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5.2.5. The Server SQL Mode
The MySQL server can operate in different SQL modes, and can
apply these modes differently for different clients. This
capability enables each application to tailor the server's
operating mode to its own requirements.
Modes define what SQL syntax MySQL should support and what
kind of data validation checks it should perform. This makes
it easier to use MySQL in different environments and to use
MySQL together with other database servers.
You can set the default SQL mode by starting
mysqld with the
--sql-mode="modes "
option. modes is a list of
different modes separated by comma
(‘, ’) characters. The default
value is empty (no modes set). The
modes value also can be empty
(--sql-mode="" ) if you want to clear it
explicitly.
You can change the SQL mode at runtime by using a SET
[GLOBAL|SESSION]
sql_mode='modes '
statement to set the sql_mode system value.
Setting the GLOBAL variable requires the
SUPER privilege and affects the operation
of all clients that connect from that time on. Setting the
SESSION variable affects only the current
client. Any client can change its own session
sql_mode value at any time.
You can retrieve the current global or session
sql_mode value with the following
statements:
SELECT @@global.sql_mode;
SELECT @@session.sql_mode;
The most important sql_mode values are
probably these:
-
ANSI
Change syntax and behavior to be more conformant to
standard SQL.
-
STRICT_TRANS_TABLES
If a value could not be inserted as given into a
transactional table, abort the statement. For a
non-transactional table, abort the statement if the value
occurs in a single-row statement or the first row of a
multiple-row statement. More detail is given later in this
section.
-
TRADITIONAL
Make MySQL behave like a “traditional” SQL
database system. A simple description of this mode is
“give an error instead of a warning” when
inserting an incorrect value into a column.
Note: The
INSERT /UPDATE aborts
as soon as the error is noticed. This may not be what you
want if you are using a non-transactional storage engine,
because data changes made prior to the error are not be
rolled back, resulting in a “partially done”
update.
When this manual refers to “strict mode,” it
means a mode where at least one of
STRICT_TRANS_TABLES or
STRICT_ALL_TABLES is enabled.
The following list describes all supported modes:
-
ALLOW_INVALID_DATES
Don't do full checking of dates. Check only that the month
is in the range from 1 to 12 and the day is in the range
from 1 to 31. This is very convenient for Web applications
where you obtain year, month, and day in three different
fields and you want to store exactly what the user
inserted (without date validation). This mode applies to
DATE and DATETIME
columns. It does not apply TIMESTAMP
columns, which always require a valid date.
The server requires that month and day values be legal,
and not merely in the range 1 to 12 and 1 to 31,
respectively. With strict mode disabled, invalid dates
such as '2004-04-31' are converted to
'0000-00-00' and a warning is
generated. With strict mode enabled, invalid dates
generate an error. To allow such dates, enable
ALLOW_INVALID_DATES .
-
ANSI_QUOTES
Treat ‘" ’ as an identifier
quote character (like the
‘` ’ quote character) and
not as a string quote character. You can still use
‘` ’ to quote identifiers
with this mode enabled. With
ANSI_QUOTES enabled, you cannot use
double quotes to quote a literal string, because it is
interpreted as an identifier.
-
ERROR_FOR_DIVISION_BY_ZERO
Produce an error in strict mode (otherwise a warning) when
we encounter a division by zero (or
MOD(X,0) ) during an
INSERT or UPDATE . If
this mode is not enabled, MySQL instead returns
NULL for divisions by zero. If used in
INSERT IGNORE or UPDATE
IGNORE , MySQL generates a warning for divisions
by zero, but the result of the operation is
NULL .
-
HIGH_NOT_PRECEDENCE
The precedence of the NOT operator is
such that expressions such as NOT a BETWEEN b AND
c are parsed as NOT (a BETWEEN b AND
c) . In some older versions of MySQL, the
expression was parsed as (NOT a) BETWEEN b AND
c . The old higher-precedence behavior can be
obtained by enabling the
HIGH_NOT_PRECEDENCE SQL mode.
mysql> SET sql_mode = '';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
-> 0
mysql> SET sql_mode = 'broken_not';
mysql> SELECT NOT 1 BETWEEN -5 AND 5;
-> 1
-
IGNORE_SPACE
Allow spaces between a function name and the
‘( ’ character. This forces
all function names to be treated as reserved words. As a
result, if you want to access any database, table, or
column name that is a reserved word, you must quote it.
