12.23 Miscellaneous Functions

Table 12.29 Miscellaneous Functions

Name	Description
ANY_VALUE()	Suppress ONLY_FULL_GROUP_BY value rejection
BIN_TO_UUID()	Convert binary UUID to string
DEFAULT()	Return the default value for a table column
GROUPING()	Distinguish super-aggregate ROLLUP rows from regular rows
INET_ATON()	Return the numeric value of an IP address
INET_NTOA()	Return the IP address from a numeric value
INET6_ATON()	Return the numeric value of an IPv6 address
INET6_NTOA()	Return the IPv6 address from a numeric value
IS_IPV4()	Whether argument is an IPv4 address
IS_IPV4_COMPAT()	Whether argument is an IPv4-compatible address
IS_IPV4_MAPPED()	Whether argument is an IPv4-mapped address
IS_IPV6()	Whether argument is an IPv6 address
IS_UUID()	Whether argument is a valid UUID
MASTER_POS_WAIT()	Block until the slave has read and applied all updates up to the specified position
NAME_CONST()	Cause the column to have the given name
RAND()	Return a random floating-point value
SLEEP()	Sleep for a number of seconds
UUID()	Return a Universal Unique Identifier (UUID)
UUID_SHORT()	Return an integer-valued universal identifier
UUID_TO_BIN()	Convert string UUID to binary
VALUES()	Define the values to be used during an INSERT

• ANY_VALUE(arg)

  This function is useful for GROUP BY queries when the ONLY_FULL_GROUP_BY SQL mode is enabled, for cases when MySQL rejects a query that you know is valid for reasons that MySQL cannot determine. The function return value and type are the same as the return value and type of its argument, but the function result is not checked for the ONLY_FULL_GROUP_BY SQL mode.

  For example, if name is a nonindexed column, the following query fails with ONLY_FULL_GROUP_BY enabled:

  mysql> SELECT name, address, MAX(age) FROM t GROUP BY name;
  ERROR 1055 (42000): Expression #2 of SELECT list is not in GROUP
  BY clause and contains nonaggregated column 'mydb.t.address' which
  is not functionally dependent on columns in GROUP BY clause; this
  is incompatible with sql_mode=only_full_group_by

  The failure occurs because address is a nonaggregated column that is neither named among GROUP BY columns nor functionally dependent on them. As a result, the address value for rows within each name group is nondeterministic. There are multiple ways to cause MySQL to accept the query:

  • Alter the table to make name a primary key or a unique NOT NULL column. This enables MySQL to determine that address is functionally dependent on name; that is, address is uniquely determined by name. (This technique is inapplicable if NULL must be permitted as a valid name value.)

  • Use ANY_VALUE() to refer to address:

    SELECT name, ANY_VALUE(address), MAX(age) FROM t GROUP BY name;

    In this case, MySQL ignores the nondeterminism of address values within each name group and accepts the query. This may be useful if you simply do not care which value of a nonaggregated column is chosen for each group. ANY_VALUE() is not an aggregate function, unlike functions such as SUM() or COUNT(). It simply acts to suppress the test for nondeterminism.

  • Disable ONLY_FULL_GROUP_BY. This is equivalent to using ANY_VALUE() with ONLY_FULL_GROUP_BY enabled, as described in the previous item.

  ANY_VALUE() is also useful if functional dependence exists between columns but MySQL cannot determine it. The following query is valid because age is functionally dependent on the grouping column age-1, but MySQL cannot tell that and rejects the query with ONLY_FULL_GROUP_BY enabled:

  SELECT age FROM t GROUP BY age-1;

  To cause MySQL to accept the query, use ANY_VALUE():

  SELECT ANY_VALUE(age) FROM t GROUP BY age-1;

  ANY_VALUE() can be used for queries that refer to aggregate functions in the absence of a GROUP BY clause:

  mysql> SELECT name, MAX(age) FROM t;
  ERROR 1140 (42000): In aggregated query without GROUP BY, expression
  #1 of SELECT list contains nonaggregated column 'mydb.t.name'; this
  is incompatible with sql_mode=only_full_group_by

  Without GROUP BY, there is a single group and it is nondeterministic which name value to choose for the group. ANY_VALUE() tells MySQL to accept the query:

  SELECT ANY_VALUE(name), MAX(age) FROM t;

  It may be that, due to some property of a given data set, you know that a selected nonaggregated column is effectively functionally dependent on a GROUP BY column. For example, an application may enforce uniqueness of one column with respect to another. In this case, using ANY_VALUE() for the effectively functionally dependent column may make sense.

