Other Functions
The miscellaneous built-in functions described in the following sections perform operations that do not fall into the categories described in earlier sections.
BENCHMARK
zero
=BENCHMARK
(no_of_repeats
,expression
)
BENCHMARK
executes the
specified expression repeatedly. It is intended to be used to
benchmark MySQL performance. This function has very little
applicability in a stored program context, although in theory you
could use it to repeatedly execute a stored program.
COALESCE
value
=COALESCE
(value
[,...])
COALESCE
returns the first
non-NULL value in the provided list of values.
SET var1=1; → 1 SET var2=2; → 2 SET var3=NULL; → SET var4=COALESCE(var1,var2,var3); → 1 SET var5=COALESCE(var3,var2,var1) ; → 2
CURRENT_USER
username
=CURRENT_USER
( )
CURRENT_USER
returns the
username and hostname of the current MySQL user. It may report a
different value from that returned by USER
, since the USER
function reports the connection
requested by the user, rather than the connection that was actually
used.
SET var1=CURRENT_USER( ); → root@% SET var2=USER( ); → root@mel601439.quest.com
DATABASE
database_name
=DATABASE
( )
DATABASE
returns the name
of the database currently in use.
USE prod; SET var1=database( ); → prod
GET_LOCK
return_code
=GET_LOCK(lock_name
,timeout
)
GET_LOCK
allows you to
define and acquire a user-defined lock. The
lock_name
can be a string of your choice.
GET_LOCK
will attempt to acquire the lock; then, if no other session holds the lock, it will return ...
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