Mysql – How to get dates that wrap around new year from non-datetime columns

database-designdateMySQL

I have a table in my MySQL database that stores daily data (an entry for each day of the year), but does not use a DATETIME column for this. This is because the data is the same for every year (it's climatology data, so the "normal" high temperature for Jan 7, 2015 is the same as for Jan 7, 2016 and so on). I have three fields that represent the day this data is valid for, so my table looks like:

month, day_of_month, day_of_year, value
1      1             1            23
1      2             2            22.95
...
12     31            365          23.12

Say I then want to get the values from this table from a certain date, like 01 Dec 2015 to 60 days from then, which would be 30 Jan 2016. Is there a way to get back the date and value for all of those days, working okay across the new year? Ideally I'd love results that flow like:

valid_date, value
...
2015-12-31  23.12
2016-01-01  23
2016-01-02  22.95
...

(hopefully you get the idea).

If you can think of a better way to store this static daily data so that I can achieve the above goal, I'm open to that as well! Thanks for your help!

Best Answer

You can use MAKEDATE(), it makes the day_of_year to a date.

Test:

mysql> SELECT * FROM cli_table;
+-------+--------------+-------------+-------+
| month | day_of_month | day_of_year | value |
+-------+--------------+-------------+-------+
|     1 |            1 |           1 | 23.00 |
|     1 |            2 |           2 | 22.95 |
|    12 |           31 |         365 | 23.12 |
+-------+--------------+-------------+-------+
3 rows in set (0.00 sec)

mysql> SELECT 
    -> MAKEDATE(YEAR(CURDATE()),day_of_year) AS Date,
    ->     value AS DayValue
    -> FROM test.cli_table;
+------------+----------+
| Date       | DayValue |
+------------+----------+
| 2015-01-01 |    23.00 |
| 2015-01-02 |    22.95 |
| 2015-12-31 |    23.12 |
+------------+----------+
3 rows in set (0.00 sec)

mysql>

You can try it in this Fiddle.

EDIT:

According of what you want, you can make it with pure SQL:

mysql> SELECT * FROM test.cli_table;
+-------+--------------+-------------+-------+
| month | day_of_month | day_of_year | value |
+-------+--------------+-------------+-------+
|     1 |            1 |           1 |  5.00 |
|     1 |            2 |           2 |  6.00 |
|     1 |            3 |           3 |  7.00 |
|    12 |           25 |         359 | 23.00 |
|    12 |           26 |         360 | 22.95 |
|    12 |           27 |         361 |  1.00 |
|    12 |           28 |         362 |  2.00 |
|    12 |           29 |         363 |  3.00 |
|    12 |           30 |         364 |  4.00 |
|    12 |           31 |         365 | 23.12 |
+-------+--------------+-------------+-------+
10 rows in set (0.00 sec)

mysql> SELECT 
    -> v.selected_date,
    -> v.dayyear,
    -> c.value AS DayValue,
    -> c.day_of_year 
    -> FROM test.cli_table AS c
    -> JOIN (SELECT 
    -> adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) AS selected_date,
    -> DAYOFYEAR(adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i)) AS dayyear
    -> FROM 
    -> (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0,
    -> (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1,
    -> (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2,
    -> (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3,
    -> (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) AS v
    -> ON (v.selected_date between '2015-12-25' AND '2016-01-03'
    -> AND v.dayyear=c.day_of_year);
+---------------+---------+----------+-------------+
| selected_date | dayyear | DayValue | day_of_year |
+---------------+---------+----------+-------------+
| 2015-12-25    |     359 |    23.00 |         359 |
| 2015-12-26    |     360 |    22.95 |         360 |
| 2015-12-27    |     361 |     1.00 |         361 |
| 2015-12-28    |     362 |     2.00 |         362 |
| 2015-12-29    |     363 |     3.00 |         363 |
| 2015-12-30    |     364 |     4.00 |         364 |
| 2015-12-31    |     365 |    23.12 |         365 |
| 2016-01-01    |       1 |     5.00 |           1 |
| 2016-01-02    |       2 |     6.00 |           2 |
| 2016-01-03    |       3 |     7.00 |           3 |
+---------------+---------+----------+-------------+
10 rows in set (0.00 sec)

mysql>

Query Meaning:

SELECT 
    v.selected_date,
    v.dayyear,
    c.value AS DayValue,
    c.day_of_year 
FROM test.cli_table AS c
--- > This JOIN is generating all the dates between the selected_dates ('2015-12-25' AND '2016-01-03')
JOIN (SELECT 
        adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) AS selected_date,
        DAYOFYEAR(adddate('1970-01-01',t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i)) AS dayyear
      FROM 
     (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0,
     (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1,
     (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2,
     (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3,
     (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) AS v
--- > Here I'm matching every dayyear of the generated dates with the cli_table.day_of_year.
ON (v.selected_date between '2015-12-25' AND '2016-01-03'
    AND v.dayyear=c.day_of_year);
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