Explain EXPLAIN (children 2)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 1)
     Function count (children 1)
      ExpressionList
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier t_skip_index_in
    Function in (children 1)
     ExpressionList (children 2)
      Identifier c
      Subquery (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 1)
         SelectQuery (children 1)
          ExpressionList (children 1)
           Function throwIf (children 1)
            ExpressionList (children 1)
             Literal UInt64_1
    Set
 Identifier Null
