Question

I want to run a SELECT query on table which picks up the date stored in the year_end field and automatically treats it as being that occurrence of the date in the last 12 months.

I.e.: today is May 14th so:

If I have 2012-01-01 then I want that unchanged

If I have 2010-05-05 then I want 2012-05-05

If I have 2012-10-10 then I want 2011-10-10

Any ideas on the SELECT I need please?

Answer 1

Here is what you need:

select
concat(yr,'-',if(leapyear=0,if(right(dt,5)='02-29','03-01',
right(@mydate,5)),right(@mydate,5))) dttm
from
(
    select concat(if(my_md > md,yr -1,yr),'-',my_md) dt,yr,my_md,
    IF(MOD(yr,4)>0,0,IF(MOD(yr,100),1,(MOD(yr,400)=0))) leapyear FROM
    (select substr(date(@mydate),6) my_md) AA,
    (select substr(date(now()),6) md,year(now()) yr) BB
) A;

Here are the three dates you chose as examples + 2 leap year dates

set @mydate = '2012-01-01';
set @mydate = '2010-05-05';
set @mydate = '2012-10-10';
set @mydate = '2008-02-29';
set @mydate = '2012-02-29';

Here they are executed

mysql> set @mydate = ‘2012-01-01’;
Query OK, 0 rows affected (0.00 sec)

mysql> select
    -> concat(yr,'-',if(leapyear=0,if(right(dt,5)='02-29','03-01',right(@mydate,5)),right(@mydate,5))) dttm
    -> from
    -> (
    ->     select concat(if(my_md > md,yr -1,yr),'-',my_md) dt,yr,my_md,
    ->     IF(MOD(yr,4)>0,0,IF(MOD(yr,100),1,(MOD(yr,400)=0))) leapyear FROM
    ->     (select substr(date(@mydate),6) my_md) AA,
    ->     (select substr(date(now()),6) md,year(now()) yr) BB
    -> ) A;
+------------+
| dttm       |
+------------+
| 2012-01-01 |
+------------+
1 row in set (0.00 sec)

mysql> set @mydate = '2010-05-05';
Query OK, 0 rows affected (0.00 sec)

mysql> select
    -> concat(yr,'-',if(leapyear=0,if(right(dt,5)='02-29','03-01',right(@mydate,5)),right(@mydate,5))) dttm
    -> from
    -> (
    ->     select concat(if(my_md > md,yr -1,yr),'-',my_md) dt,yr,my_md,
    ->     IF(MOD(yr,4)>0,0,IF(MOD(yr,100),1,(MOD(yr,400)=0))) leapyear FROM
    ->     (select substr(date(@mydate),6) my_md) AA,
    ->     (select substr(date(now()),6) md,year(now()) yr) BB
    -> ) A;
+------------+
| dttm       |
+------------+
| 2012-05-05 |
+------------+
1 row in set (0.00 sec)

mysql> set @mydate = '2012-10-10';
Query OK, 0 rows affected (0.00 sec)

mysql> select
    -> concat(yr,'-',if(leapyear=0,if(right(dt,5)='02-29','03-01',right(@mydate,5)),right(@mydate,5))) dttm
    -> from
    -> (
    ->     select concat(if(my_md > md,yr -1,yr),'-',my_md) dt,yr,my_md,
    ->     IF(MOD(yr,4)>0,0,IF(MOD(yr,100),1,(MOD(yr,400)=0))) leapyear FROM
    ->     (select substr(date(@mydate),6) my_md) AA,
    ->     (select substr(date(now()),6) md,year(now()) yr) BB
    -> ) A;
+------------+
| dttm       |
+------------+
| 2012-10-10 |
+------------+
1 row in set (0.00 sec)

mysql> set @mydate = '2008-02-29';
Query OK, 0 rows affected (0.00 sec)

mysql> select
    -> concat(yr,'-',if(leapyear=0,if(right(dt,5)='02-29','03-01',right(@mydate,5)),right(@mydate,5))) dttm
    -> from
    -> (
    ->     select concat(if(my_md > md,yr -1,yr),'-',my_md) dt,yr,my_md,
    ->     IF(MOD(yr,4)>0,0,IF(MOD(yr,100),1,(MOD(yr,400)=0))) leapyear FROM
    ->     (select substr(date(@mydate),6) my_md) AA,
    ->     (select substr(date(now()),6) md,year(now()) yr) BB
    -> ) A;
+------------+
| dttm       |
+------------+
| 2012-02-29 |
+------------+
1 row in set (0.00 sec)

mysql> set @mydate = '2012-02-29';
Query OK, 0 rows affected (0.00 sec)

mysql> select
    -> concat(yr,'-',if(leapyear=0,if(right(dt,5)='02-29','03-01',right(@mydate,5)),right(@mydate,5))) dttm
    -> from
    -> (
    ->     select concat(if(my_md > md,yr -1,yr),'-',my_md) dt,yr,my_md,
    ->     IF(MOD(yr,4)>0,0,IF(MOD(yr,100),1,(MOD(yr,400)=0))) leapyear FROM
    ->     (select substr(date(@mydate),6) my_md) AA,
    ->     (select substr(date(now()),6) md,year(now()) yr) BB
    -> ) A;
+------------+
| dttm       |
+------------+
| 2012-02-29 |
+------------+
1 row in set (0.00 sec)

mysql>

Give it a Try !!!