PostgreSQL和Oracle用法上的一些区别
（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;
当a 或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 以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 X ，offset Y 方法, 而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 到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：‘999999’ —- 6 位数为COL1 字段的长度]
（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
在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。
转载自：https://blog.csdn.net/wanghai__/article/details/5515570
