How to perform date calculations that ignore the year using SQL
Problem:
You want to select dates that have an anniversary within the next 14 days, but you want to do this by excluding the year.
Example Query:
SELECT * FROM events WHERE EXTRACT(month FROM "date") = 3 AND EXTRACT(day FROM "date") < EXTRACT(day FROM "date") + 14;
Challenge:
The above query doesn't work because it doesn't account for the wrap-around effect of months.
Solutions:
1. Advanced Version
This solution uses a custom SQL function and a multicolumn index for optimal performance.
CREATE OR REPLACE FUNCTION f_mmdd(date)
RETURNS int LANGUAGE sql IMMUTABLE PARALLEL SAFE STRICT AS
'SELECT EXTRACT(month FROM )::int * 100 + EXTRACT(day FROM )::int';
CREATE INDEX event_mmdd_event_date_idx ON event(f_mmdd(event_date), event_date);
SELECT *
FROM event e
WHERE f_mmdd(e.event_date) BETWEEN f_mmdd(current_date)
AND f_mmdd(current_date + 14);2. Table Function
This solution uses a PostgreSQL table function to handle the anniversary calculation.
CREATE OR REPLACE FUNCTION f_anniversary(_the_date date = current_date, _days int = 14)
RETURNS SETOF event
LANGUAGE plpgsql AS
$func$
DECLARE
d int := f_mmdd();
d1 int := f_mmdd( + - 1); -- fix off-by-1 from upper bound
BEGIN
IF d1 > d THEN
RETURN QUERY
SELECT *
FROM event e
WHERE f_mmdd(e.event_date) BETWEEN d AND d1
ORDER BY f_mmdd(e.event_date), e.event_date;
ELSE -- wrap around end of year
RETURN QUERY
SELECT *
FROM event e
WHERE f_mmdd(e.event_date) >= d OR
f_mmdd(e.event_date) <= d1
ORDER BY (f_mmdd(e.event_date) >= d) DESC, f_mmdd(e.event_date), event_date;
-- chronological across turn of the year
END IF;
END
$func$;
SELECT * FROM f_anniversary();The above is the detailed content of How to Calculate Dates Ignoring the Year in SQL?. For more information, please follow other related articles on the PHP Chinese website!
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