Fix escaping wildcards in column lookup and make escaping optional

[ckunki]

Based on issue #136 VSCJDBC release 10.4.0 introduced escaped wildcards when looking up column metadata which was implemented in BaseColumnMetadataReader.getColumnMetadata().

This seems to work fine for exasol-virtual-schema as demonstrated by a related test.

Unfortunately the Oracle JDBC driver seems to deviate from JDBC standard in the way that escaped wildcards in the name of a database schema or a table lead to no matching columns found. So the change introduced with #136 needs to be rolled back for ORAVS and maybe other virtual schemas as well.

See

• https://github.com/exasol/oracle-virtual-schema/issues/30.
• Oracle API documentation on OracleDatabaseMetaData.html.getColumns() and getSearchStringEscape()

The current ticket therefore proposes to make the wildcard escaping optional by providing a method that SQL dialects inheriting from VSCJDBC can override in order to escape wildcards.

Later on

• VSEXA can then be updated overriding the method and escaping wildcards, see https://github.com/exasol/exasol-virtual-schema/issues/99
• VSORA can then simply update the dependency to VSCJDBC without breaking the functionality
• other VS can make a decision on their own
• default will be no escaping in order to avoid unexpected problems.

[ckunki]

Proposal: VSCJDBC, class BaseColumnMetadataReader:

  protected ResultSet getColumnMetadata(final String catalogName, final String schemaNamePattern,
            final String tableNamePattern) throws SQLException {
        return this.connection.getMetaData().getColumns(catalogName, 
              schemaNamePattern, tableNamePattern, ANY_COLUMN);
    }

Proposal: VSEXA class ExasolColumnMetadataReader extends BaseColumnMetadataReader:

    @Override
    protected ResultSet getColumnMetadata(final String catalogName, final String schemaNamePattern,
            final String tableNamePattern) throws SQLException {
        return this.connection.getMetaData().getColumns(catalogName, 
                Wildcards.escape(schemaNamePattern),
                Wildcards.escape(tableNamePattern), ANY_COLUMN);
    }

[ckunki]

Additional fixes	Problem	Fix
VSCJDBC also escaped wild cards in the name of the database catalog, conflicting with the parameter's documentation as literal string.	Do not escape potential wild cards in the name of the database catalog.
VSCJDBC always used the backslash as escape string, while there are SQL dialects with different escape string, e.g. VSORA using a forward slash /.	Use java.sql.DatabaseMetaData.getSearchStringEscape() to inquire the escape string for the specific SQL dialect.