Comments - FIND_IN_SET
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if you wish to update a record and remove an element from a SET, you can't use UPDATE my_table SET my_col = my_col - 'element_to_remove' and you can't use UPDATE my_table SET my_col = my_col - FIND_IN_SET('element_to_remove',my_col)
Rather, you must use bit arithmetic this way: UPDATE my_table SET my_col = my_col - floor(pow(2,find_in_set('element_to_remove',my_col)-1))
Here is a breakdown: 1. find_in_set() will return the position of 'element_to_remove' in my_col, starting at 1 2. since bit arithmetic is starting at 0, you must remove 1 3. converting that number to a power of 2 with pow() 4. taking the floor in case 'element_to_remove' isn't present in my_col to start with, which gives pow(2,-1) = 0.5 so the floor of that is zero