For example, because there is a USER()
function, the name of the user table in
the mysql database and the
User column in that table become
reserved, so you must quote them:
SELECT "User" FROM mysql."user";
The IGNORE_SPACE SQL mode applies to
built-in functions, not to stored routines. it is always
allowable to have spaces after a routine name, regardless
of whether IGNORE_SPACE is enabled.
-
NO_AUTO_CREATE_USER
Prevent GRANT from automatically
creating new users if it would otherwise do so, unless a
non-empty password also is specified.
-
NO_AUTO_VALUE_ON_ZERO
NO_AUTO_VALUE_ON_ZERO affects handling
of AUTO_INCREMENT columns. Normally,
you generate the next sequence number for the column by
inserting either NULL or
0 into it.
NO_AUTO_VALUE_ON_ZERO suppresses this
behavior for 0 so that only
NULL generates the next sequence
number.
This mode can be useful if 0 has been
stored in a table's AUTO_INCREMENT
column. (Storing 0 is not a recommended
practice, by the way.) For example, if you dump the table
with mysqldump and then reload it,
MySQL normally generates new sequence numbers when it
encounters the 0 values, resulting in a
table with contents different from the one that was
dumped. Enabling NO_AUTO_VALUE_ON_ZERO
before reloading the dump file solves this problem.
mysqldump now automatically includes in
its output a statement that enables
NO_AUTO_VALUE_ON_ZERO , to avoid this
problem.
-
NO_BACKSLASH_ESCAPES
Disable the use of the backslash character
(‘\ ’) as an escape
character within strings. With this mode enabled,
backslash becomes any ordinary character like any other.
-
NO_DIR_IN_CREATE
When creating a table, ignore all INDEX
DIRECTORY and DATA DIRECTORY
directives. This option is useful on slave replication
servers.
-
NO_ENGINE_SUBSTITUTION
Prevents automatic substitution of the default storage
engine when a statement such as CREATE
TABLE specifies a storage engine that is
disabled or not compiled in.
-
NO_FIELD_OPTIONS
Do not print MySQL-specific column options in the output
of SHOW CREATE TABLE . This mode is used
by mysqldump in portability mode.
-
NO_KEY_OPTIONS
Do not print MySQL-specific index options in the output of
SHOW CREATE TABLE . This mode is used by
mysqldump in portability mode.
-
NO_TABLE_OPTIONS
Do not print MySQL-specific table options (such as
ENGINE ) in the output of SHOW
CREATE TABLE . This mode is used by
mysqldump in portability mode.
-
NO_UNSIGNED_SUBTRACTION
In subtraction operations, do not mark the result as
UNSIGNED if one of the operands is
unsigned. Note that this makes BIGINT
UNSIGNED not 100% usable in all contexts. See
Section 12.8, “Cast Functions and Operators”.
-
NO_ZERO_DATE
In strict mode, don't allow
'0000-00-00' as a valid date. You can
still insert zero dates with the IGNORE
option. When not in strict mode, the date is accepted but
a warning is generated.
-
NO_ZERO_IN_DATE
In strict mode, don't accept dates where the month or day
part is 0. If used with the IGNORE
option, MySQL inserts a '0000-00-00'
date for any such date. When not in strict mode, the date
is accepted but a warning is generated.
-
ONLY_FULL_GROUP_BY
Do not allow queries for which the GROUP
BY clause refers to a column that is not present
in the output column list.
-
PIPES_AS_CONCAT
Treat || as a string concatenation
operator (same as CONCAT() ) rather than
as a synonym for OR .
-
REAL_AS_FLOAT
Treat REAL as a synonym for
FLOAT . By default, MySQL treats
REAL as a synonym for
DOUBLE .
-
STRICT_ALL_TABLES
Enable strict mode for all storage engines. Invalid data
values are rejected. Additional detail follows.
-
STRICT_TRANS_TABLES
Enable strict mode for transactional storage engines, and
when possible for non-transactional storage engines.
Additional details follow.
Strict mode controls how MySQL handles input values that are
invalid or missing. A value can be invalid for several
reasons. For example, it might have the wrong data type for
the column, or it might be out of range. A value is missing
when a new row to be inserted does not contain a value for a
column that has no explicit DEFAULT clause
in its definition.
