Snipped from the Calibre Help page:Search & sort
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Dates
The syntax for searching for dates is:
pubdate:>2000-1 Will find all books published after Jan, 2000
date:<=2000-1-3 Will find all books added to calibre before 3 Jan, 2000
pubdate:=2009 Will find all books published in 2009
If the date is ambiguous then the current locale is used for date comparison. For example, in an mm/dd/yyyy locale 2/1/2009 is interpreted as 1 Feb 2009. In a dd/mm/yyyy locale it is interpreted as 2 Jan 2009. Some special date strings are available. The string today translates to today’s date, whatever it is. The strings yesterday and thismonth (or the translated equivalent in the current language) also work. In addition, the string daysago (also translated) can be used to compare to a date some number of days ago. For example:
date:>10daysago
date:<=45daysago
To avoid potential problems with translated strings when using a non-English version of calibre, the strings _today, _yesterday, _thismonth, and _daysago are always available. They are not translated.
Searching dates and numeric values with relational comparisons
Dates and numeric fields support the relational operators = (equals), > (greater than), >= (greater than or equal to), < (less than), <= (less than or equal to), and != (not equal to). Rating fields are considered to be numeric. For example, the search rating:>=3 will find all books rated 3 or higher.
You can search for books that have a format of a certain size like this:
size:>1.1M will find books with a format larger than 1.1MB
size:<=1K will find books with a format smaller than or equal to 1KB
You can search for the number of items in multiple-valued fields such as tags using the character # then using the same syntax as numeric fields. For example, to find all books with more than 4 tags use tags:#>4. To find all books with exactly 10 tags use tags:#=10.
These can be used in a calculated from others field (I am not a expert at that
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