目录
环境
文档用途
详细信息

环境
系统平台：Linux x86-64 Red Hat Enterprise Linux 7
版本：6.0,5.6.5,4.5,4.3.4.9
文档用途
从MySQL数据库迁移到瀚高数据库，瀚高数据库中没有date_format函数，为满足客户需求需要自定义同名兼容函数。

详细信息

--date_format函数主体：

CREATE OR REPLACE FUNCTION date_format(timestamp without time zone, text)
 RETURNS text
 LANGUAGE plpgsql
 IMMUTABLE STRICT
AS $function$
  DECLARE
    i int := 1;
    temp text := '';
    c text;
    n text;
    res text;
  BEGIN
    WHILE i <= pg_catalog.length($2) LOOP
      c := SUBSTRING ($2 FROM i FOR 1);
      IF c = '%' AND i != pg_catalog.length($2) THEN
        n := SUBSTRING ($2 FROM (i + 1) FOR 1);
        SELECT INTO res CASE
          WHEN n = 'a' THEN pg_catalog.to_char($1, 'Dy') 
          WHEN n = 'b' THEN pg_catalog.to_char($1, 'Mon') 
          WHEN n = 'c' THEN pg_catalog.to_char($1, 'FMMM') 
          WHEN n = 'D' THEN pg_catalog.to_char($1, 'FMDDth') 
          WHEN n = 'd' THEN pg_catalog.to_char($1, 'DD') 
          WHEN n = 'e' THEN pg_catalog.to_char($1, 'FMDD') 
          WHEN n = 'f' THEN pg_catalog.to_char($1, 'US') 
          WHEN n = 'H' THEN pg_catalog.to_char($1, 'HH24') 
          WHEN n = 'h' THEN pg_catalog.to_char($1, 'HH12') 
          WHEN n = 'I' THEN pg_catalog.to_char($1, 'HH12')      
          WHEN n = 'i' THEN pg_catalog.to_char($1, 'MI') 
          WHEN n = 'j' THEN pg_catalog.to_char($1, 'DDD') 
          WHEN n = 'k' THEN pg_catalog.to_char($1, 'FMHH24') 
          WHEN n = 'l' THEN pg_catalog.to_char($1, 'FMHH12') 
          WHEN n = 'M' THEN pg_catalog.to_char($1, 'FMMonth') 
          WHEN n = 'm' THEN pg_catalog.to_char($1, 'MM') 
          WHEN n = 'p' THEN pg_catalog.to_char($1, 'AM') 
          WHEN n = 'r' THEN pg_catalog.to_char($1, 'HH12:MI:SS AM') 
          WHEN n = 'S' THEN pg_catalog.to_char($1, 'SS')
          WHEN n = 's' THEN pg_catalog.to_char($1, 'SS')
          WHEN n = 'T' THEN pg_catalog.to_char($1, 'HH24:MI:SS') 
          WHEN n = 'U' THEN pg_catalog.lpad(week($1::date, 0)::text, 2, '0')
          WHEN n = 'u' THEN pg_catalog.lpad(week($1::date, 1)::text, 2, '0')
          WHEN n = 'V' THEN pg_catalog.lpad(week($1::date, 2)::text, 2, '0')
          WHEN n = 'v' THEN pg_catalog.lpad(week($1::date, 3)::text, 2, '0')
          WHEN n = 'W' THEN pg_catalog.to_char($1, 'FMDay') 
          WHEN n = 'w' THEN EXTRACT(DOW FROM $1)::text
          WHEN n = 'X' THEN pg_catalog.lpad(((_calc_week($1::date, _week_mode(2)))[2])::text, 4, '0')
          WHEN n = 'x' THEN pg_catalog.lpad(((_calc_week($1::date, _week_mode(3)))[2])::text, 4, '0')
          WHEN n = 'Y' THEN pg_catalog.to_char($1, 'YYYY') 
          WHEN n = 'y' THEN pg_catalog.to_char($1, 'YY')
          WHEN n = '%' THEN pg_catalog.to_char($1, '%')
          ELSE NULL
        END;
        temp := temp operator(pg_catalog.||) res;
        i := i + 2;
      ELSE
        temp = temp operator(pg_catalog.||) c;
        i := i + 1;
      END IF; 
    END LOOP;
    RETURN temp;
  END
$function$;


--主体函数调用的其它函数

CREATE OR REPLACE FUNCTION _week_mode(mode integer)
RETURNS integer AS $$
  DECLARE
    _WEEK_MONDAY_FIRST  CONSTANT integer := 1;
    _WEEK_FIRST_WEEKDAY CONSTANT integer := 4;
    week_format integer := mode & 7;
  BEGIN
    IF (week_format & _WEEK_MONDAY_FIRST) = 0 THEN
      week_format := week_format # _WEEK_FIRST_WEEKDAY;
    END IF;

