MySQL 4.0.2 introduced some additional flexibility in the way you specify options. SQL 4.0.2. Some of these changes relate to the way you specify options that have “enabled” and “disabled” states, and to the use of options that might be present in one version of MySQL but not another. Those capabilities are discussed in this section.

Some options are “boolean” and control behavior that can be turned on or off. Some options control behavior that can be turned on or off. For example, the mysql client supports a --column-names option that determines whether or not to display a row of column names at the beginning of query results. By default, this option is enabled. However, you may want to disable it in some instances, such as when sending the output of mysql into another program that expects to see only data and not an initial header line.

To disable column names, you can specify the option using any of these forms:

--disable-column-names
--skip-column-names
--column-names=0

The --disable and --skip prefixes and the =0 suffix all have the same effect: They turn the option off.

The “enabled” form of the option may be specified in any of these ways:

--column-names
--enable-column-names
--column-names=1

Another change to option processing introduced in MySQL 4.0.2 is that you can use the --loose prefix for command-line options. If an option is prefixed by --loose, a program does not exit with an error if it does not recognize the option, but instead issues only a warning:

shell> mysql --loose-no-such-option
mysql: WARNING: unknown option '--no-such-option'

The --loose prefix can be useful when you run programs from multiple installations of MySQL on the same machine and list options in an option file, An option that may not be recognized by all versions of a program can be given using the --loose prefix (or loose in an option file). Versions of the program that recognize the option process it normally, and versions that do not recognize it issue a warning and ignore it. This strategy requires that all versions involved be 4.0.2 or later, because earlier versions know nothing of the --loose convention.

As of MySQL 4.0.2, mysqld enables a limit to be placed on how large client programs can set dynamic system variables. To do this, use a --maximum prefix with the variable name. For example, --maximum-query_cache_size=4M prevents any client from making the query cache size larger than 4MB.