DEFAULT(col_name)

Returns the default value for a table column.

mysql> UPDATE t SET i = DEFAULT(i)+1 WHERE id < 100;

DEFAULT() was added in MySQL 4.1.0.

FORMAT(X,D)

Formats the number X to a format like '#,###,###.##', rounded to D decimal places, and returns the result as a string. For details, see Section 11.5, “String Functions”.

GET_LOCK(str,timeout)

Tries to obtain a lock with a name given by the string str, using 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 previously 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). Locks obtained with GET_LOCK() do not interact with transactions. That is, committing a transaction does not release any such locks obtained during the transaction.

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 enables clients that agree on a given lock name to use the name to perform cooperative advisory locking. But be aware that it also enables a client that is not among the set of cooperating clients to lock a name, either inadvertently or deliberately, and thus prevent any of the cooperating clients from locking that name. One way to reduce the likelihood of this is to use lock names that are database-specific or application-specific. For example, use lock names of the form db_name.str or app_name.str.

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

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

If multiple clients are waiting for a lock, the order in which they will acquire it is undefined and depends on factors such as the thread library in use. In particular, applications should not assume that clients will acquire the lock in the same order that they issued the lock requests.

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 209×256³ + 207×256² + 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 in network byte order (4 or 8 byte), returns the dotted-quad representation of the address as a binary 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 if an error occurs (such as an incorrect argument).

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 the slave had to wait for to advance 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 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 was not established by this thread (in which case the lock is not released), and NULL if the named lock did not exist. The lock does not exist if it was never obtained by a call to GET_LOCK() or if it has previously been released.

The DO statement is convenient to use with RELEASE_LOCK(). See Section 12.2.2, “DO Syntax”.

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, http://www.opengroup.org/public/pubs/catalog/c706.htm).

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 utf8 string of five hexadecimal numbers in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee format:

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

UUID() was added in MySQL 4.1.2.

VALUES(col_name)

In an INSERT ... ON DUPLICATE KEY UPDATE statement, you can use the VALUES(col_name) function in the UPDATE clause to refer to column values from the INSERT portion of the statement. In other words, VALUES(col_name) in the UPDATE clause refers to the value of col_name that would be inserted, had no duplicate-key conflict occurred. This function is especially useful in multiple-row inserts. The VALUES() function is meaningful only in the ON DUPLICATE KEY UPDATE clause of INSERT statements and returns NULL otherwise. See Section 12.2.4.3, “INSERT ... ON DUPLICATE KEY UPDATE Syntax”.

mysql> INSERT INTO table (a,b,c) VALUES (1,2,3),(4,5,6)
    -> ON DUPLICATE KEY UPDATE c=VALUES(a)+VALUES(b);

VALUES() was added in MySQL 4.1.1.