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PL/SQL function that converts Gregorian dates to Hijri

FUNCTION Georgian2Hijri(G_DATE Date) RETURN Varchar2 IS H_DAY NUMBER(2):=0; HDAY VARCHAR2(2); H_MONTH NUMBER(2):=1; HMONTH VARCHAR2(2); H_YEAR NUMBER(4):=1; FGDATE DATE; I_LOOP NUMBER; HY NUMBER; MONTH_NAME VARCHAR2(40); BEGIN FGDATE := TO_DATE('14-07-0622','DD-MM-YYYY'); I_LOOP := G_DATE - FGDATE; LOOP IF I_LOOP<355 THEN EXIT; END IF; HY := TRUNC( H_YEAR / 30 ) * 30; IF (H_YEAR - HY) IN (2,5,7,10,13,16,18,21,24,26,29) THEN H_YEAR := H_YEAR + 1; I_LOOP := I_LOOP - 355; ELSE I_LOOP := I_LOOP - 354; H_YEAR := H_YEAR + 1; END IF; END LOOP; FOR I IN 1..I_LOOP LOOP H_DAY := H_DAY + 1; IF (H_MONTH=1 OR H_MONTH=3 OR H_MONTH=5 OR H_MONTH=7 OR H_MONTH=9 OR H_MONTH=11) AND H_DAY>30 THEN H_MONTH := H_MONTH + 1; H_DAY := 1; END IF; IF (H_MONTH=2 OR H_MONTH=4 OR H_MONTH=6 OR H_MONTH=8 OR H_MONTH=10)AND H_DAY>29 THEN H_MONTH := H_MONTH + 1; H_DAY := 1; END IF; HY := TRUNC( H_YEAR / 30 ) * 30; IF (H_YEAR - HY) IN (2,5,7,10,13,16,18,21,24,26,29) THEN IF H_MONTH=12 AND H_DAY>30 THEN H_MONTH := H_MONTH + 1; H_DAY := 1; IF H_MONTH>12 THEN H_YEAR := H_YEAR + 1; H_MONTH := 1; END IF; END IF; ELSE IF H_MONTH=12 AND H_DAY>29 THEN H_MONTH := H_MONTH + 1; H_DAY := 1; IF H_MONTH>12 THEN H_YEAR := H_YEAR + 1; H_MONTH := 1; END IF; END IF; END IF; END LOOP; SELECT DECODE(H_MONTH ,1,'محرم' ,2,'صفر' ,3,'ربيع الأول' ,4,'ربيع الثاني ,5,'جمادى الأولى ,6,'جمادة الآخرة ,7,'رجب' ,8,'شعبان' ,9,'رمضان' ,10,'شوال' ,11,'ذي القعدة' ,12,ذي الحجة',NULL) INTO MONTH_NAME FROM DUAL; IF H_DAY<10 THEN HDAY := '0' || TO_CHAR(H_DAY); ELSE HDAY := TO_CHAR(H_DAY); END IF; IF H_MONTH<10 THEN HMONTH := '0' || TO_CHAR(H_MONTH); ELSE HMONTH := TO_CHAR(H_MONTH); END IF; Return (HDAY || '-' || MONTH_NAME || '-' || TO_CHAR(H_YEAR)); END Georgian2Hijri;
 0 
FUNCTION Georgian2Hijri(G_DATE Date) RETURN Varchar2 IS
 1 
  H_DAY      NUMBER(2):=0;
 2 
  HDAY       VARCHAR2(2);
 3 
  H_MONTH    NUMBER(2):=1;
 4 
  HMONTH     VARCHAR2(2);
 5 
  H_YEAR     NUMBER(4):=1;
 6 
  FGDATE     DATE;
 7 
  I_LOOP     NUMBER;
 8 
  HY         NUMBER;
 9 
  MONTH_NAME VARCHAR2(40);
 10 
BEGIN
 11 
  FGDATE := TO_DATE('14-07-0622','DD-MM-YYYY');
 12 
  I_LOOP := G_DATE - FGDATE;
 13 
  LOOP
 14 
    IF I_LOOP<355 THEN
 15 
      EXIT;
 16 
    END IF;
 17 
    HY := TRUNC( H_YEAR / 30 ) * 30;
 18 
    IF (H_YEAR - HY) IN (2,5,7,10,13,16,18,21,24,26,29) THEN
 19 
      H_YEAR := H_YEAR + 1;
 20 
      I_LOOP := I_LOOP - 355;
 21 
    ELSE
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      I_LOOP := I_LOOP - 354;
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      H_YEAR := H_YEAR + 1;
 24 
    END IF;
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  END LOOP;
 26 
  FOR I IN 1..I_LOOP LOOP
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    H_DAY := H_DAY + 1;
 28 
    IF (H_MONTH=1 OR H_MONTH=3 OR H_MONTH=5 OR H_MONTH=7 OR H_MONTH=9 OR H_MONTH=11) AND H_DAY>30 THEN
 29 
      H_MONTH := H_MONTH + 1;
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      H_DAY   := 1;
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    END IF;
 32 
    IF (H_MONTH=2 OR H_MONTH=4 OR H_MONTH=6 OR H_MONTH=8 OR H_MONTH=10)AND H_DAY>29 THEN
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      H_MONTH := H_MONTH + 1;
 34 
      H_DAY   := 1;
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    END IF;
 36 
    HY := TRUNC( H_YEAR / 30 ) * 30;
 37 
    IF (H_YEAR - HY) IN (2,5,7,10,13,16,18,21,24,26,29) THEN
 38 
      IF H_MONTH=12 AND H_DAY>30 THEN
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        H_MONTH := H_MONTH + 1;
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        H_DAY   := 1;
 41 
        IF H_MONTH>12 THEN
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          H_YEAR  := H_YEAR + 1;
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          H_MONTH := 1;
 44 
        END IF;
 45 
      END IF;
 46 
    ELSE
 47 
      IF H_MONTH=12 AND H_DAY>29 THEN
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        H_MONTH := H_MONTH + 1;
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        H_DAY   := 1;
 50 
        IF H_MONTH>12 THEN
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          H_YEAR  := H_YEAR + 1;
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          H_MONTH := 1;
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        END IF;
 54 
      END IF;
 55 
    END IF;
 56 
  END LOOP;
 57 
  SELECT DECODE(H_MONTH
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         ,1,'محرم'
 59 
         ,2,'صفر'
 60 
         ,3,'ربيع الأول'
 61 
         ,4,'ربيع الثاني
 62 
         ,5,'جمادى الأولى
 63 
         ,6,'جمادة الآخرة
 64 
         ,7,'رجب'
 65 
         ,8,'شعبان'
 66 
         ,9,'رمضان'
 67 
         ,10,'شوال'
 68 
         ,11,'ذي القعدة'
 69 
         ,12,ذي الحجة',NULL)
 70 
    INTO MONTH_NAME
 71 
    FROM DUAL;
 72 
  IF H_DAY<10 THEN
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    HDAY := '0' || TO_CHAR(H_DAY);
 74 
  ELSE
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    HDAY := TO_CHAR(H_DAY);
 76 
  END IF;
 77 
  IF H_MONTH<10 THEN
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    HMONTH := '0' || TO_CHAR(H_MONTH);
 79 
  ELSE
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    HMONTH := TO_CHAR(H_MONTH);
 81 
  END IF;
 82 
  Return (HDAY || '-' || MONTH_NAME || '-' || TO_CHAR(H_YEAR));
 83 
END Georgian2Hijri;
Key Components
1. Input/Output
- Takes Gregorian date (`G_DATE`)
- Returns Hijri date as string (e.g., 01-ربيع الأول-1446)