For transactional tables, an error occurs for invalid or
missing values in a statement when either of the
STRICT_ALL_TABLES or
STRICT_TRANS_TABLES modes are enabled. The
statement is aborted and rolled back.
For non-transactional tables, the behavior is the same for
either mode, if the bad value occurs in the first row to be
inserted or updated. The statement is aborted and the table
remains unchanged. If the statement inserts or modifies
multiple rows and the bad value occurs in the second or later
row, the result depends on which strict option is enabled:
For STRICT_ALL_TABLES , MySQL returns an
error and ignores the rest of the rows. However, in this
case, the earlier rows still have been inserted or
updated. This means that you might get a partial update,
which might not be what you want. To avoid this, it's best
to use single-row statements because these can be aborted
without changing the table.
For STRICT_TRANS_TABLES , MySQL converts
an invalid value to the closest valid value for the column
and insert the adjusted value. If a value is missing,
MySQL inserts the implicit default value for the column
data type. In either case, MySQL generates a warning
rather than an error and continues processing the
statement. Implicit defaults are described in
Section 11.1.4, “Data Type Default Values”.
Strict mode disallows invalid date values such as
'2004-04-31' . It does not disallow dates
with zero parts such as '2004-04-00' or
“zero” dates. To disallow these as well, enable
the NO_ZERO_IN_DATE and
NO_ZERO_DATE SQL modes in addition to
strict mode.
If you are not using strict mode (that is, neither
STRICT_TRANS_TABLES nor
STRICT_ALL_TABLES is enabled), MySQL
inserts adjusted values for invalid or missing values and
produces warnings. In strict mode, you can produce this
behavior by using INSERT IGNORE or
UPDATE IGNORE . See
Section 13.5.4.28, “SHOW WARNINGS Syntax”.
The following special modes are provided as shorthand for
combinations of mode values from the preceding list.
The descriptions include all mode values that are available in
the most recent version of MySQL. For older versions, a
combination mode does not include individual mode values that
are not available except in newer versions.
-
ANSI
Equivalent to REAL_AS_FLOAT ,
PIPES_AS_CONCAT ,
ANSI_QUOTES ,
IGNORE_SPACE . See
Section 1.9.3, “Running MySQL in ANSI Mode”.
-
DB2
Equivalent to PIPES_AS_CONCAT ,
ANSI_QUOTES ,
IGNORE_SPACE ,
NO_KEY_OPTIONS ,
NO_TABLE_OPTIONS ,
NO_FIELD_OPTIONS .
-
MAXDB
Equivalent to PIPES_AS_CONCAT ,
ANSI_QUOTES ,
IGNORE_SPACE ,
NO_KEY_OPTIONS ,
NO_TABLE_OPTIONS ,
NO_FIELD_OPTIONS ,
NO_AUTO_CREATE_USER .
-
MSSQL
Equivalent to PIPES_AS_CONCAT ,
ANSI_QUOTES ,
IGNORE_SPACE ,
NO_KEY_OPTIONS ,
NO_TABLE_OPTIONS ,
NO_FIELD_OPTIONS .
-
MYSQL323
Equivalent to NO_FIELD_OPTIONS ,
HIGH_NOT_PRECEDENCE .
-
MYSQL40
Equivalent to NO_FIELD_OPTIONS ,
HIGH_NOT_PRECEDENCE .
-
ORACLE
Equivalent to PIPES_AS_CONCAT ,
ANSI_QUOTES ,
IGNORE_SPACE ,
NO_KEY_OPTIONS ,
NO_TABLE_OPTIONS ,
NO_FIELD_OPTIONS ,
NO_AUTO_CREATE_USER .
-
POSTGRESQL
Equivalent to PIPES_AS_CONCAT ,
ANSI_QUOTES ,
IGNORE_SPACE ,
NO_KEY_OPTIONS ,
NO_TABLE_OPTIONS ,
NO_FIELD_OPTIONS .
-
TRADITIONAL
Equivalent to STRICT_TRANS_TABLES ,
STRICT_ALL_TABLES ,
NO_ZERO_IN_DATE ,
NO_ZERO_DATE ,
ERROR_FOR_DIVISION_BY_ZERO ,
NO_AUTO_CREATE_USER .
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