oracle (+)学习

news2024/11/27 0:33:24

最近工作需要将oracle的存储过程转化为hive的sql脚本。遇到很多不一样的地方，例如oracle连接中有(+)号的用法。

借鉴这篇文章，但是这个排版比较烂。。。

oracle (+)的,Oracle中(+)的作用_大雪菜的博客-CSDN博客

先建表和插入数据

--生成部门表

CREATE TABLE Test_Departments
(
depID NUMBER(38,0),
depName VARCHAR2(20),
delFlag NUMBER(1,0)
);

--生成员工表
CREATE TABLE Test_Employees
(
empID NUMBER(38,0),
empName VARCHAR2(20),
depID NUMBER(38,0),
delFlag NUMBER(1,0)
);

--插入测试数据
INSERT INTO Test_Departments VALUES(1,'FI',0);
INSERT INTO Test_Departments VALUES(2,'MA',0);
INSERT INTO Test_Departments VALUES(3,'HR',1);
INSERT INTO Test_Departments VALUES(4,'IT',0);
INSERT INTO Test_Employees VALUES(1,'wbq',1,0);
INSERT INTO Test_Employees VALUES(2,'czh',2,0);
INSERT INTO Test_Employees VALUES(3,'chh',1,0);
INSERT INTO Test_Employees VALUES(4,'wal',2,0);
INSERT INTO Test_Employees VALUES(5,'ddd',3,0);

首先说明(+)代表什么？代表这一侧的数据可以为空！ a.id=b.id(+) 代表b表和a表关联的时候以a表作为主表。

测试1 这个是最常用的做法以a为主表

SELECT A.*, B.*
FROM Test_Departments A
LEFT JOIN Test_Employees B ON A.depID = B.depID

等价于

SELECT A.*, B.*
FROM Test_Departments A, Test_Employees B
WHERE A.depID = B.depID(+)

测试2 还是以a做主表，仍然保留a的所有数据

SELECT A.*, B.*
FROM Test_Departments A
LEFT JOIN Test_Employees B ON A.depID = B.depID
AND B.depID = 3

等价于

SELECT A.*, B.*
FROM Test_Departments A, Test_Employees B
WHERE A.depID = B.depID(+)
AND (B.depID(+) = 3)

这里涉及到一个 left join 后面的过滤条件是on和where 的问题

select A.*,B.* from A left join B on A.id=B.id and B.id=3

返回结果：显示A表所有数据，B.id=3的数据，B.id不等于3的默认为空

select A.*,B.* from A,B where A.id=B.id(+) and B.id=3

返回结果：仅仅显示B.id=3的一条数据

测试3 保留a为主表，但是只显示过滤条件的数据

SELECT A.*, B.*
FROM Test_Departments A
LEFT JOIN Test_Employees B ON A.depID = B.depID
WHERE B.depID = 3

等价于

SELECT A.*, B.*
FROM Test_Departments A, Test_Employees B
WHERE A.depID = B.depID(+)
AND (B.depID = 3)