✨ support UNION statements

[joocer]

UNION wil likely require changes to the parser as it may need to dynamically get the statement being worked on from a list, rather than hard-coded to 0

[joocer]

[
   {
      "Query":{
         "with":"None",
         "body":{
            "SetOperation":{
               "op":"Union",
               "all":false,
               "left":{
                  "Select":{
                     "distinct":false,
                     "top":"None",
                     "projection":[
                        {
                           "UnnamedExpr":{
                              "Function":{
                                 "name":[
                                    {
                                       "value":"TIME",
                                       "quote_style":"None"
                                    }
                                 ],
                                 "args":[
                                    
                                 ],
                                 "over":"None",
                                 "distinct":false
                              }
                           }
                        }
                     ],
                     "from":[
                        
                     ],
                     "lateral_views":[
                        
                     ],
                     "selection":"None",
                     "group_by":[
                        
                     ],
                     "cluster_by":[
                        
                     ],
                     "distribute_by":[
                        
                     ],
                     "sort_by":[
                        
                     ],
                     "having":"None"
                  }
               },
               "right":{
                  "Select":{
                     "distinct":false,
                     "top":"None",
                     "projection":[
                        {
                           "UnnamedExpr":{
                              "Function":{
                                 "name":[
                                    {
                                       "value":"TIME",
                                       "quote_style":"None"
                                    }
                                 ],
                                 "args":[
                                    
                                 ],
                                 "over":"None",
                                 "distinct":false
                              }
                           }
                        }
                     ],
                     "from":[
                        
                     ],
                     "lateral_views":[
                        
                     ],
                     "selection":"None",
                     "group_by":[
                        
                     ],
                     "cluster_by":[
                        
                     ],
                     "distribute_by":[
                        
                     ],
                     "sort_by":[
                        
                     ],
                     "having":"None"
                  }
               }
            }
         },
         "order_by":[
            
         ],
         "limit":"None",
         "offset":"None",
         "fetch":"None"
      }
   }
]

[joocer]

Likely to be part of #808

[joocer]

#1017

[joocer]

have three outstanding issues:

SELECT * , even on the same table, doesn't resolve because of wildcard handling and pushdowns

SELECT * FROM $planets AS P1 UNION SELECT * FROM $planets AS P2;

ORDER BY not being in SELECT results in duplicate entries because the projection to get rid of the ORDERED columns is after the DISTINCT

(SELECT name FROM $planets AS P1  ORDER BY mass DESC) UNION (SELECT name FROM $planets ORDER BY diameter ASC)

Missing column, not diagnosed yet.

SELECT AVG(mass) FROM $planets AS p1 UNION SELECT SUM(diameter) FROM $planets 

[joocer]

SELECT * the only issue outstanding.

The first (LEFT) table is getting all of the columns, the RIGHT is handling like it's a COUNT(*) query (i.e. no columns explicitly referenced)