Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 4)
    ExpressionList (children 1)
     Asterisk
    TablesInSelectQuery (children 3)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier t1
     TablesInSelectQueryElement (children 2)
      TableExpression (children 1)
       TableIdentifier t2
      TableJoin
     TablesInSelectQueryElement (children 2)
      TableExpression (children 1)
       Subquery (alias t3) (children 1)
        SelectWithUnionQuery (children 1)
         ExpressionList (children 1)
          SelectQuery (children 3)
           ExpressionList (children 1)
            Identifier a (alias x)
           TablesInSelectQuery (children 1)
            TablesInSelectQueryElement (children 1)
             TableExpression (children 1)
              TableIdentifier t3
           Function equals (children 1)
            ExpressionList (children 2)
             Function plus (children 1)
              ExpressionList (children 2)
               Identifier a
               Literal UInt64_1
             Identifier b
      TableJoin
    Function and (children 1)
     ExpressionList (children 3)
      Function equals (children 1)
       ExpressionList (children 2)
        Identifier t1.a
        Function if (children 1)
         ExpressionList (children 3)
          Function greater (children 1)
           ExpressionList (children 2)
            Identifier t2.b
            Literal UInt64_0
          Identifier t2.a
          Literal UInt64_0
      Function equals (children 1)
       ExpressionList (children 2)
        Identifier t2.a
        Identifier t3.x
      Literal UInt64_1
    Set
