Finds the date for Easter (Western) given a year.
Sample usage: SELECT easter(YEAR(NOW()));

DELIMITER //
CREATE FUNCTION easter(inYear YEAR) RETURNS DATE DETERMINISTIC
BEGIN
    DECLARE a, b, c, d, e, k, m, n, p, q INT;

    DECLARE easter DATE;

    SET k = FLOOR(inYear / 100);
    SET a = MOD(inYear, 19);
    SET b = MOD(inYear, 4);
    SET c = MOD(inYear, 7);
    SET q = FLOOR(k / 4);
    SET p = FLOOR((13 + 8 * k) / 25);
    SET m = MOD((15-p+k-q), 30);
    SET d = MOD((19 * a + m), 30);
    SET n = MOD((4+k-q), 7);
    SET e = MOD((2*b+4*c+6*d+n), 7);

    SET easter = CASE
        WHEN d + e <= 9 THEN CONCAT_WS('-', inYear, '03', 22 + d + e)
        WHEN d = 29 AND e = 6 THEN CONCAT_WS('-', inYear, '04-19')
        WHEN d = 28 AND e = 6 AND a > 10 THEN CONCAT_WS('-', inYear, '04-18')
        ELSE CONCAT_WS('-', inYear, '04', LPAD(d + e - 9, 2, 0))
    END;

    RETURN easter;
END
//
DELIMITER ;