Contents

• pg_ethiopian_calendar
  • Description
  • Installation
    • From PGXN
    • From Source
    • Create Extension
  • Quick Start
  • Functions
    • to_ethiopian_date(timestamp) → text
    • from_ethiopian_date(text) → timestamp
    • to_ethiopian_timestamp(timestamp) → timestamp
    • to_ethiopian_datetime(timestamp) → timestamptz
    • current_ethiopian_date() → text
  • Function Aliases
  • Usage Examples
    • Generated Columns
    • Default Values
    • Indexing
  • Ethiopian Calendar Overview
  • Compatibility
  • Testing
  • Author
  • License
  • Links
  • References

pg_ethiopian_calendar

A PostgreSQL extension for converting between Gregorian and Ethiopian calendar dates.

Description

The Ethiopian calendar (Ge'ez calendar) is a solar calendar with 13 months used in Ethiopia and Eritrea. This extension provides functions to convert dates between Gregorian and Ethiopian calendars using academically verified algorithms from "Calendrical Calculations" by Dershowitz & Reingold.

Key Features:

• Bidirectional conversion (Gregorian ↔ Ethiopian)
• IMMUTABLE functions for use in indexes and generated columns
• Time-preserving conversions
• NULL-safe operations

Installation

From PGXN

pgxn install pg_ethiopian_calendar

From Source

git clone https://github.com/HuluWZ/pg-ethiopian-calendar.git
cd pg-ethiopian-calendar
make
sudo make install

Create Extension

CREATE EXTENSION pg_ethiopian_calendar;

Quick Start

-- Convert Gregorian to Ethiopian
SELECT to_ethiopian_date('2024-01-01'::timestamp);
-- Returns: '2016-04-23'

-- Convert Ethiopian to Gregorian  
SELECT from_ethiopian_date('2016-04-23');
-- Returns: '2024-01-01 00:00:00'

-- Get current Ethiopian date
SELECT current_ethiopian_date();
-- Returns: Current date in Ethiopian calendar

Functions

to_ethiopian_date(timestamp) → text

Converts a Gregorian timestamp to Ethiopian date string.

SELECT to_ethiopian_date('2024-01-01'::timestamp);
-- '2016-04-23'

from_ethiopian_date(text) → timestamp

Converts an Ethiopian date string to Gregorian timestamp.

SELECT from_ethiopian_date('2016-04-23');
-- '2024-01-01 00:00:00'

to_ethiopian_timestamp(timestamp) → timestamp

Converts Gregorian timestamp to Ethiopian timestamp (preserves time). Ideal for generated columns.

SELECT to_ethiopian_timestamp('2024-01-01 14:30:00'::timestamp);

to_ethiopian_datetime(timestamp) → timestamptz

Converts Gregorian timestamp to Ethiopian timestamp with time zone.

SELECT to_ethiopian_datetime('2024-01-01 14:30:00'::timestamp);

current_ethiopian_date() → text

Returns current date in Ethiopian calendar. (STABLE, not IMMUTABLE)

SELECT current_ethiopian_date();

Function Aliases

All functions have pg_ prefixed aliases following PostgreSQL naming conventions:

Function	Alias
to_ethiopian_date()	pg_ethiopian_to_date()
from_ethiopian_date()	pg_ethiopian_from_date()
to_ethiopian_timestamp()	pg_ethiopian_to_timestamp()
to_ethiopian_datetime()	pg_ethiopian_to_datetime()

Usage Examples

Generated Columns

CREATE TABLE orders (
    id SERIAL PRIMARY KEY,
    created_at TIMESTAMP DEFAULT NOW(),
    created_at_ethiopian TIMESTAMP GENERATED ALWAYS AS 
        (to_ethiopian_timestamp(created_at)) STORED
);

INSERT INTO orders DEFAULT VALUES;
SELECT * FROM orders;

Default Values

CREATE TABLE events (
    id SERIAL PRIMARY KEY,
    event_date TEXT DEFAULT current_ethiopian_date()
);

Indexing

CREATE INDEX idx_orders_ethiopian 
ON orders (to_ethiopian_date(created_at));

Ethiopian Calendar Overview

Property	Value
Months	13 (12 × 30 days + 1 × 5-6 days)
Leap Year	Every 4 years (year % 4 == 3)
New Year	September 11-12 (Gregorian)
Year Offset	~7-8 years behind Gregorian

Month Names: Meskerem, Tikimt, Hidar, Tahsas, Tir, Yekatit, Megabit, Miazia, Ginbot, Sene, Hamle, Nehase, Pagumē

Compatibility

• PostgreSQL 11, 12, 13, 14, 15, 16, 17

Testing

# Using Docker
make docker-test

# Manual
psql -d mydb -f test/tests/ethiopian_calendar_tests.sql

Author

Hulunlante Worku — hulunlante.w@gmail.com

License

Released under the PostgreSQL License.

Links

• PGXN: https://pgxn.org/dist/pg_ethiopian_calendar/
• GitHub: https://github.com/HuluWZ/pg-ethiopian-calendar
• Issues: https://github.com/HuluWZ/pg-ethiopian-calendar/issues

References

• Dershowitz, N. & Reingold, E.M. (2008). Calendrical Calculations (3rd ed.). Cambridge University Press.