  For additional discussion, see Section 12.20.3, “MySQL Handling of GROUP BY”.

• BIN_TO_UUID(binary_uuid), BIN_TO_UUID(binary_uuid, swap_flag)

  BIN_TO_UUID() is the inverse of UUID_TO_BIN(). It converts a binary UUID to a string UUID and returns the result. The binary value should be a UUID as a VARBINARY(16) value. The return value is a utf8 string of five hexadecimal numbers separated by dashes. (For details about this format, see the UUID() function description.) If the UUID argument is NULL, the return value is NULL. If any argument is invalid, an error occurs.

  BIN_TO_UUID() takes one or two arguments:

  • The one-argument form takes a binary UUID value. The UUID value is assumed not to have its time-low and time-high parts swapped. The string result is in the same order as the binary argument.

  • The two-argument form takes a binary UUID value and a swap-flag value:

    • If swap_flag is 0, the two-argument form is equivalent to the one-argument form. The string result is in the same order as the binary argument.

    • If swap_flag is 1, the UUID value is assumed to have its time-low and time-high parts swapped. These parts are swapped back to their original position in the result value.

  For usage examples and information about time-part swapping, see the UUID_TO_BIN() function description.

• DEFAULT(col_name)

  Returns the default value for a table column. An error results if the column has no default value.

  The use of DEFAULT(col_name) to specify the default value for a named column is permitted only for columns that have a literal default value, not for columns that have an expression default value.

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

• 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 12.5, “String Functions”.

• GROUPING(expr [, expr] ...)

  For GROUP BY queries that include a WITH ROLLUP modifier, the ROLLUP operation produces super-aggregate output rows where NULL represents the set of all values. The GROUPING() function enables you to distinguish NULL values for super-aggregate rows from NULL values in regular grouped rows.

  GROUPING() is permitted only in the select list or HAVING clause.

  Each argument to GROUPING() must be an expression that exactly matches an expression in the GROUP BY clause. The expression cannot be a positional specifier. For each expression, GROUPING() produces 1 if the expression value in the current row is a NULL representing a super-aggregate value. Otherwise, GROUPING() produces 0, indicating that the expression value is a NULL for a regular result row or is not NULL.

  Suppose that table t1 contains these rows, where NULL indicates something like “other” or “unknown”:

  mysql> SELECT * FROM t1;
  +------+-------+----------+
  | name | size  | quantity |
  +------+-------+----------+
  | ball | small |       10 |
  | ball | large |       20 |
  | ball | NULL  |        5 |
  | hoop | small |       15 |
  | hoop | large |        5 |
  | hoop | NULL  |        3 |
  +------+-------+----------+

  A summary of the table without WITH ROLLUP looks like this:

  mysql> SELECT name, size, SUM(quantity) AS quantity
         FROM t1
         GROUP BY name, size;
  +------+-------+----------+
  | name | size  | quantity |
  +------+-------+----------+
  | ball | small |       10 |
  | ball | large |       20 |
  | ball | NULL  |        5 |
  | hoop | small |       15 |
  | hoop | large |        5 |
  | hoop | NULL  |        3 |
  +------+-------+----------+

  The result contains NULL values, but those do not represent super-aggregate rows because the query does not include WITH ROLLUP.

  Adding WITH ROLLUP produces super-aggregate summary rows containing additional NULL values. However, without comparing this result to the previous one, it is not easy to see which NULL values occur in super-aggregate rows and which occur in regular grouped rows:

  mysql> SELECT name, size, SUM(quantity) AS quantity
         FROM t1
         GROUP BY name, size WITH ROLLUP;
  +------+-------+----------+
  | name | size  | quantity |
  +------+-------+----------+
  | ball | NULL  |        5 |
  | ball | large |       20 |
  | ball | small |       10 |
  | ball | NULL  |       35 |
  | hoop | NULL  |        3 |
  | hoop | large |        5 |
  | hoop | small |       15 |
  | hoop | NULL  |       23 |
  | NULL | NULL  |       58 |
  +------+-------+----------+

