Explain EXPLAIN QUERY TREE (children 2)
 Set
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 2)
    ExpressionList (children 1)
     Function count (children 1)
      ExpressionList
    TablesInSelectQuery (children 2)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       TableIdentifier x
     TablesInSelectQueryElement (children 2)
      TableExpression (children 1)
       TableIdentifier y
      TableJoin (children 1)
       Function or (children 1)
        ExpressionList (children 2)
         Function and (children 1)
          ExpressionList (children 2)
           Function equals (children 1)
            ExpressionList (children 2)
             Identifier x.A
             Identifier y.A
           Function equals (children 1)
            ExpressionList (children 2)
             Identifier x.B
             Literal UInt64_1
         Function and (children 1)
          ExpressionList (children 2)
           Function equals (children 1)
            ExpressionList (children 2)
             Identifier x.A
             Identifier y.A
           Function equals (children 1)
            ExpressionList (children 2)
             Identifier y.C
             Literal UInt64_1
