PostgresQL 学习记录之与oracle区别(二)
（9）字段取别名必须用asOracle -- SELECT A.COL1A_COL1，A.COL2A_COL2 FROM A_TABLE A
Postgresql---- SELECT A.COL1 AS A_COL1，A.COL2 AS A_COL2FROM 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
FROMFIELD_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') ENDFLAGFROMTEST
Postgresql- SELECT (CASEENDFLAGWHEN '1' THEN 'A'ELSE 'B' END) AS ENDFLAG FROM TEST
（13）统计 相关 用法
Oracle -- SELECT ROUND(AVG(SUM(BASICCNT1))) BASICCNTFROM ACCESS_INFO_SUM1_V
WHERE YEARCODE BETWEEN '200305' AND '200505'GROUP BY SCCODE
Postgresql-- SELECTROUND(AVG(AIV.BASICCNT)) AS BASICCNTFROM(SELECT SUM(BASICCNT1)AS BASICCNT
FROM ACCESS_INFO_SUM1_VWHERE 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-- SELECTEXTRACT(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 DAYSFROMDUAL
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'
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