This is part 4 in a 3-part series (take that, Douglas Adams ;-). You can see parts 1 and 2 here and part 3 here.

A little background: the reason I am so concerned portability is the Solar project. One of the stated goals for Solar_Sql (the RDBMS abstraction layer) is that it should run exactly the same way on every supported database. Right now, that list includes Frontbase, Microsoft SQL, MySQL, PostgreSQL, and SQLite.

Case-Sensitivity in WHERE Clauses

Let's say we have a table with a column named "the_field" defined as CHAR(2). In the table, we have every possible combination of two letters, picked from the set of all upper-case and lower case letters (i.e., "A-Z" and "a-z", for a total of 26^2 rows in the table). For example, the "A" combinations are represented by four rows: "aa", "aA", "Aa", and "AA".

In theory, if you wanted to select the row with "aa" (where both are lower case), you would issue this SELECT statement:

SELECT * FROM the_table WHERE the_field = 'aa'

How many rows will you get back? You should only get one: the "aa" row. That's true if the database is PostgreSQL, Frontbase, or SQLite; however, in Microsoft SQL and MySQL, you get four ("aa", "aA", "Aa", and "AA"). That's because searches in those two RDBMSes are *not* case-sensitive on CHAR and VARCHAR fields. This fails to meet my requirement that Solar_Sql return the same results regardless of the backend.

I think the solution will be to re-define the native type used for "char" and "varchar" fields in those two databases. It turns out that in MySQL, a "CHAR(n) BINARY" and "VARCHAR(n) BINARY" both retain case-sensitivity in searches. In Microsoft SQL, the same appears to be true for "BINARY" (vice "CHAR") and "VARBINARY" (vice "VARCHAR").

Does anyone see a problem with using the binary types instead of the plain character types in those two databases, specifically for purposes of case-sensitivity? My appreciation will extend to buying you a beer next time we're in the same town. :-)

Are you stuck with a legacy PHP application? You should buy my book because it gives you a step-by-step guide to improving you codebase, all while keeping it running the whole time.