mysql query updating transactions(transactionID) that only exist(transactionID) once in other table
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I need to generate a mysql query similar to this:

Update TRANSACTION SET points = 0  WHERE TransactionID NOT IN(SELECT TransactionID,  COUNT(*)  FROM trans_products  GROUP BY TransactionID WHERE COUNT(*) > 1)

The point is that I need to update transactions in 'transaction' table that exist once in table 'trans_products'

Any help 
 