  To distinguish NULL values in in super-aggregate rows from those in regular grouped rows, use GROUPING(), which returns 1 only for super-aggregate NULL values:

  mysql> SELECT
           name, size, SUM(quantity) AS quantity,
           GROUPING(name) AS grp_name,
           GROUPING(size) AS grp_size
         FROM t1
         GROUP BY name, size WITH ROLLUP;
  +------+-------+----------+----------+----------+
  | name | size  | quantity | grp_name | grp_size |
  +------+-------+----------+----------+----------+
  | ball | NULL  |        5 |        0 |        0 |
  | ball | large |       20 |        0 |        0 |
  | ball | small |       10 |        0 |        0 |
  | ball | NULL  |       35 |        0 |        1 |
  | hoop | NULL  |        3 |        0 |        0 |
  | hoop | large |        5 |        0 |        0 |
  | hoop | small |       15 |        0 |        0 |
  | hoop | NULL  |       23 |        0 |        1 |
  | NULL | NULL  |       58 |        1 |        1 |
  +------+-------+----------+----------+----------+

  Common uses for GROUPING():

  • Substitute a label for super-aggregate NULL values:

    mysql> SELECT
             IF(GROUPING(name) = 1, 'All items', name) AS name,
             IF(GROUPING(size) = 1, 'All sizes', size) AS size,
             SUM(quantity) AS quantity
           FROM t1
           GROUP BY name, size WITH ROLLUP;
    +-----------+-----------+----------+
    | name      | size      | quantity |
    +-----------+-----------+----------+
    | ball      | NULL      |        5 |
    | ball      | large     |       20 |
    | ball      | small     |       10 |
    | ball      | All sizes |       35 |
    | hoop      | NULL      |        3 |
    | hoop      | large     |        5 |
    | hoop      | small     |       15 |
    | hoop      | All sizes |       23 |
    | All items | All sizes |       58 |
    +-----------+-----------+----------+

  • Return only super-aggregate lines by filtering out the regular grouped lines:

    mysql> SELECT name, size, SUM(quantity) AS quantity
           FROM t1
           GROUP BY name, size WITH ROLLUP
           HAVING GROUPING(name) = 1 OR GROUPING(size) = 1;
    +------+------+----------+
    | name | size | quantity |
    +------+------+----------+
    | ball | NULL |       35 |
    | hoop | NULL |       23 |
    | NULL | NULL |       58 |
    +------+------+----------+

  GROUPING() permits multiple expression arguments. In this case, the GROUPING() return value represents a bitmask combined from the results for each expression, where the lowest-order bit corresponds to the result for the rightmost expression. For example, with three expression arguments, GROUPING(expr1, expr2, expr3) is evaluated like this:

    result for GROUPING(expr3)
  + result for GROUPING(expr2) << 1
  + result for GROUPING(expr1) << 2

  The following query shows how GROUPING() results for single arguments combine for a multiple-argument call to produce a bitmask value:

  mysql> SELECT
           name, size, SUM(quantity) AS quantity,
           GROUPING(name) AS grp_name,
           GROUPING(size) AS grp_size,
         GROUPING(name, size) AS grp_all
         FROM t1
         GROUP BY name, size WITH ROLLUP;
  +------+-------+----------+----------+----------+---------+
  | name | size  | quantity | grp_name | grp_size | grp_all |
  +------+-------+----------+----------+----------+---------+
  | ball | NULL  |        5 |        0 |        0 |       0 |
  | ball | large |       20 |        0 |        0 |       0 |
  | ball | small |       10 |        0 |        0 |       0 |
  | ball | NULL  |       35 |        0 |        1 |       1 |
  | hoop | NULL  |        3 |        0 |        0 |       0 |
  | hoop | large |        5 |        0 |        0 |       0 |
  | hoop | small |       15 |        0 |        0 |       0 |
  | hoop | NULL  |       23 |        0 |        1 |       1 |
  | NULL | NULL  |       58 |        1 |        1 |       3 |
  +------+-------+----------+----------+----------+---------+

