Creating a parse tree for a SQL statement

Question

Given the following statement and ignoring any grammar concerns, what might be the most 'pure' way to parse the following SQL statement?

SELECT a, b AS x FROM tbl AS z

My thinking is something along the following:

               selectStatement
                     |
                  SELECT
                  /     \
            selectList  FROM
              /   \          \
     selectItem   selectItem  tableExpression
          |          /  \         |
          a         b   AS       tableItem
                         |     /     \
                         x  tbl      AS
                                      \
                                       z

Is that a more or less accurate representation of this? If not, where could it be improved? Sometimes I have a difficult time determining whether a keyword should be a parse node or not (for example should AS be a separate node, or should there just be some sort of label on the alias node, and are 'labels' valid in a parse tree?).