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68.Postgresql与oracle用法的一些区别

Oracle 作者:soho20080721 时间:2014-03-07 10:45:05 0 删除 编辑

1 ) 注意增加约束时的写法,和ORACLE 略有不同

Oracle 

ALTER TABLE SCHEMA.PREFIX_INFO ADD (
CONSTRAINT PK_PREFIX_INFO PRIMARY KEY (INFO_ID));

PostgresQL 

alter table schema.prefix_info add constraint prefix_info_pkey primary key(info_id);

2 )系统默认的最大值与ORACLE 不同

Oracle 

CREATE SEQUENCE PREFIX_INFO_SEQUENCE
INCREMENT BY 1 
START WITH 582
MINVALUE 1 
MAXVALUE 9999999999999999999999999999 
NOCYCLE 
CACHE 20 
NOORDER;

PostgresQL 

CREATE SEQUENCE schema.prefix_info_sequence
increment 1
minvalue 1
maxvalue 9223372036854775807
start 582
cache 20;

3 PostgresQL 中的 || 用 法与其他数据库不同:
select a|| b from table1;
a b 其中一个为null 时, 该查询返回null 

4 PostgresQL 中没有concat 函数,且由于|| 用法的问题,无法使用|| 替换,解决 方法为在public schema 中创建函数concat

create or replace function concat(text, text)
returns text as
$body$select coalesce($1,'') || coalesce($2,'')$body$
language 'sql' volatile;
alter function concat(text, text) owner to postgres;

-- 无需特殊授权即可在其他schema 中使用

4 PostgresQL 中没有dual 虚拟表,为保 证程序兼容性,可创建伪视图(view )替代:

CREATE OR REPLACE VIEW dual AS 
SELECT NULL::"unknown"
WHERE 1 = 1;

ALTER TABLE dual OWNER TO postgres;
GRANT ALL ON TABLE dual TO postgres;
GRANT SELECT ON TABLE dual TO public;

必须授权public select 权 限

5 )关联查询用法区别

ORACLE:

简单外连接:
SELECT COUNT(DISTINCT(A.COL1)) AS RCOUNT FROM 
SCHEMA.PREFIX_TABLE1 A,SCHEMA.PREFIX_TABLE2 B
WHERE 1 = 1 
AND A.COL2 = B.COL2(+)
AND A.COL3 > 0 
AND A.COL4 = '1'

超级变态外连接:
SELECT COUNT(DISTINCT(A.COL1)) AS RCOUNT FROM 
SCHEMA.PREFIX_TABLE1 A,SCHEMA.PREFIX_TABLE2 B,SCHEMA.PREFIX_TABLE3 C,SCHEMA.PREFIX_TABLE4 D 
WHERE 1 = 1 
AND A.COL2 = B.COL2 
AND A.COL3 = C.COL3(+) 
AND A.COL4 = D.COL4(+)
AND A.COL5 > 0 
AND A.COL6 = '1'


POSTGRESQL:

简单外连接:
select count(distinct(a.col1)) as rcount from 
schema.prefix_table1 a left outer join schema.prefix_table2 b on (a.col2 = b.col2)
where 1 = 1 
and a.col3 > 0 
and a.col4 = '1'

超级变态外连接:
select count(distinct(a.col1)) as rcount from 
schema.prefix_table1 a inner join schema.prefix_table2 b on (a.col2 = b.col2) 
left outer join schema.prefix_table3 c on (a.col3 = c.col3) 
left outer join schema.prefix_table4 d on (a.col4 = d.col4) 
where 1 = 1 
and a.col5 > 0 
and a.col6 = '1'

6 PostgresQL 中子查询较为规范,子查询结果集必须拥有alias

ORACLE:
SELECT * FROM (
SELECT * FROM (
SELECT * FROM SCHEMA.PREFIX_TABLE ORDER BY COL1
) WHERE X=1 ORDER BY COL2
) WHERE Y=2 ORDER BY COL3

POSTGRESQL:

SELECT * FROM (
SELECT * FROM (
SELECT * FROM SCHEMA.PREFIX_TABLE ORDER BY COL1 ALIAS1
) WHERE X=1 ORDER BY COL2 ALIAS2
) WHERE Y=2 ORDER BY COL3

