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) ; → 2CURRENT_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.comDATABASE
database_name=DATABASE( )
DATABASE returns the name
of the database currently in use.
USE prod;
SET var1=database( ); → prodGET_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 ...