select dates on this weekday in the past - mysql

Question

I have a list of dates ("start", datetime) and I would like to select all dates where :
today = start + 1 WEEK or
today = start + 2 WEEK or
today = start + 3 WEEK or
today = start + 4 WEEK or
today = start + 5 WEEK or
today = start + 6 WEEK
Maximum is start + 6 weeks.
Any idea ?

Answer 1

setup
create table example
(
id integer primary key not null auto_increment,
start datetime not null
);
insert into example ( start )
values
( date_sub(current_date, interval 1 week) ),
( date_sub(current_date, interval 2 week) ),
( date_sub(current_date, interval 3 week) ),
( date_sub(current_date, interval 4 week) ),
( date_sub(current_date, interval 5 week) ),
( date_sub(current_date, interval 6 week) ),
( date_sub(current_date, interval 6 week) ),
( date_sub(current_date, interval 4 week) ),
( date_sub(current_date, interval 9 week) ),
( date_sub(current_date, interval 12 week) )
;
query
select id, start
from example
where
date(start) in
(
date_sub(current_date, interval 1 week) ,
date_sub(current_date, interval 2 week) ,
date_sub(current_date, interval 3 week) ,
date_sub(current_date, interval 4 week) ,
date_sub(current_date, interval 5 week) ,
date_sub(current_date, interval 6 week)
)
;
output
+----+-----------------------------+
| id | start |
+----+-----------------------------+
| 1 | September, 16 2015 00:00:00 |
| 2 | September, 09 2015 00:00:00 |
| 3 | September, 02 2015 00:00:00 |
| 4 | August, 26 2015 00:00:00 |
| 5 | August, 19 2015 00:00:00 |
| 6 | August, 12 2015 00:00:00 |
| 7 | August, 12 2015 00:00:00 |
| 8 | August, 26 2015 00:00:00 |
+----+-----------------------------+
sqlfiddle

Answer 2

I assume you want a WHERE filter to capture all rows containing start DATETIMEs on this weekday one week ago, and two ... six weeks ago. That's the effect of the logic in your question:
today = start + 1 WEEK or today = start + 2 WEEK or ...
means the same thing as
start = today - 1 WEEK etc.
The thing is, you are using DATETIME values for start. They're not guaranteed to be start = CURDATE() because they may not be at midnight.
So, you need to use the DATE() function to reduce them to midnight values before comparing them. Something like this will work.
WHERE DATE(start) IN (
CURDATE() - INTERVAL 6 WEEK, CURDATE() - INTERVAL 5 WEEK, CURDATE() - INTERVAL 4 WEEK,
CURDATE() - INTERVAL 3 WEEK, CURDATE() - INTERVAL 2 WEEK, CURDATE() - INTERVAL 1 WEEK)
You could also do this -- it picks out all records six weeks old or newer, but not the ones in the most recent week, then picks the ones on today's weekday.
WHERE start >= CURDATE() - INTERVAL 6 WEEK
AND start < CURDATE() - 6 DAY
AND WEEKDAY(CURDATE()) = WEEKDAY(start)
This second formulation will be more efficient if you have a great deal of old data in your table and you have an index on your start column: the first two where clauses are sargeable.
Pro tip: When specifying this kind of date filter, the more effort you spend making your specification exact before you write code, the faster you will finish your work. That's true even if you don't count debugging time.

Answer 3

Could you use between?
So...
today BETWEEN start AND start + INTERVAL 6 WEEK
Something like that?

Answer 4

Try To run this query in mysql,
use dbname;
create table adddate
(
id integer primary key not null auto_increment,
initial datetime not null
)auto_increment=100;
insert into adddate ( initial )
values( DATE_ADD(current_date, interval 1 week) ),
( DATE_ADD(current_date, interval 2 week) ),
( DATE_ADD(current_date, interval 3 week) ),
( DATE_ADD(current_date, interval 4 week) ),
( DATE_ADD(current_date, interval 5 week) ),
( DATE_ADD(current_date, interval 6 week) )
;
date_add is an SQLfunction it is used to do addition operations on date
The syntax is:-
DATE_ADD(date,INTERVAL expr type)
the type can be:-
MICROSECOND,
SECOND,
MINUTE,
HOUR,
DAY,
WEEK,
MONTH,
QUARTER,
YEAR,
SECOND_MICROSECOND,
MINUTE_MICROSECOND,
MINUTE_SECOND,
HOUR_MICROSECOND,
HOUR_SECOND,
HOUR_MINUTE,
DAY_MICROSECOND,
DAY_SECOND,
DAY_MINUTE,
DAY_HOUR,
YEAR_MONTH;