Some options are “boolean” and 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
The values ON
, TRUE
,
OFF
, and FALSE
are also
recognized for boolean options (not case-sensitive).
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 '--loose-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.
The --maximum
prefix is available for
mysqld only and permits a limit to be placed on
how large client programs can set session system variables. To do
this, use a --maximum
prefix with the variable
name. For example,
--maximum-max_heap_table_size=32M
prevents any
client from making the heap table size limit larger than 32M.
The --maximum
prefix is intended for use with
system variables that have a session value. If applied to a system
variable that has only a global value, an error occurs. For
example, with --maximum-back_log=200
, the server
produces this error:
Maximum value of 'back_log' cannot be set