Documentation bug. See code:

// Returns a week index conforming to the MySQL WEEK() function.  Note

// that modeflags is not the MySQL mode - it is a bitmask of the abvoe

// 3 flags.  The utility function convert_mysql_mode_to_modeflags should

// be applied to the MySQL mode before calling this function (or the

// flags may be used directly).  The optional argument is for callers

// that need to know the year that the week actually corresponds to -

// see MySQL documentation for how the year returned can be different

// than the year of the input date

From PostGreSQL

The number of the week of the year that the day is in. By definition (ISO 8601), the first week of a year contains January 4 of that year. (The ISO-8601 week starts on Monday.) In other words, the first Thursday of a year is in week 1 of that year. (for timestamp values only)

Because of this, it is possible for early January dates to be part of the 52nd or 53rd week of the previous year. For example, 2005-01-01 is part of the 53rd week of year 2004, and 2006-01-01 is part of the 52nd week of year 2005.

From Oracle

WEEK (1 - 53) Returns the rank of the week in the year, where the first week starts on the first day of the year.

From these, I conclude that EXTRACT(WEEK..) should return a 1 based number.

I was comparing the MariaDB server and assumed MariaDB is correct. Does that mean a bug in the server? or we are just going with different standard.

I even compared results for days in May and they are off by 1.

Seems it's a bit more complicated. According to https://mariadb.com/kb/en/library/week/, this is configurable via system variable default-week-format. We don't currently bring system variables down to functions. We may want to consider doing that.

There are two separate problems here:

1. We need to document what is in my first comment (this bug)
2. We should push down MariaDB's session variables into ExeMgr and PrimProc so that we can use the variable for this, then the behaviour will be the same as MariaDB. This should be a feature request. I'll file this shortly.

Actually this isn't a documentation bug. For WEEK() the plugin takes the MariaDB system variable and makes this a parameter. It doesn't do this for EXTRACT() with WEEK.

Item is out of date. Closing due to inactivity. If you feel this was done in error please open a new ticket.