  With multiple expression arguments, the GROUPING() return value is nonzero if any expression represents a super-aggregate value. Multiple-argument GROUPING() syntax thus provides a simpler way to write the earlier query that returned only super-aggregate rows, by using a single multiple-argument GROUPING() call rather than multiple single-argument calls:

  mysql> SELECT name, size, SUM(quantity) AS quantity
         FROM t1
         GROUP BY name, size WITH ROLLUP
         HAVING GROUPING(name, size) <> 0;
  +------+------+----------+
  | name | size | quantity |
  +------+------+----------+
  | ball | NULL |       35 |
  | hoop | NULL |       23 |
  | NULL | NULL |       58 |
  +------+------+----------+

  Use of GROUPING() is subject to these limitations:

  • Do not use subquery GROUP BY expressions as GROUPING() arguments because matching might fail. For example, matching fails for this query:

    mysql> SELECT GROUPING((SELECT MAX(name) FROM t1))
           FROM t1
           GROUP BY (SELECT MAX(name) FROM t1) WITH ROLLUP;
    ERROR 3580 (HY000): Argument #1 of GROUPING function is not in GROUP BY

  • GROUP BY literal expressions should not be used within a HAVING clause as GROUPING() arguments. Due to differences between when the optimizer evaluates GROUP BY and HAVING, matching may succeed but GROUPING() evaluation does not produce the expected result. Consider this query:

    SELECT a AS f1, 'w' AS f2
    FROM t
    GROUP BY f1, f2 WITH ROLLUP
    HAVING GROUPING(f2) = 1;

    GROUPING() is evaluated earlier for the literal constant expression than for the HAVING clause as a whole and returns 0. To check whether a query such as this is affected, use EXPLAIN and look for Impossible having in the Extra column.

  For more information about WITH ROLLUP and GROUPING(), see Section 12.20.2, “GROUP BY Modifiers”.

• INET_ATON(expr)

  Given the dotted-quad representation of an IPv4 network address as a string, returns an integer that represents the numeric value of the address in network byte order (big endian). INET_ATON() returns NULL if it does not understand its argument.

  mysql> SELECT INET_ATON('10.0.5.9');
          -> 167773449

  For this example, the return value is calculated as 10×256³ + 0×256² + 5×256 + 9.

  INET_ATON() may or may not return a non-NULL result for short-form IP addresses (such as '127.1' as a representation of '127.0.0.1'). Because of this, INET_ATON()a should not be used for such addresses.

  Note

  To store values generated by INET_ATON(), use an INT UNSIGNED column rather than INT, which is signed. If you use a signed column, values corresponding to IP addresses for which the first octet is greater than 127 cannot be stored correctly. See Section 11.2.6, “Out-of-Range and Overflow Handling”.

• INET_NTOA(expr)

  Given a numeric IPv4 network address in network byte order, returns the dotted-quad string representation of the address as a string in the connection character set. INET_NTOA() returns NULL if it does not understand its argument.

  mysql> SELECT INET_NTOA(167773449);
          -> '10.0.5.9'

• INET6_ATON(expr)

  Given an IPv6 or IPv4 network address as a string, returns a binary string that represents the numeric value of the address in network byte order (big endian). Because numeric-format IPv6 addresses require more bytes than the largest integer type, the representation returned by this function has the VARBINARY data type: VARBINARY(16) for IPv6 addresses and VARBINARY(4) for IPv4 addresses. If the argument is not a valid address, INET6_ATON() returns NULL.

  The following examples use HEX() to display the INET6_ATON() result in printable form:

  mysql> SELECT HEX(INET6_ATON('fdfe::5a55:caff:fefa:9089'));
          -> 'FDFE0000000000005A55CAFFFEFA9089'
  mysql> SELECT HEX(INET6_ATON('10.0.5.9'));
          -> '0A000509'

  INET6_ATON() observes several constraints on valid arguments. These are given in the following list along with examples.

  • A trailing zone ID is not permitted, as in fe80::3%1 or fe80::3%eth0.

  • A trailing network mask is not permitted, as in 2001:45f:3:ba::/64 or 198.51.100.0/24.

  • For values representing IPv4 addresses, only classless addresses are supported. Classful addresses such as 198.51.1 are rejected. A trailing port number is not permitted, as in 198.51.100.2:8080. Hexadecimal numbers in address components are not permitted, as in 198.0xa0.1.2. Octal numbers are not supported: 198.51.010.1 is treated as 198.51.10.1, not 198.51.8.1. These IPv4 constraints also apply to IPv6 addresses that have IPv4 address parts, such as IPv4-compatible or IPv4-mapped addresses.

