A filter is an expression, which might include wildcard characters, that is applied to the content of a publication message to determine whether it matches a subscription.
Body.Name LIKE 'Smit%'
This means that the contents of a field called Name in the body of a publication message are extracted and compared with the string given in the expression. If the string in the message starts with the characters "Smit", the expression evaluates to TRUE and the publication is sent to the subscriber.
If you want to select publications using filters only, without specifying a topic, you can register a subscription with the required filter and a topic of "#" (all topics). You then receive publications on only those topics for which you have access authority.
This subscription results in all publications from all connected brokers being sent to the broker that is local to the subscriber. Therefore, for performance reasons, if you have set up a network of brokers, you are advised to not use this technique.
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