Java Enterprise in a Nutshell, Third Edition

Escape Sequences

Escape sequences allow JDBC programs to package certain database commands in a database-independent manner. Since different databases implement different features (especially scalar SQL functions) in different ways, in order to be truly portable, JDBC needs to provide a standard way to access at least a subset of that functionality. We’ve already seen escape sequences twice: with the various SQL date and time functions and with the CallableStatement object.

A JDBC escape sequence consists of a pair of curly braces, a keyword, and a set of parameters. Thus, call is the keyword for stored procedures, while d, t, and ts are keywords for dates and times. One keyword we haven’t seen yet is escape. This keyword specifies the character that is used to escape wildcard characters in a LIKE statement:

stmt.executeQuery(
 "SELECT * FROM ApiDocs WHERE Field_Name like 'TRANS\_%' {escape '\'}");

Normally, the underscore character (_ ) is treated as a single-character wildcard, while the percent sign (%) is the multiple-character wildcard. By specifying the backslash (\) as the escape character, we can match on the underscore character itself. Note that the escape keyword can also be used outside wildcard searches. For example, SQL string termination characters (such as the single quote) need to be escaped when appearing within strings.

The fn keyword allows the use of internal scalar database functions . Scalar functions are a fairly standard component of most database architectures, ...