    RETURN week_format;
  END;
$$ IMMUTABLE STRICT LANGUAGE PLPGSQL;

CREATE OR REPLACE FUNCTION _calc_weekday(qdate date, sundayfirst boolean)
RETURNS integer AS $$
  BEGIN
    RETURN (EXTRACT(DOW FROM qdate)::integer + CASE WHEN sundayfirst THEN 0 ELSE 6 END) % 7;
  END;
$$ IMMUTABLE STRICT LANGUAGE PLPGSQL;

CREATE OR REPLACE FUNCTION _calc_days_in_year(year integer)
RETURNS integer AS $$
  BEGIN
    IF (year & 3) = 0 AND ((year % 100) <> 0 OR (year % 400) = 0 AND year <> 0) THEN
      RETURN 366;
    ELSE
      RETURN 365;
    END IF;
  END;
$$ IMMUTABLE STRICT LANGUAGE PLPGSQL;

CREATE OR REPLACE FUNCTION _calc_week(qdate anyelement, behavior integer)
RETURNS integer[] AS $$
  DECLARE
    _WEEK_MONDAY_FIRST  CONSTANT integer := 1;
    _WEEK_YEAR          CONSTANT integer := 2;
    _WEEK_FIRST_WEEKDAY CONSTANT integer := 4;
    qyear         integer := EXTRACT(YEAR FROM qdate);
    qmonth        integer := EXTRACT(MONTH FROM qdate);
    qday          integer := EXTRACT(DAY FROM qdate);
    daynr         integer := EXTRACT(DOY FROM qdate);
    yday1         date    := pg_catalog.date_trunc('year', qdate);
    first_daynr   integer := 1;
    monday_first  boolean := (behavior & _WEEK_MONDAY_FIRST) <> 0;
    week_year     boolean := (behavior & _WEEK_YEAR) <> 0;
    first_weekday boolean := (behavior & _WEEK_FIRST_WEEKDAY) <> 0;
    weekday       integer := _calc_weekday(yday1, NOT monday_first);
    days          integer;
  BEGIN
    IF qmonth = 1 AND qday <= 7 - weekday THEN
      IF (NOT week_year) AND ((first_weekday AND weekday <> 0) OR (NOT first_weekday AND weekday >= 4)) THEN
        RETURN array[0, qyear];
      END IF;

      week_year := true;
      qyear := qyear - 1;
      days := _calc_days_in_year(qyear);
      first_daynr := first_daynr - days;
      weekday := (weekday + 53 * 7 - days) % 7;
    END IF;

    IF (first_weekday AND weekday <> 0) OR (NOT first_weekday AND weekday >= 4) THEN
      days := daynr - (first_daynr + (7 - weekday));
    ELSE
      days := daynr - (first_daynr - weekday);
    END IF;

    IF week_year AND days >= 52 * 7 THEN
      weekday := (weekday + _calc_days_in_year(qyear)) % 7;
      IF (NOT first_weekday AND weekday < 4) OR (first_weekday AND weekday = 0) THEN
	qyear := qyear + 1;
        RETURN array[1, qyear];
      END IF;
    END IF;

    RETURN array[days / 7 + 1, qyear];
  END;
$$ IMMUTABLE STRICT LANGUAGE PLPGSQL;


CREATE OR REPLACE FUNCTION week(anyelement, integer)
 RETURNS integer
 LANGUAGE plpgsql
 IMMUTABLE STRICT
AS $function$
BEGIN
	IF is_datetime ( $1 ) THEN
		RETURN (_calc_week($1, _week_mode($2)))[1];
	END IF;
	RAISE EXCEPTION 'Invalid date / time value --> %', $1;
END;
$function$;
--调用函数：

select DATE_FORMAT(now()::timestamp ,'%Y-%m-%d');
select DATE_FORMAT(now()::timestamp,'%Y-%m-%d %H:%i');
select DATE_FORMAT(now()::timestamp,'%Y');
select DATE_FORMAT(now()::timestamp,'%Y-%m');
select DATE_FORMAT(now()::timestamp,'%m-%d');
select DATE_FORMAT(now()::timestamp,'%m-%d %H:%i');
select DATE_FORMAT(now()::timestamp,'%Y年%m月%d日');
select DATE_FORMAT(now()::timestamp,'%Y-%m-%d %H:%i:%s');