Check Unique Values

Check Unique Values

Could you help me with this problem.

I need to check a field call Ticket number with the all previous ticket numbers (on DB of incident request) is somebody has not created a incident ticket with number yet because it is not possible to duplicate that value.
is it possible using a rule that it execute a script

the format of our Ticket ID (IS-YYMMDD-XX)
Thanks in advance for you help

Kind regards
Carlos Armas

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