Informix - Date/Time Manipulation in where clause - informix

Question

See below query:
DROP TABLE IF EXISTS rd_rt_date_integer;
CREATE TABLE rd_rt_date_integer
(
run_date DATE NOT NULL,
run_time INTEGER NOT NULL
CHECK (run_time >= 0 AND run_time < 2400 AND MOD(run_time, 100) < 60),
PRIMARY KEY(run_date, run_time)
);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 0);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 100);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 200);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 300);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 400);
SELECT run_date, run_time,
EXTEND(run_date, YEAR TO MINUTE) +
MOD(run_time, 100) UNITS MINUTE +
(run_time / 100) UNITS HOUR AS run_date_time
FROM rd_rt_date_integer;
Question: How can we apply condition in where to clause to fetch data from certain time onwards
SELECT run_date, run_time,
EXTEND(run_date, YEAR TO MINUTE) +
MOD(run_time, 100) UNITS MINUTE +
(run_time / 100) UNITS HOUR AS run_date_time
FROM rd_rt_date_integer
where EXTEND(run_date, YEAR TO MINUTE) +
MOD(run_time, 100) UNITS MINUTE +
(run_time / 100) UNITS HOUR >='2017-05-22 02:00'
I just want to understand what is the best way to do manipulation in where clause itself where im concatenating run_date and run_time...

Answer 1

It would be simpler if you stored the time as an INTERVAL HOUR TO MINUTE.
Then you could simplify the first query by using:
DROP TABLE IF EXISTS rd_rt_date_integer;
CREATE TABLE rd_rt_date_integer
(
run_date DATE NOT NULL,
run_time INTERVAL HOUR TO MINUTE NOT NULL
CHECK (run_time >= INTERVAL(0:0) HOUR TO MINUTE AND run_time < INTERVAL(24:00) HOUR TO MINUTE),
PRIMARY KEY(run_date, run_time)
);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', '0:0');
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', '1:00');
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', '2:00');
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', '3:00');
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', '4:00');
SELECT run_date, run_time,
EXTEND(run_date, YEAR TO MINUTE) + run_time AS run_date_time
FROM rd_rt_date_integer;
However, you presumably have a reason for using the integer run_time, even though it makes time calculations hellish.
This code works — I recommend using the stored procedure:
DROP TABLE IF EXISTS rd_rt_date_integer;
CREATE TABLE rd_rt_date_integer
(
run_date DATE NOT NULL,
run_time INTEGER NOT NULL
CHECK (run_time >= 0 AND run_time < 2400 AND MOD(run_time, 100) < 60),
PRIMARY KEY(run_date, run_time)
);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 0);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 100);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 200);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 300);
INSERT INTO rd_rt_date_integer VALUES('2017-05-22', 400);
SELECT run_date, run_time,
EXTEND(run_date, YEAR TO MINUTE) +
MOD(run_time, 100) UNITS MINUTE +
(run_time / 100) UNITS HOUR AS run_date_time
FROM rd_rt_date_integer
WHERE EXTEND(run_date, YEAR TO MINUTE) +
MOD(run_time, 100) UNITS MINUTE +
(run_time / 100) UNITS HOUR >= DATETIME(2017-05-22 02:00) YEAR TO MINUTE
OR EXTEND(run_date, YEAR TO MINUTE) +
MOD(run_time, 100) UNITS MINUTE +
(run_time / 100) UNITS HOUR >= EXTEND('2017-05-22 02:00', YEAR TO MINUTE)
;
DROP FUNCTION IF EXISTS run_date_time;
CREATE FUNCTION run_date_time(rd DATE, rt INTEGER)
RETURNING DATETIME YEAR TO MINUTE;
DEFINE rv DATETIME YEAR TO MINUTE;
LET rv = EXTEND(rd, YEAR TO MINUTE) + MOD(rt, 100) UNITS MINUTE + (rt / 100) UNITS HOUR;
RETURN rv;
END FUNCTION;
SELECT run_date, run_time,
run_date_time(run_date, run_time) AS run_date_time
FROM rd_rt_date_integer
WHERE run_date_time(run_date, run_time) >= DATETIME(2017-05-22 02:00) YEAR TO MINUTE
OR run_date_time(run_date, run_time) >= EXTEND('2017-05-22 02:00', YEAR TO MINUTE)
OR run_date_time(run_date, run_time) >= run_date_time('2017-05-22', 200)
;
The OR conditions in the later SELECT statements show different nomenclatures for writing the condition. They're otherwise identical and only one of the conditions is needed; the others are superfluous.
If you simply stored the minutes since midnight in the run_time column, rather than encoding it as 100 * hours + minutes, then you could write expressions like:
DATETIME(2017-06-12 00:00) YEAR TO MINUTE + 245 UNITS MINUTE
That expression evaluates to 2017-06-12 04:05. You could easily arrange to update the table to this encoding. There are obvious variants of this, such as:
EXTEND(TODAY, YEAR TO MINUTE) + 245 UNITS MINUTE
EXTEND(run_date, YEAR TO MINUTE) + run_time UNITS MINUTE