As per my knowledge please find the explanation below:
1.Left join is written to forcefully link with the product_temp table with the date and month, i don't find special meaning in the that probably if a date field in product_temp table would have add a meaning.
2.date(monthstart(Date),'MMM YYYY') as Month > this syntax will Returns a value corresponding to a timestamp with the first millisecond of the first date of the month containing date. The default output format will be the DateFormat set in the script.
eg:monthstart ( '2001-10-19' ) returns '2001-10-01' with an underlying numeric value corresponding to '2001-10-01 00:00:00.000'
3.AutoNumber> Returns a unique integer value for each distinct evaluated value of expression encountered during the script execution. This function can be used e.g. for creating a compact memory representation of a complex key.
** urs is not auto number its autogenerate.
autogenerate is used if data should be automatically generated by QlikView.
size ::= number
Number is an integer indicating the number of records to be generated. The field list must not contain expressions which require data from a database. Only constants and parameter-free functions (e.g. rand(), recno()) are allowed in the expressions.
4. Random Function>Returns a random number between 0 and 1.
5.Mod>Mathematical modula function. Both parameters must have integer values. x2 must be greater than 0. The result is the non-negative remainder of an integer division.
Eg: mod( 7,2 ) returns 1
mod( 7.5,2 ) returns NULL
mod( 9,3 ) returns 0
mod( -4,3 ) returns 2
In your case they are posing a condition that the value mod(recno(),2) should not be equal to the value mod(round(rand()*1000),3) (<> means not equal)
