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  • PostgreSQL与Oracle的区别

    NO 问题点 Oracle PostgreSQL
    1 DUAL SELECT 1+1 FROM DUAL SELECT 1+1
    或者
    CREATE VIEW dual AS
          SELECT 'X'::VARCHAR(1) AS DUMMY
    再 SELECT 1+1 FROM DUAL
    2 NEXTVAL SELECT A_TABLE_SEQUENCE.NEXTVAL
    FROM   DUAL    		 SELECT NEXTVAL('A_TABLE_SEQUENCE')
    FROM   DUAL
    3 ROWNUM ①SELECT *
    FROM AGE_TYPE
    WHERE ROWNUM<=5    		 ①SELECT *
    FROM AGE_TYPE
    LIMIT 5 OFFSET 0
    ②SELECT *
    FROM AGE_TYPE
    WHERE CODE IS NOT NULL
    AND ROWNUM<=5
    ORDER BY CODE DESC    		 ②SELECT *
    FROM
    AGE_TYPE
    WHERE CODE IS NOT NULL
    ORDER BY CODE DESC
    LIMIT 5 OFFSET 0
    4 (+) ①SELECT *
    FROM A_TABLE A , B_TABLE B
    WHERE A.ID(+)=B.ID    		 ①SELECT *
    FROM A_TABLE A
    RIGHT OUTER JOIN
    B_TABLE B
    ON A.ID=B.ID
    ②SELECT *
    FROM A_TABLE A , B_TABLE B
    WHERE A.ID(+)=B.ID
    AND A.COL1='COL1_VALUE'    		 ②SELECT *
    FROM A_TABLE A
    RIGHT OUTER JOIN B_TABLE B
    ON A.ID=B.ID AND A.COL1='COL1_VALUE'
    ③SELECT *
    FROM A_TABLE A, B_TABLE B,C_TABLE C,D_TABLE D
    WHERE
    A.ID=B.ID(+) AND
    A.ID=C.ID(+) AND
    A.COL1=D.COL1    		 ③SELECT *
    FROM (A_TABLE A
    LEFT OUTER JOIN B_TABLE B
    ON A.ID=B.ID)
    LEFT OUTER JOIN C_TABLE C
    ON A.ID=C.ID,D_TABLE D
    WHERE A.COL1=D.COL1
    ④!!!
    SELECT *
    FROM A_TABLE A
    WHERE A.COL1(+)=0 AND
     A.COL2(+) ='A_VALUE2'    		 ④!!!
    SELECT *
    FROM A_TABLE A
    WHERE A.COL1=0 AND
     A.COL2='A_VALUE2'
    WHERE (A.COL1=0 OR A.COL1 IS NULL) AND
     (A.COL2='A_VALUE2' OR A.COL2 IS NULL)
    5 AS SELECT A.COL1 A_COL1,
               A.COL2 A_COL2
    FROM A_TABLE A    		 SELECT A.COL1 AS A_COL1,
               A.COL2 AS A_COL2
    FROM A_TABLE A
    6 NVL SELECT NVL(SUM(VALUE11),0) FS_VALUE1,
                NVL(SUM(VALUE21),0) FS_VALUE2
    FROM   FIELD_SUM     		 SELECT COALESCE(SUM(VALUE11),0) AS FS_VALUE1,
               COALESCE(SUM(VALUE21),0) AS FS_VALUE2
    FROM   FIELD_SUM 
    7 TO_
    NUMBER    		 SELECT COL1
    FROM A_TABLE
    ORDER BY TO_NUMBER(COL1)    		 SELECT COL1
    FROM A_TABLE
    ORDER BY TO_NUMBER(COL1,999999)
    [注：'999999' ---- 6位数为COL1字段的长度]
    8 DECODE SELECT DECODE(ENDFLAG,'1','A','B') ENDFLAG
    FROM TEST    		 SELECT
    (CASE ENDFLAG
    WHEN '1' THEN 'A'
    ELSE 'B' END) AS ENDFLAG
    FROM TEST
    9 时间
    问题    		 UPDATE A_TABLE
    SET ENTREDATE=SYSDATE    		 UPDATE A_TABLE
    SET ENTREDATE=TO_TIMESTAMP(CURRENT_TIMESTAMP,'YYYY-MM-DD HH24:MI:SS')
    或者
    UPDATE A_TABLE
    SET ENTREDATE=CURRENT_TIMESTAMP
    SELECT TO_DATE('20010203','YYYY-MM-DD') AS DAY
    FROM DUAL    		 SELECT TO_DATE('20010203','YYYYMMDD') AS DAY
    FROM DUAL
    SELECT TO_DATE('20010203','YYYY-MM-DD') AS DAY
    FROM DUAL
    SELECT TO_DATE(SYSDATE,'YYYY-MM-DD') AS DAY
    FROM DUAL    		 SELECT TO_DATE(CURRENT_DATE,'YYYY-MM-DD') AS DAY
    FROM DUAL
    SELECT TO_DATE(SYSDATE,'YYYY/MM/DD') AS DAY
    FROM DUAL    		 SELECT TO_DATE(CURRENT_DATE,'YYYY/MM/DD') AS DAY
    FROM DUAL
    10 || SELECT NULL||'-'||NULL AS VALUES1
    FROM DUAL
