April 16 2018

MySQL week() function not correct display

Tagged Under :

MySQL
I am try gather some statistics from a database and it need group by week numbers. and the results return unexpected.
SELECT create_date, WEEK(create_date) as week FROM `ttable` 
+---------------------+-------------+
| craete_date         | week        |
+---------------------+-------------+
| 2018-01-02 00:00:00 |           0 | 
| 2018-04-10 00:00:00 |          14 | 
| 2018-03-13 00:00:00 |          10 | 
| 2018-03-30 00:00:00 |          12 | 
+---------------------+-------------+
From the above you will found that the week number was wrong. and MySQL counts the first days of the year that do not belong week 1 as week 0.

This is because MySQL default week() function caused the issue. because in MySQL the first day of week is Sunday and it range was 0 to 53 weeks. And you need change the MySQL mode with the below table.
+--------------------------------------------------------------------+
| Mode | First day of week | Range | Week 1 is the first week        |
|------+-------------------+-------+---------------------------------|
| 0    | Sunday            | 0-53  | with a Sunday in this year      |
|------+-------------------+-------+---------------------------------|
| 1    | Monday            | 0-53  | with more than 3 days this year |
|------+-------------------+-------+---------------------------------|
| 2    | Sunday            | 1-53  | with a Sunday in this year      |
|------+-------------------+-------+---------------------------------|
| 3    | Monday            | 1-53  | with more than 3 days this year |
|------+-------------------+-------+---------------------------------|
| 4    | Sunday            | 0-53  | with more than 3 days this year |
|------+-------------------+-------+---------------------------------|
| 5    | Monday            | 0-53  | with a Monday in this year      |
|------+-------------------+-------+---------------------------------|
| 6    | Sunday            | 1-53  | with more than 3 days this year |
|------+-------------------+-------+---------------------------------|
| 7    | Monday            | 1-53  | with a Monday in this year      |
+--------------------------------------------------------------------+
What I needed was mode 3 of the week() function. and we try run the query with the mode and see what the results.
SELECT create_date, WEEK(create_date, 3) as week FROM `ttable` 
+---------------------+-------------+
| craete_date         | week        |
+---------------------+-------------+
| 2018-01-02 00:00:00 |           1 | 
| 2018-04-10 00:00:00 |          15 | 
| 2018-03-13 00:00:00 |          11 | 
| 2018-03-30 00:00:00 |          13 | 
+---------------------+-------------+
Yes, above is show me the correct results

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