QueryDatabaseTable does not support incoming connections, so you wouldn't be able to support multiple tables. The "Table Name" property does support NiFi Expression Language, but that is so you can migrate flows from dev to test to production using different table names, each environment would have its own (static) variable set. Instead, you can use GenerateTableFetch, it supports incoming connections and thus you can use flow file attributes in the expression(s) for Table Name, Columns to Return, Maximum-value Columns, etc. It works like QueryDatabaseTable, but instead of generating and executing the SQL, it only generates the SQL statements. This allows you to send the statements downstream to something like ExecuteSQL, possibly distributing the flow files among nodes in the cluster (using a Remote Process Group -> Input Port, if you have a cluster vs a standalone NiFi instance). You can populate your incoming flow files from wherever you get your configuration (ListFile -> FetchFile if it is a file on disk, ListDatabaseTables if you want to get a list of tables from the database itself).
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