mysql - Making a sql column UNIQUE -


this question has answer here:

is there anyway make column in mysql unique out removing , adding again ? know how add need remove first want edit current column , make unique

i 

alter table users add unique (username)

but tells me column username ready there . when want edit , not add it...

  1. could unique index there?
  2. could there duplicates in column?

check mysql - make field unique might fix problem.


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