "deptnoCol",
         dname AS "dnameCol"
  FROM   dept
)
SELECT JSON_OBJECT(a.*) AS json_data
FROM   converted_data a;

JSON_DATA
-------------------------------------------------------
{"deptnoCol":10,"dnameCol":"ACCOUNTING"}
{"deptnoCol":20,"dnameCol":"RESEARCH"}
{"deptnoCol":30,"dnameCol":"SALES"}
{"deptnoCol":40,"dnameCol":"OPERATIONS"}


SQL>SELECT JSON_OBJECT(a.*) AS json_data
FROM   (SELECT deptno AS "deptnoCol",
               dname AS "dnameCol"
        FROM   dept) a;

JSON_DATA
-------------------------------------------------------
{"deptnoCol":10,"dnameCol":"ACCOUNTING"}
{"deptnoCol":20,"dnameCol":"RESEARCH"}
{"deptnoCol":30,"dnameCol":"SALES"}
{"deptnoCol":40,"dnameCol":"OPERATIONS"}

SQL>