How to get the first and last days of a given month

problem ：

I wish to rewrite a mysql query which use month() and year() functions to display all the posts from a certain month which goes to my function as a 'Ymd' parameter format, but I don't know how can I get the last day of the given month date. I want to rewrite one mysql Inquire about , It USES month（） and year（） Function to display all posts in a month , These posts serve as 'Ymd' Parameter format goes to my function , But I don't know how to get the last day of a given month .

$query_date = '2010-02-04';list($y, $m, $d) = explode('-', $query_date);$first_day = $y . '-' . $m . '-01';

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Solution ：

Reference resources ： https://stackoom.com/en/question/Ve0A