7  PostgresQL 中没有rownum ,无法 使用where rownum < = X 的方法进行分页,取而代之的是limit Xoffset Y 方法, ORACLE 中不允许使用LIMIT X 的 方法
ORACLE:

SELECT * FROM ( SELECT * FROM (SELECT * FROM SCHEMA.PREFIX_TABLE1 ORDER BY COL1 DESC,COL2 ASC) where ROWNUM <= 50 ORDER BY COL3 ASC,COL4 DESC)
WHERE ROWNUM <= 20 ORDER BY COL5 DESC,COL6 ASC;

POSTGRES:

select * from ( select * from (SELECT * FROM SCHEMA.PREFIX_TABLE1 ORDER BY COL1 DESC,COL2 ASC) selb order by col3 asc,col4 desc limit 50 ) sela
order by col5 desc,col6 asc limit 20;

-- 注意!!limit 必须用于order by 之后

-- 例:取1 50 条数据

select * from VOIP_FEE_RATE temp offset 0 limit 50

8 )序列使用的区别

ORACLE:
SELECT SCHEMA.PREFIX_TABLE1_SEQUENCE.NEXTVAL AS nCode FROM DUAL

POSTGRES:
SELECT NEXTVAL('SCHEMA.PREFIX_TABLE1_SEQUENCE') AS nCode FROM DUAL 
--
 注意,此方法前提是dual 视图已建立,如没有,可省略FROM DUAL

9 )字段取别名必须用as
Oracle -- SELECT A.COL1 A_COL1
 A.COL2 A_COL2 FROM A_TABLE A
Postgresql---- SELECT A.COL1 AS A_COL1
 A.COL2 AS A_COL2 FROM A_TABLE A

10 NVL 用法
Oracle --SELECT NVL(SUM(VALUE11),0) FS_VALUE1, NVL(SUM(VALUE21),0) FS_VALUE2 FROM   FIELD_SUM 
Postgresql--SELECT COALESCE(SUM(VALUE11),0) AS FS_VALUE1,COALESCE(SUM(VALUE21),0) AS FS_VALUE2
FROM FIELD_SUM

11 TO_NUMBER 用法
Oracle -- SELECT COL1 FROM A_TABLE ORDER BY TO_NUMBER(COL1)
Postgresql- select TO_NUMBER(COL1,'99G999D9S') from A_TABLE
    注:'99G999D9S'就直接写到查询语句里面。

 

12 DECODE 用法
Oracle -- SELECT DECODE(ENDFLAG,'1','A','B') ENDFLAGFROM TEST
Postgresql- SELECT (CASEENDFLAG WHEN '1' THEN 'A'ELSE 'B' END) AS ENDFLAG FROM TEST

13 )统计 相关 用法
Oracle -- SELECT ROUND(AVG(SUM(BASICCNT1))) BASICCNT FROM   ACCESS_INFO_SUM1_V
WHERE YEARCODE BETWEEN '200305' AND '200505' GROUP BY SCCODE

Postgresql-- SELECT ROUND(AVG(AIV.BASICCNT)) AS BASICCNT FROM ( SELECT SUM(BASICCNT1) AS BASICCNT
FROM   ACCESS_INFO_SUM1_V WHERE YEARCODE BETWEEN '200305' AND '200505' GROUP BY sccode ) AIV

14 )时间计算 用法
Oracle -- SELECT CEIL(SYSDATE - TO_DATE('20051027 14:56:10','YYYYMMDD HH24:MI:SS')) AS DAYS
FROM DUAL 
Postgresql-- SELECT EXTRACT(DAY FROM (TO_TIMESTAMP(CURRENT_TIMESTAMP,'YYYY-MM-DD-HH24-MI-SS') - TO_TIMESTAMP('2005-10-27 14:56:10','YYYY-MM-DD-HH24-MI-SS') ))+1 AS DAYS FROM DUAL
Oracle -- add_months(date, int)
Postgresql--
 创建函数来解决
CREATE FUNCTION add_months(date, int) 
RETURNS date AS 
'SELECT ($1 + ( $2::text || ''months'')::interval)::date;' 
LANGUAGE 'sql'
 

(15)关于事务

 

PostgreSQL中,默认情况下,一条SQL语句是一个独立的事务。在一条SQL语句开始执行时,PostgreSQL自动为其创建一个事务。如果语句执行成功,PostgreSQL自动提交该语句的事务,否则回滚事务。

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