strongduanmu opened a new issue #13900:
URL: https://github.com/apache/shardingsphere/issues/13900


   ## Feature Request
   
   Currently, union and union all statements only support single tables, which 
limits the user's usage scenarios, so we hope to support union and union all 
statements in sharding scenarios. For each subquery in the union and union all 
statements, if it can be routed to the same shard, it is supported by the 
simple push down engine, otherwise it is supported by the federation execution 
engine.
   
   Now, the union statement containing a sharding table will have the following 
exceptions.
   
   ```sql
   select order_id from t_order union select id from  t_single_table;
   ```
   
   ```
   ERROR 1997 (C1997): Runtime exception: [SELECT ... UNION statement can not 
support sharding tables or broadcast tables.]
   ```
   
   ### Is your feature request related to a problem?
   
   No.
   
   ### Describe the feature you would like.
   


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