    		 SELECT COALESCE(NULL,'')||'-'||COALESCE(NULL,'') AS VALUES1
    FROM DUAL
    SELECT NULL||'-' ||NULL AS VALUES1
    FROM DUAL
    11 aggregate SELECT ROUND(AVG(SUM(BASICCNT1))) BASICCNT
    FROM   ACCESS_INFO_SUM1_V
    WHERE YEARCODE BETWEEN '200305' AND '200505'
    GROUP BY SCCODE    		 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
    12 「"」 ①SELECT LENGTH('') AS VALUE1 FROM DUAL
    [Result]VALUE1=NULL    		 ①SELECT LENGTH('') AS VALUE1 FROM DUAL
    [Result]VALUE1=0
    ②SELECT TO_DATE('','YYYYMMDD') AS VALUE2
    FROM DUAL
    [Result]VALUE2=NULL    		 ②SELECT TO_DATE('','YYYYMMDD') AS VALUE2
    FROM DUAL
    [Result]VALUE2=0001-01-01 BC
    ③SELECT TO_NUMBER('',1) AS VALUE3 FROM DUAL
    [Result]VALUE3=NULL    		 ③SELECT TO_NUMBER('',1) AS VALUE3 FROM DUAL
    [Result]不能执行
    ④INSERT INTO TEST(VALUE4)VALUES('')
    [Result]VALUE4=NULL (注：VALUE3字段为数值类型)    		 ④INSERT INTO TEST(VALUE4)VALUES('')
    [Result]VALUE4=0
     (注：VALUE4字段为数值类型)
    ⑤INSERT INTO TEST(VALUE5)VALUES('')
    [Result]VALUE5=NULL (注：VALUE5字段为字符类型)    		 ⑤INSERT INTO TEST(VALUE5)VALUES('')
    [Result]VALUE5=''
     (注：VALUE5字段为字符类型,结果为长度为零的字符串)
    ⑥INSERT INTO TEST(VALUE6)VALUES(TO_DATE('','YYYYMMDD'))
    [Result]VALUE6=NULL (注：VALUE6字段为时间类型)    		 ⑥INSERT INTO TEST(VALUE6)VALUES(TO_DATE('','YYYYMMDD'))
    [Result]VALUE6=0001-01-01 BC
     (注：VALUE7字段为时间类型)
    13 CEIL SELECT CEIL(SYSDATE - TO_DATE('20051027 14:56:10','YYYYMMDD HH24:MI:SS')) AS DAYS
    FROM DUAL    		 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
    14 NULLIF 无NULLIF函数 SELECT NULLIF(VALUE1,VALUE2) AS COL1 FROM DUAL
    [注]当VALUE1=VALUE2时，COL1=NULL
    15 CONCAT CONCAT(CHAR,CHAR) 创建函数来解决
    CREATE FUNCTION CONCAT(CHAR,CHAR)
    RETURNS CHAR AS
            'SELECT $1 || $2' LANGUAGE 'sql';
    16 ADD_
    MONTHS    		 add_months(date, int) 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'
    17 LAST
    _DAY    		 LAST_DAY(DATE) 创建函数来解决
    CREATE FUNCTION LAST_DAY(DATE)
    RETURNS DATE AS
            'SELECT date(substr(text($1 +
                    interval(''1 month'')),1,7)||''-01'')-1'
            LANGUAGE 'sql';
    18 MONTHS
    _BETWEEN    		 MONTH_BETWEEN(DATA,DATA) 创建函数来解决
    CREATE FUNCTION MONTH_BETWEEN(DATA,DATA)
    RETURNS NUMERIC AS
            'SELECT to_number((date($1)-
                               date($2)),''999999999'')/31'
            LANGUAGE 'sql';
    19 GRE~
    ATEST    		 GREATEST (LEAST) 创建函数来解决
    CREATE OR REPLACE FUNCTION
       GREATEST(TEXT[]) RETURNS TEXT AS '
    DECLARE
       ARRY ALIAS FOR $1;
       GREATEST TEXT;
    BEGIN
       GREATEST := ARRY[1];
       FOR I IN 1 .. ARRAY_UPPER(ARRY,1) LOOP
          IF ARRY[I] > GREATEST THEN
            GREATEST := ARRY[I];
          END IF;
       END LOOP;
       RETURN GREATEST;
    END;
    ' LANGUAGE 'PLPGSQL';

    SELECT GREATEST( ARRAY['HARRY','HARRIOT','HAROLD'])
    AS "Greatest";
    20 BITAND BITAND(int,int) SELECT 値 & 値;
    21 子条件 　 在FROM子条件中字段须有列名，
    处理方法用AS +别名
    22 MINUS MINUS 以EXCEPT来替代
    23 BIN_
    TO_
    NUM    		 SELECT BIN_TO_NUM(1,0,1,0) AS VALUE1 FROM DUAL SELECT CAST(B'1010' AS INTEGER) AS VALUE1