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The JDBC specification (like the ODBC specification) acknowledges the fact that some vendor specific SQL may be required for certain RDBMS features. To aid developers in writing portable JDBC applications across multiple database products, a special escape syntax is used to specify the generic commands the developer wants to be run. The JDBC driver translates these escape sequences into native syntax for its specific database. For more information consult the section 4.1.5 from the JDBC Technology Guide (bundled with the Sun™ JRE documentation) and the section 13.4 from the JDBC 3.0 specification.
The parsing of the sql statements for these escapes can be disabled using Statement.setEscapeProcessing(false).
Connection.nativeSQL(String sql) provides another way to have escapes processed.
It translates the given SQL to a SQL suitable for the PostgreSQL™ backend.
Example 8.1. Using jdbc escapes
To use the JDBC escapes, you simply write your SQL replacing date/time literal values, outer join and functions by the JDBC escape syntax. For example :
ResultSet rs = st.executeQuery("SELECT {fn week({d '2005-01-24'})}");
is the portable version for
ResultSet rs = st.executeQuery("SELECT extract(week from DATE '2005-01-24')");
You can specify which escape character to use in strings comparison (with LIKE) to protect wildcards
characters ('%' and '_') by adding the following escape : {escape 'escape-character'}.
The driver supports this only at the end of the comparison expression.
For example, you can compare string values using '|' as escape character to protect '_' :
rs = stmt.executeQuery("select str2 from comparisontest where str1 like '|_abcd' {escape '|'} ");