  To convert an IPv4 address expr represented in numeric form as an INT value to an IPv6 address represented in numeric form as a VARBINARY value, use this expression:

  INET6_ATON(INET_NTOA(expr))

  For example:

  mysql> SELECT HEX(INET6_ATON(INET_NTOA(167773449)));
          -> '0A000509'

• INET6_NTOA(expr)

  Given an IPv6 or IPv4 network address represented in numeric form as a binary string, returns the string representation of the address as a string in the connection character set. If the argument is not a valid address, INET6_NTOA() returns NULL.

  INET6_NTOA() has these properties:

  • It does not use operating system functions to perform conversions, thus the output string is platform independent.

  • The return string has a maximum length of 39 (4 x 8 + 7). Given this statement:

    CREATE TABLE t AS SELECT INET6_NTOA(expr) AS c1;

    The resulting table would have this definition:

    CREATE TABLE t (c1 VARCHAR(39) CHARACTER SET utf8 DEFAULT NULL);

  • The return string uses lowercase letters for IPv6 addresses.

  mysql> SELECT INET6_NTOA(INET6_ATON('fdfe::5a55:caff:fefa:9089'));
          -> 'fdfe::5a55:caff:fefa:9089'
  mysql> SELECT INET6_NTOA(INET6_ATON('10.0.5.9'));
          -> '10.0.5.9'
  
  mysql> SELECT INET6_NTOA(UNHEX('FDFE0000000000005A55CAFFFEFA9089'));
          -> 'fdfe::5a55:caff:fefa:9089'
  mysql> SELECT INET6_NTOA(UNHEX('0A000509'));
          -> '10.0.5.9'

• IS_IPV4(expr)

  Returns 1 if the argument is a valid IPv4 address specified as a string, 0 otherwise.

  mysql> SELECT IS_IPV4('10.0.5.9'), IS_IPV4('10.0.5.256');
          -> 1, 0

  For a given argument, if IS_IPV4() returns 1, INET_ATON() (and INET6_ATON()) will return non-NULL. The converse statement is not true: In some cases, INET_ATON() returns non-NULL when IS_IPV4() returns 0.

  As implied by the preceding remarks, IS_IPV4() is more strict than INET_ATON() about what constitutes a valid IPv4 address, so it may be useful for applications that need to perform strong checks against invalid values. Alternatively, use INET6_ATON() to convert IPv4 addresses to internal form and check for a NULL result (which indicates an invalid address). INET6_ATON() is equally strong as IS_IPV4() about checking IPv4 addresses.

• IS_IPV4_COMPAT(expr)

  This function takes an IPv6 address represented in numeric form as a binary string, as returned by INET6_ATON(). It returns 1 if the argument is a valid IPv4-compatible IPv6 address, 0 otherwise. IPv4-compatible addresses have the form ::ipv4_address.

  mysql> SELECT IS_IPV4_COMPAT(INET6_ATON('::10.0.5.9'));
          -> 1
  mysql> SELECT IS_IPV4_COMPAT(INET6_ATON('::ffff:10.0.5.9'));
          -> 0

  The IPv4 part of an IPv4-compatible address can also be represented using hexadecimal notation. For example, 198.51.100.1 has this raw hexadecimal value:

  mysql> SELECT HEX(INET6_ATON('198.51.100.1'));
          -> 'C6336401'

  Expressed in IPv4-compatible form, ::198.51.100.1 is equivalent to ::c0a8:0001 or (without leading zeros) ::c0a8:1

  mysql> SELECT
      ->   IS_IPV4_COMPAT(INET6_ATON('::198.51.100.1')),
      ->   IS_IPV4_COMPAT(INET6_ATON('::c0a8:0001')),
      ->   IS_IPV4_COMPAT(INET6_ATON('::c0a8:1'));
          -> 1, 1, 1

• IS_IPV4_MAPPED(expr)

  This function takes an IPv6 address represented in numeric form as a binary string, as returned by INET6_ATON(). It returns 1 if the argument is a valid IPv4-mapped IPv6 address, 0 otherwise. IPv4-mapped addresses have the form ::ffff:ipv4_address.

  mysql> SELECT IS_IPV4_MAPPED(INET6_ATON('::10.0.5.9'));
          -> 0
  mysql> SELECT IS_IPV4_MAPPED(INET6_ATON('::ffff:10.0.5.9'));
          -> 1

