PostgreSQLとOracleのsql差异

2015-04-14 13:16

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PostgreSQLとOracleのsql差异
[数据库教程]

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

ORACLE	POSTGRESQL
select * from emp where rownum = 1;	select * from emp limit 1;

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

ORACLE	POSTGRESQL
SYSDATE	current_timestamp, current_date

Oracle delete语句可以没有from，pg必须要有from

ORACLE	POSTGRESQL
delete from emp where empno = xxx; delete emp where empno = xxx	delete from emp where empno = xxx

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

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

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

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

ORACLE	POSTGRESQL
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’

postgresql中update语句时，set的字段不能有别名

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

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

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

ORACLE	POSTGRESQL
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’