isMultiBit

true for a multi-bit BIT(M) column, M > 1, in MySQL and MariaDB.

Both drivers return a byte[] for such a column, but neither reports a column class the default mapping recognizes as one: MySQL reports java.lang.Boolean, and MariaDB reports byte[] — the source-code spelling, not the "[B" JVM binary name the default mapping looks for. So both used to fall through to the java.sql.Types.BIT default, Boolean, which does not match the values (see #2087). A single-bit column really is a Boolean and is left alone.

The declared column width is the only thing in the metadata that tells the two apart, and it is TableColumnMetadata.size — which is 0 when the driver does not report a display size at all. A BIT(M) column of unknown width therefore still maps to Boolean; both drivers do report the width, so this is a fallback for a driver that does not rather than a case seen in practice.