For the upcoming jOOQ 3.3, we’re now integrating support for the MS Access database through the JDBC-ODBC bridge, which is included in the JDK up until Java SE 7. Note that it will be removed in Java 8! Alternative access to access databases (pun intended) can be obtained through a hack involving ucanaccess, which is basically combining the HSQLDB parser with Jackcess, a low-level I/O library for MS Access database files.
MS Access is still an immensely popular relational database, ranking in the top 10 at db-engines.com’s DBMS ranking. Yet it has quirks. Many of them. One is the fact that there is no formal CROSS JOIN operation. Remember, most databases support explicit CROSS JOINing as such:
SELECT p1.name player1, p2.name player2 FROM player p1 CROSS JOIN player p2
The above query will generate all the pairings between two players.
The same can be written in pre-ANSI SQL-92 with comma-separated table lists:
SELECT p1.name player1, p2.name player2 FROM player p1, player p2
The first syntax, however, is more powerful and more expressive as it can be used in nested JOIN expressions and it shows your intent more clearly. A nice example was given here in a previous blog post.
How to work around a missing CROSS JOIN
Usually, missing support for
CROSS JOIN can be emulated trivially using an
INNER JOIN with a
TRUE predicate as such:
SELECT p1.name player1, p2.name player2 FROM player p1 JOIN player p2 ON 1 = 1
This is what jOOQ does for the Sybase Adaptive Server Enterprise database. But this doesn’t work for MS Access, because the
JOIN operation there explicitly requires column references from either table on either side. The documentation reads:
Syntax:FROM table1 INNER JOIN table2 ON table1.field1 compopr table2.field2
This is quite a bummer from many points of view, not only for
CROSS JOIN emulation. Given that any ANSI-92
JOIN syntax can be transformed into an ANSI-86 join expression (table list in the
FROM clause and all predicates in the
WHERE clause), it is also a bit surprising.
A simple workaround that seems to work for some use-cases is to take any numeric column from either table, and multiply it by zero:
SELECT p1.name player1, p2.name player2 FROM player p1 JOIN player p2 ON p1.id * 0 = p2.id * 0
But if the database itself is already this quirky, I suspect that it might not be able to optimise the above SQL.
MS Access does not support
CROSS JOIN. For the time being, try to work around it using comma-separated table lists, while we work out more sophisticated SQL transformation in jOOQ.