How to create stored procedure using H2 database?

Question

Has anyone tried to create stored procedures using the H2 database?

Answer 1

To access the database within a Java function, you do need a connection. For H2, there are two ways to get such a connection:

Solution 1: If the first parameter of the Java function is a java.sql.Connection, then the database provides the connection. For SQL, this is a 'hidden' parameter, meaning you can't and don't need to set it explicitly. This is documented: User-Defined Functions and Stored Procedures, "Functions That Require a Connection". Example:

CREATE ALIAS QUERY AS $$
ResultSet query(Connection conn, String sql) throws SQLException {
    return conn.createStatement().executeQuery(sql);
} $$;
CALL QUERY('SELECT * FROM DUAL');

Solution 2: For compatibility with Apache Derby and Oracle, You can open a new connection within the Java function using DriverManager.getConnection("jdbc:default:connection"). This feature is available in H2 version 1.3.151 and newer, and it it disabled by default. To enable it, append ;DEFAULT_CONNECTION=TRUE to the database URL. It's a problematic feature because the Oracle JDBC driver will try to resolve this database URL if it is loaded before the H2 driver. So basically you can't use the feature if the Oracle driver is loaded (I consider this a bug in the Oracle driver).