MySQL Reference Manual - 4.0.20

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13.8.4 Miscellaneous Functions

FORMAT(X,D)

Formats the number X to a format like '#,###,###.##', rounded to D decimals, and returns the result as a string. If D is 0, the result will have no decimal point or fractional part.

mysql> SELECT FORMAT(12332.123456, 4);
        -> '12,332.1235'
mysql> SELECT FORMAT(12332.1,4);
        -> '12,332.1000'
mysql> SELECT FORMAT(12332.2,0);
        -> '12,332'

GET_LOCK(str,timeout)

Tries to obtain a lock with a name given by the string str, with a timeout of timeout seconds. Returns 1 if the lock was obtained successfully, 0 if the attempt timed out (for example, because another client has already locked the name), or NULL if an error occurred (such as running out of memory or the thread was killed with mysqladmin kill). If you have a lock obtained with GET_LOCK(), it is released when you execute RELEASE_LOCK(), execute a new GET_LOCK(), or your connection terminates (either normally or abnormally).

This function can be used to implement application locks or to simulate record locks. Names are locked on a server-wide basis. If a name has been locked by one client, GET_LOCK() blocks any request by another client for a lock with the same name. This allows clients that agree on a given lock name to use the name to perform cooperative advisory locking.

mysql> SELECT GET_LOCK('lock1',10);
        -> 1
mysql> SELECT IS_FREE_LOCK('lock2');
        -> 1
mysql> SELECT GET_LOCK('lock2',10);
        -> 1
mysql> SELECT RELEASE_LOCK('lock2');
        -> 1
mysql> SELECT RELEASE_LOCK('lock1');
        -> NULL

Note that the second RELEASE_LOCK() call returns NULL because the lock 'lock1' was automatically released by the second GET_LOCK() call.

INET_ATON(expr)

Given the dotted-quad representation of a network address as a string, returns an integer that represents the numeric value of the address. Addresses may be 4- or 8-byte addresses.

mysql> SELECT INET_ATON('209.207.224.40');
        -> 3520061480

The generated number is always in network byte order. For the example just shown, the number is calculated as 209*256^3 + 207*256^2 + 224*256 + 40.

As of MySQL 4.1.2, INET_ATON() also understands short-form IP addresses:

mysql> SELECT INET_ATON('127.0.0.1'), INET_ATON('127.1');
        -> 2130706433, 2130706433

INET_ATON() was added in MySQL 3.23.15.

INET_NTOA(expr)

Given a numeric network address (4 or 8 byte), returns the dotted-quad representation of the address as a string.

mysql> SELECT INET_NTOA(3520061480);
        -> '209.207.224.40'

INET_NTOA() was added in MySQL 3.23.15.

IS_FREE_LOCK(str)

Checks whether the lock named str is free to use (that is, not locked). Returns 1 if the lock is free (no one is using the lock), 0 if the lock is in use, and NULL on errors (such as incorrect arguments).

IS_FREE_LOCK() was added in MySQL 4.0.2.

IS_USED_LOCK(str)

Checks whether the lock named str is in use (that is, locked). If so, it returns the connection identifier of the client that holds the lock. Otherwise, it returns NULL.

IS_USED_LOCK() was added in MySQL 4.1.0.

MASTER_POS_WAIT(log_name,log_pos[,timeout])

This function is useful for control of master/slave synchronization. It blocks until the slave has read and applied all updates up to the specified position in the master log. The return value is the number of log events it had to wait for to get to the specified position. The function returns NULL if the slave SQL thread is not started, the slave's master information is not initialized, the arguments are incorrect, or an error occurs. It returns -1 if the timeout has been exceeded. If the slave SQL thread stops while MASTER_POS_WAIT() is waiting, the function returns NULL. If the slave is already past the specified position, the function returns immediately.

If a timeout value is specified, MASTER_POS_WAIT() stops waiting when timeout seconds have elapsed. timeout must be greater than 0; a zero or negative timeout means no timeout.

MASTER_POS_WAIT() was added in MySQL 3.23.32. The timeout argument was added in 4.0.10.

RELEASE_LOCK(str)

Releases the lock named by the string str that was obtained with GET_LOCK(). Returns 1 if the lock was released, 0 if the lock wasn't locked by this thread (in which case the lock is not released), and NULL if the named lock didn't exist. The lock will not exist if it was never obtained by a call to GET_LOCK() or if it already has been released.

The DO statement is convenient to use with RELEASE_LOCK(). See section DO.

UUID()

Returns a Universal Unique Identifier (UUID) generated according to "DCE 1.1: Remote Procedure Call" (Appendix A) CAE (Common Applications Environment) Specifications published by The Open Group in October 1997 (Document Number C706).

A UUID is designed as a number that is globally unique in space and time. Two calls to UUID() are expected to generate two different values, even if these calls are performed on two separate computers that are not connected to each other.

A UUID is a 128-bit number represented by a string of five hexadecimal numbers in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee format:

The first three numbers are generated from a timestamp.
The fourth number preserves temporal uniqueness in case the timestamp value loses monotonicity (for example, due to daylight saving time).
The fifth number is an IEEE 802 node number that provides spatial uniqueness. A random number is substituted if the latter is not available (for example, because the host computer has no Ethernet card, or we do not know how to find the hardware address of an interface on your operating system). In this case, spatial uniqueness cannot be guaranteed. Nevertheless, a collision should have very low probability.
Currently, the MAC address of an interface is taken into account only on FreeBSD and Linux. On other operating systems, MySQL uses a randomly generated 48-bit number.

mysql> SELECT UUID();
        -> '6ccd780c-baba-1026-9564-0040f4311e29'

Note that UUID() does not yet work with replication.

UUID() was added in MySQL 4.1.2.