kimmking edited a comment on issue #4947: Is there any way to traverse tables 
in the specified order by Schema & Table Route
URL: 
https://github.com/apache/incubator-shardingsphere/issues/4947#issuecomment-604309108
 
 
   @GolderGao
   
   1. How to know which one with data, and which one without data? If you know 
the data with its month is 3, you can direct query with `select * from  
t_msg_20_3 where ...`, ShardingSphere support this sql.
   2. The 12 sharding tables is the same to ShardingSphere engine, no one is 
specially prior of others. If in your business semantics, they have an order to 
process one by one, I suggestion in native sql way. And Actually broadcasting 
12 sharding tables will be parallelly query and merged, it's faster than one by 
one queries for several times.
   
   In our further plan, query optimization is a big blueprint. 
   As your case above, I recommend optimization by rewriting `union all` with 
the same database rather than `broadcast` or `one by one query`.

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