Query With STR_TO_DATE() Giving 000-00-00 - mysql

Question

Here's my MySQL query:
SELECT YEARWEEK(paid) AS yweek,
STR_TO_DATE(YEARWEEK(paid), '%X%V') AS date,
COUNT(*) AS cnt
FROM members
WHERE YEARWEEK(paid) >= YEARWEEK(curdate()) - 52
GROUP BY yweek
Here is the result:
yweek date cnt
201429 0000-00-00 201
201430 0000-00-00 435
201431 0000-00-00 333
201432 0000-00-00 470
201433 0000-00-00 534
The yweek column and cnt column are fine, but the date column is always 0000-00-00. The paid column in the members table is of the format (PHP) date("Y-m-d H:i:s"), is of the column type TIMESTAMP, and here's an example: 2014-06-26 00:32:02.
I have tried replacing YEARWEEK(paid) with CAST(YEARWEEK(paid) AS CHAR(7)), but that changes nothing.
Does the fact that I'm using a TIMESTAMP cause STR_TO_DATE() to give all zeros? I want to have the first date of the week along with cnt, the number of registrations in that week.

Answer 1

Problem is: you cannot get a date from a yearweek: there's 7 options, which one do you want?
mysql> SELECT STR_TO_DATE('201429', '%X%V');
+-------------------------------+
| STR_TO_DATE('201429', '%X%V') |
+-------------------------------+
| 0000-00-00 |
+-------------------------------+
1 row in set (0.00 sec)
If we add a 'day of the week' (%w) to it, it magically begins to worK:
mysql> SELECT STR_TO_DATE('2014290', '%X%V%w');
+----------------------------------+
| STR_TO_DATE('2014290', '%X%V%w') |
+----------------------------------+
| 2014-07-20 |
+----------------------------------+
1 row in set (0.00 sec)
But: this means you have to choose the day of the week you want statically, because the original date is no longer in a yearweek.
Of course, in this case, you might as well have done this:
SELECT
YEARWEEK(paid) AS yweek,
DATE(paid) AS date,
COUNT(*) AS cnt
....
... but I assumed this was just an illustration of the problem getting a date of a yearweek string. If not, then this second solution will just work for you.