Number of pairs in SQL


Suppose you're given the following table showing sock inventory. Each row represents an individual sock (with the same style/size), and the 'color' column denotes the sock's color. Given this information, write a SQL query to return the number of pairs (two socks with matching colors) that can be made from the inventory shown. Your result should be returned as a single integer number.

Table: color_sorting

sock_id color
1 red
2 blue
3 black
4 blue
5 red
6 black
7 red
8 white
9 red
10 blue
11 red
12 red

You can view/query the data in an interactive SQL fiddle here.


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