  As with IS_IPV4_COMPAT() the IPv4 part of an IPv4-mapped address can also be represented using hexadecimal notation:

  mysql> SELECT
      ->   IS_IPV4_MAPPED(INET6_ATON('::ffff:198.51.100.1')),
      ->   IS_IPV4_MAPPED(INET6_ATON('::ffff:c0a8:0001')),
      ->   IS_IPV4_MAPPED(INET6_ATON('::ffff:c0a8:1'));
          -> 1, 1, 1

• IS_IPV6(expr)

  Returns 1 if the argument is a valid IPv6 address specified as a string, 0 otherwise. This function does not consider IPv4 addresses to be valid IPv6 addresses.

  mysql> SELECT IS_IPV6('10.0.5.9'), IS_IPV6('::1');
          -> 0, 1

  For a given argument, if IS_IPV6() returns 1, INET6_ATON() will return non-NULL.

• IS_UUID(string_uuid)

  Returns 1 if the argument is a valid string-format UUID, 0 if the argument is not a valid UUID, and NULL if the argument is NULL.

  “Valid” means that the value is in a format that can be parsed. That is, it has the correct length and contains only the permitted characters (hexadecimal digits in any lettercase and, optionally, dashes and curly braces). This format is most common:

  aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee

  These other formats are also permitted:

  aaaaaaaabbbbccccddddeeeeeeeeeeee
  {aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee}

  For the meanings of fields within the value, see the UUID() function description.

  mysql> SELECT IS_UUID('6ccd780c-baba-1026-9564-5b8c656024db');
  +-------------------------------------------------+
  | IS_UUID('6ccd780c-baba-1026-9564-5b8c656024db') |
  +-------------------------------------------------+
  |                                               1 |
  +-------------------------------------------------+
  mysql> SELECT IS_UUID('6CCD780C-BABA-1026-9564-5B8C656024DB');
  +-------------------------------------------------+
  | IS_UUID('6CCD780C-BABA-1026-9564-5B8C656024DB') |
  +-------------------------------------------------+
  |                                               1 |
  +-------------------------------------------------+
  mysql> SELECT IS_UUID('6ccd780cbaba102695645b8c656024db');
  +---------------------------------------------+
  | IS_UUID('6ccd780cbaba102695645b8c656024db') |
  +---------------------------------------------+
  |                                           1 |
  +---------------------------------------------+
  mysql> SELECT IS_UUID('{6ccd780c-baba-1026-9564-5b8c656024db}');
  +---------------------------------------------------+
  | IS_UUID('{6ccd780c-baba-1026-9564-5b8c656024db}') |
  +---------------------------------------------------+
  |                                                 1 |
  +---------------------------------------------------+
  mysql> SELECT IS_UUID('6ccd780c-baba-1026-9564-5b8c6560');
  +---------------------------------------------+
  | IS_UUID('6ccd780c-baba-1026-9564-5b8c6560') |
  +---------------------------------------------+
  |                                           0 |
  +---------------------------------------------+
  mysql> SELECT IS_UUID(RAND());
  +-----------------+
  | IS_UUID(RAND()) |
  +-----------------+
  |               0 |
  +-----------------+

• MASTER_POS_WAIT(log_name,log_pos[,timeout][,channel])

  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.

  On a multithreaded slave, the function waits until expiry of the limit set by the slave_checkpoint_group or slave_checkpoint_period system variable, when the checkpoint operation is called to update the status of the slave. Depending on the setting for the system variables, the function might therefore return some time after the specified position was reached.

  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.

  The optional channel value enables you to name which replication channel the function applies to. See Section 17.2.3, “Replication Channels” for more information.

  This function is unsafe for statement-based replication. A warning is logged if you use this function when binlog_format is set to STATEMENT.

• NAME_CONST(name,value)

  Returns the given value. When used to produce a result set column, NAME_CONST() causes the column to have the given name. The arguments should be constants.

  mysql> SELECT NAME_CONST('myname', 14);
  +--------+
  | myname |
  +--------+
  |     14 |
  +--------+

  This function is for internal use only. The server uses it when writing statements from stored programs that contain references to local program variables, as described in Section 24.7, “Binary Logging of Stored Programs”. You might see this function in the output from mysqlbinlog.

