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PostgreSQLとOracleのsql差异

时间:2021-07-01 10:21:17 帮助过:36人阅读

 

1.rownum

(1)Oracle分页查询使用rownum,PostgreSQL使用limit offset

ORACLEPOSTGRESQL
select * from (select rownum r,e.* from emp e where rownum <=5) t where r>0; select * from emp limit 5 offset 0;

 

 

 

(2)Oracle中rownum=1,PostgreSQL中使用limit 1

ORACLEPOSTGRESQL
select * from emp where rownum = 1; select * from emp limit 1;

 

 

 

(3)Oracle中序号列rownum,PostgreSQL使用窗口函数

ORACLEPOSTGRESQL
select rownum,t.* from emp t; select row_number() over(), t.* from emp t;

 

 

 

2.系统日期

ORACLEPOSTGRESQL
SYSDATE current_timestamp, current_date

 

 

 

3.delete语句

Oracle delete语句可以没有from,pg必须要有from

ORACLEPOSTGRESQL
delete from emp where empno = xxx; delete emp where empno = xxx delete from emp where empno = xxx

 

 

 

4.类型自动转换

Oracle支持类型自动转换,例如数字自动换换为字符串等;PG中需要显示转换,或者添加CAST

 

5.子查询别名

PostgreSQL在from关键字后的子查询必须要有别名,Oralce可以没有。

 

6. group by having

PG having语句必须在group by之后,oracle可以在group by之前

 

7.递归查询

Oracle中使用start with … connect by…, PG中使用with recusive

ORACLEPOSTGRESQL
select * from larearrelation where rearedgens = 1 and rearflag = 1 and rearlevel = ‘01’ connect by prior agentcode = rearagentcode start with rearagentcode = ‘10032226’; with recursive rs as ( select * from larearrelation where rearagentcode = ‘10032226’ union all select a. *from larearrelation a, rs where a.rearagentcode = rs.agentcode ) select ** from rs where rearedgens = 1 and rearflag = ‘1’ and rearlevel = ‘01’

  

8.update语句别名

postgresql中update语句时,set的字段不能有别名

ORACLEPOSTGRESQL
update emp t set t.name = ‘xxx’ where t.empno = 2 update emp set name = ‘xxx’ where empno = 2

 

 

 

9. 日期相减

oracle日期相减自动转换为数字,结果为相差的天数。 pg日期相减为interval类型,得到相差天数需要进行类型转换

 

10.递归查询中的level

oracle的递归查询中level表示查询深度(或者递归层次),在PG中没有此含义的关键字,需要自行在with recursive实现

ORACLEPOSTGRESQL
select max(level) from larearrelation where rearedgens = 1 and rearflag = 1 and rearlevel = ‘01’ connect by prior agentcode = rearagentcode start with rearagentcode = ‘10032226’; with recursive rs as ( select larearrelation.*, 1 depth from larearrelation where rearagentcode = ‘10032226’ union all select a./**, rs.depth + 1 depth from larearrelation a, rs where a.rearagentcode = rs.agentcode ) select max(rs.depth) from rs where rearedgens = 1 and rearflag = ‘1’ and rearlevel = ‘01’

 

 11.序列的调用

ORACLEPOSTGRESQL
select seqname.nextval from dual; select nextval(‘seqname’)

 

 

 

12.外连接

Oralce外连接支持使用 (+), PostgreSQL需使用left jion或者right join标准sql语法

 

13.distinct去重复

oracle支持unique关键字去重复,pg中只能使用distinct

 

14.字符串分割

ORACLEPOSTGRESQL
listagg string_agg

 

 

 

15.集合相减

ORACLEPOSTGRESQL
Minus except

 

 

 

16.null与 ‘‘

null和’’在oracle中是一致的,最终都会存储为null,在PG中会进行区分

 

17.不等于

Oracle中 ! =< >操作符中间允许有空格,PG中不可以

 

18.别名

PG中无效的别名,可以尝试加as关键字,例如name

 

19.正则表达式

ORACLEPOSTGRESQL
SELECT REGEXP_SUBSTR(‘17,20,23’,’,+’,1,1,’i’) FROM DUAL; select (regexp_matches(‘17,20,23’, ‘,+’))[1]

 

 

 

20.字段大小写

oracle字段名大写,PG字段名小写

 

 

PostgreSQLとOracleのsql差异

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