Explain EXPLAIN (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 3)
    ExpressionList (children 1)
     Literal UInt64_1
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier test (alias t1)
    Function exists (children 1)
     ExpressionList (children 1)
      Subquery (children 1)
       SelectWithUnionQuery (children 1)
        ExpressionList (children 1)
         SelectQuery (children 3)
          ExpressionList (children 1)
           Asterisk
          TablesInSelectQuery (children 1)
           TablesInSelectQueryElement (children 1)
            TableExpression (children 1)
             TableIdentifier test (alias t2)
          Function equals (children 1)
           ExpressionList (children 2)
            Identifier t1.i1
            Identifier t2.i2