2. Base Reference
Uses the Hijri epoch: 14 July 622 AD (`FGDATE`)

3. Variables
- `H_DAY/H_MONTH/H_YEAR`: Track Hijri date components
- `I_LOOP`: Days between input date and epoch
- `HY`: Leap year calculation helper

Conversion Process
1. Year Calculation
- Subtracts epoch date from input date to get total days (`I_LOOP`)
- Uses 30-year lunar cycles (11 leap years per cycle):
- Regular years = 354 days
- Leap years = 355 days
- Adjusts year count based on remaining days

2. Day/Month Calculation
- Processes remaining days using Hijri month rules:
- Odd months = 30 days (Muharram, Safar, etc.)
- Even months = 29 days
- Dhu al-Hijjah (12th month) varies:
- 30 days in leap years
- 29 days otherwise

3. Month Names
Uses Arabic month names via `DECODE`:

1 → محرم (Muharram)
3 → ريع الأول (Rabi' al-Awwal)
9 → رمضان (Ramadan)
12 → ذو الحجة (Dhu al-Hijjah)


4. Formatting
- Adds leading zeros to single-digit days/months
- Returns final string in DD-MonthName-YYYY format

Key Characteristics
- Algorithm Type: Approximate astronomical calculation
- Accuracy: Follows tabular Islamic calendar rules
- Limitations:
- Doesn't account for lunar sightings
- Uses fixed leap year pattern
- Month names require Unicode support

This implementation provides a practical conversion method for applications needing approximate Hijri dates without real-time moon observations.