mySQL - Generate Additional Lines Between Dates [duplicate] - mysql

Question

This question already has answers here:
MySQL how to fill missing dates in range?
(6 answers)
Closed 6 years ago.
I have a table like the below.
id month duration
001 1/1/16 3
002 3/1/16 4
003 12/1/15 2
I would like to add a new row to the table for every month after the month shown for the number specified minus 1, e.g. below:
id month duration
001 1/1/16 3
001 2/1/16 3
001 3/1/16 3
002 3/1/16 4
002 4/1/16 4
002 5/1/16 4
002 6/1/16 4
003 12/1/15 2
003 1/1/16 2
And so on, while duplicating the values in any column not shown.
I have done this in R, where I first populated 'short' data and then reshaped it to long, but after searching online, I still have no idea how to do this in mySQL. Thanks in advance for your help!

Answer 1

If you could automatically generate rows in MySQL that would be pretty easy; except that you can't. Still, you could use the technique described here to generate some rows and then use a JOIN to get the data you need:
-- Create a VIEW with 16 dummy rows
CREATE OR REPLACE VIEW generator_16
AS SELECT 0 n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL
SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL
SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL
SELECT 9 UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL
SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14 UNION ALL
SELECT 15;
Having this generator, your query becomes:
SELECT id, date_add(month, INTERVAL n MONTH), duration
FROM tbl
INNER JOIN generator_16 ON n < duration
ORDER BY id, month
I assumed your table structure is the following:
CREATE TABLE tbl(id varchar(10), month date, duration int);
INSERT INTO tbl VALUES('001', '2016-01-01', 3);
INSERT INTO tbl VALUES('002', '2016-03-01', 4);
INSERT INTO tbl VALUES('003', '2015-12-01', 2);

Answer 2

Issues of data display are generally best resolved in the presentation layer (e.g. a simple PHP loop), but just for fun...
DROP TABLE IF EXISTS my_table;
CREATE TABLE my_table
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,dt DATE NOT NULL
,duration INT NOT NULL
);
INSERT INTO my_table VALUES
(1,'2016-01-01',3),
(2,'2016-03-01',4),
(3,'2015-12-01',2);
SELECT * FROM my_table;
+----+------------+----------+
| id | dt | duration |
+----+------------+----------+
| 1 | 2016-01-01 | 3 |
| 2 | 2016-03-01 | 4 |
| 3 | 2015-12-01 | 2 |
+----+------------+----------+
SELECT * FROM ints;
+---+
| i |
+---+
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 6 |
| 7 |
| 8 |
| 9 |
+---+
SELECT x.id,x.dt + INTERVAL y.i MONTH,x.duration FROM my_table x JOIN ints y ON y.i < x.duration;
+----+---------------------------+----------+
| id | x.dt + INTERVAL y.i MONTH | duration |
+----+---------------------------+----------+
| 1 | 2016-01-01 | 3 |
| 1 | 2016-02-01 | 3 |
| 1 | 2016-03-01 | 3 |
| 2 | 2016-03-01 | 4 |
| 2 | 2016-04-01 | 4 |
| 2 | 2016-05-01 | 4 |
| 2 | 2016-06-01 | 4 |
| 3 | 2015-12-01 | 2 |
| 3 | 2016-01-01 | 2 |
+----+---------------------------+----------+