If you plan to use the SQL generated by the Access query builder in other applications as discussed on the previous page, you'll need to be careful of some of the differences between Access SQL and other RDBMS's.
A. Table/Column Specification in the Expression Builder
We used the Expression Builder to combine the players' first and last names, and later to calculate their home run per at-bat ratio. Unfortunately, the Expression Builder specifies table/column names in a format that is unique to Access. Here is a simplified version of the HR/AB query that doesn't bother including names from the PLAYERS table:
SELECT STATS.PLAYER_ID, STATS.YEAR, [STATS]![AB]/[STATS]![HR] AS ABPERHR FROM STATS;
The brackets and exclamation point used in this expression is non-standard SQL and would not work outside of Access. A safer syntax would be to use the same table.column notation used earlier in the SELECT clause:
SELECT STATS.PLAYER_ID, STATS.YEAR, STATS.AB/STATS.HR AS ABPERHR FROM STATS;
Or, to leave out the parent table name altogether:
SELECT PLAYER_ID, YEAR, AB/HR AS ABPERHR FROM STATS;
Note that this modified syntax will work in Access.
B. String Concatenation
In our queries that combined the players' first and last names, the following syntax was used:
SELECT [PLAYERS]![FIRST_NAME] & ' ' & [PLAYERS]![LAST_NAME]....
As mentioned above, columns should be specified using the table.column notation rather than with brackets and exclamation points. In addition to the different column specification, the concatenation itself would also be done differently in other RDBMS's. While Access uses the & character for concatenation, the concatenation operator in standard SQL is ||. However, there is considerable variation in the adherence to this standard. For a comparison of a number of the major RDBMS's, see http://troels.arvin.dk/db/rdbms/#functions-concat.
One of the points of comparison in the linked page is whether there is automatic casting of values. All this is getting at is what happens if the developer tries to concatenate a string with some other data type (say, a number). Some SQL implementations will automatically cast, or convert, the number to a string. Others are less flexible and require the developer to perform such a cast explicitly.