  For your applications, you can obtain exactly the same result as in the example just shown by using simple aliasing, like this:

  mysql> SELECT 14 AS myname;
  +--------+
  | myname |
  +--------+
  |     14 |
  +--------+
  1 row in set (0.00 sec)

  See Section 13.2.10, “SELECT Syntax”, for more information about column aliases.

• SLEEP(duration)

  Sleeps (pauses) for the number of seconds given by the duration argument, then returns 0. The duration may have a fractional part. If the argument is NULL or negative, SLEEP() produces a warning, or an error in strict SQL mode.

  When sleep returns normally (without interruption), it returns 0:

  mysql> SELECT SLEEP(1000);
  +-------------+
  | SLEEP(1000) |
  +-------------+
  |           0 |
  +-------------+

  When SLEEP() is the only thing invoked by a query that is interrupted, it returns 1 and the query itself returns no error. This is true whether the query is killed or times out:

  • This statement is interrupted using KILL QUERY from another session:

    mysql> SELECT SLEEP(1000);
    +-------------+
    | SLEEP(1000) |
    +-------------+
    |           1 |
    +-------------+

  • This statement is interrupted by timing out:

    mysql> SELECT /*+ MAX_EXECUTION_TIME(1) */ SLEEP(1000);
    +-------------+
    | SLEEP(1000) |
    +-------------+
    |           1 |
    +-------------+

  When SLEEP() is only part of a query that is interrupted, the query returns an error:

  • This statement is interrupted using KILL QUERY from another session:

    mysql> SELECT 1 FROM t1 WHERE SLEEP(1000);
    ERROR 1317 (70100): Query execution was interrupted

  • This statement is interrupted by timing out:

    mysql> SELECT /*+ MAX_EXECUTION_TIME(1000) */ 1 FROM t1 WHERE SLEEP(1000);
    ERROR 3024 (HY000): Query execution was interrupted, maximum statement
    execution time exceeded

  This function is unsafe for statement-based replication. A warning is logged if you use this function when binlog_format is set to STATEMENT.

• UUID()

  Returns a Universal Unique Identifier (UUID) generated according to RFC 4122, “A Universally Unique IDentifier (UUID) URN Namespace” (http://www.ietf.org/rfc/rfc4122.txt).

  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 devices not connected to each other.

  Warning

  Although UUID() values are intended to be unique, they are not necessarily unguessable or unpredictable. If unpredictability is required, UUID values should be generated some other way.

  UUID() returns a value that conforms to UUID version 1 as described in RFC 4122. The value is a 128-bit number represented as a utf8 string of five hexadecimal numbers in aaaaaaaa-bbbb-cccc-dddd-eeeeeeeeeeee format:

  • The first three numbers are generated from the low, middle, and high parts of a timestamp. The high part also includes the UUID version number.

  • 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 device has no Ethernet card, or it is unknown how to find the hardware address of an interface on the host operating system). In this case, spatial uniqueness cannot be guaranteed. Nevertheless, a collision should have very low probability.

    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-1026-9564-5b8c656024db'

  To convert between string and binary UUID values, use the UUID_TO_BIN() and BIN_TO_UUID() functions. To check whether a string is a valid UUID value, use the IS_UUID() function.

  Note

  UUID() does not work with statement-based replication.

• UUID_SHORT()

  Returns a “short” universal identifier as a 64-bit unsigned integer. Values returned by UUID_SHORT() differ from the string-format 128-bit identifiers returned by the UUID() function and have different uniqueness properties. The value of UUID_SHORT() is guaranteed to be unique if the following conditions hold:

  • The server_id value of the current server is between 0 and 255 and is unique among your set of master and slave servers

  • You do not set back the system time for your server host between mysqld restarts

  • You invoke UUID_SHORT() on average fewer than 16 million times per second between mysqld restarts

  The UUID_SHORT() return value is constructed this way:

    (server_id & 255) << 56
  + (server_startup_time_in_seconds << 24)
  + incremented_variable++;

  mysql> SELECT UUID_SHORT();
          -> 92395783831158784

  Note

  UUID_SHORT() does not work with statement-based replication.

