use odbc_tables($con, "%") to get a list of all available catalogs (databases).
use odbc_tables($con, "", "%") to get a list of all schemas available.
use odbc_tables($con, "", "", "", "%") to get a list of all table types available.
use odbc_tables($con, "my catalog", "my schema", "%", "'TABLE', 'VIEW'") to get a list of all tables available.
using odbc_tables($con, "%", "%", "%", "%") will return an empty array !
Before PHP 4.0.3 uou could use this function with 1 or 5 prarms. From 4.0.3 the function matches the documentation.