The FIND_IN_SET function looks for the string str in the string list strlist and returns a position of str if it exists. A string list is a string composed of substrings separated by a comma (,).
If str is not in strlist or strlist is an empty string, 0 is returned. If either argument is NULL, NULL is returned. This function does not work properly if str contains a comma (,).
FIND_IN_SET(str, strlist)
SELECT FIND_IN_SET('b','a,b,c,d');
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