• UUID_TO_BIN(string_uuid), UUID_TO_BIN(string_uuid, swap_flag)

  Converts a string UUID to a binary UUID and returns the result. (The IS_UUID() function description lists the permitted string UUID formats.) The return binary UUID is a VARBINARY(16) value. If the UUID argument is NULL, the return value is NULL. If any argument is invalid, an error occurs.

  UUID_TO_BIN() takes one or two arguments:

  • The one-argument form takes a string UUID value. The binary result is in the same order as the string argument.

  • The two-argument form takes a string UUID value and a flag value:

    • If swap_flag is 0, the two-argument form is equivalent to the one-argument form. The binary result is in the same order as the string argument.

    • If swap_flag is 1, the format of the return value differs: The time-low and time-high parts (the first and third groups of hexadecimal digits, respectively) are swapped. This moves the more rapidly varying part to the right and can improve indexing efficiency if the result is stored in an indexed column.

  Time-part swapping assumes the use of UUID version 1 values, such as are generated by the UUID() function. For UUID values produced by other means that do not follow version 1 format, time-part swapping provides no benefit. For details about version 1 format, see the UUID() function description.

  Suppose that you have the following string UUID value:

  mysql> SET @uuid = '6ccd780c-baba-1026-9564-5b8c656024db';

  To convert the string UUID to binary with or without time-part swapping, use UUID_TO_BIN():

  mysql> SELECT HEX(UUID_TO_BIN(@uuid));
  +----------------------------------+
  | HEX(UUID_TO_BIN(@uuid))          |
  +----------------------------------+
  | 6CCD780CBABA102695645B8C656024DB |
  +----------------------------------+
  mysql> SELECT HEX(UUID_TO_BIN(@uuid, 0));
  +----------------------------------+
  | HEX(UUID_TO_BIN(@uuid, 0))       |
  +----------------------------------+
  | 6CCD780CBABA102695645B8C656024DB |
  +----------------------------------+
  mysql> SELECT HEX(UUID_TO_BIN(@uuid, 1));
  +----------------------------------+
  | HEX(UUID_TO_BIN(@uuid, 1))       |
  +----------------------------------+
  | 1026BABA6CCD780C95645B8C656024DB |
  +----------------------------------+

  To convert a binary UUID returned by UUID_TO_BIN() to a string UUID, use BIN_TO_UUID(). If you produce a binary UUID by calling UUID_TO_BIN() with a second argument of 1 to swap time parts, you should also pass a second argument of 1 to BIN_TO_UUID() to unswap the time parts when converting the binary UUID back to a string UUID:

  mysql> SELECT BIN_TO_UUID(UUID_TO_BIN(@uuid));
  +--------------------------------------+
  | BIN_TO_UUID(UUID_TO_BIN(@uuid))      |
  +--------------------------------------+
  | 6ccd780c-baba-1026-9564-5b8c656024db |
  +--------------------------------------+
  mysql> SELECT BIN_TO_UUID(UUID_TO_BIN(@uuid,0),0);
  +--------------------------------------+
  | BIN_TO_UUID(UUID_TO_BIN(@uuid,0),0)  |
  +--------------------------------------+
  | 6ccd780c-baba-1026-9564-5b8c656024db |
  +--------------------------------------+
  mysql> SELECT BIN_TO_UUID(UUID_TO_BIN(@uuid,1),1);
  +--------------------------------------+
  | BIN_TO_UUID(UUID_TO_BIN(@uuid,1),1)  |
  +--------------------------------------+
  | 6ccd780c-baba-1026-9564-5b8c656024db |
  +--------------------------------------+

  If the use of time-part swapping is not the same for the conversion in both directions, the original UUID will not be recovered properly:

  mysql> SELECT BIN_TO_UUID(UUID_TO_BIN(@uuid,0),1);
  +--------------------------------------+
  | BIN_TO_UUID(UUID_TO_BIN(@uuid,0),1)  |
  +--------------------------------------+
  | baba1026-780c-6ccd-9564-5b8c656024db |
  +--------------------------------------+
  mysql> SELECT BIN_TO_UUID(UUID_TO_BIN(@uuid,1),0);
  +--------------------------------------+
  | BIN_TO_UUID(UUID_TO_BIN(@uuid,1),0)  |
  +--------------------------------------+
  | 1026baba-6ccd-780c-9564-5b8c656024db |
  +--------------------------------------+

• 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 13.2.6.2, “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);