Whether there are keywords in MySQL

mysql Is there a keyword in

This article mainly introduces “mysql Is there a keyword in ” Knowledge about , Xiaobian shows you the operation process through practical cases , The operation method is simple and fast , Practical , Hope this article “mysql Is there a keyword in ” The article can help you solve problems .

mysql There are keywords in .mysql A variety of keywords are provided in ：1、BETWEEN, Use in WHERE Query the range of time or number after the statement ;2、CALL, For calling stored procedures ;3、CURRENT_DATE, Get date of day ;4、CURRENT_TIME, Get the current time ;5、CURRENT_USER, return MYSQL Username ;6、CURSOR, For declaration mysql Cursor in ;7、DISTINCT, For de duplication .

The operating environment of this tutorial ：windows7 System 、mysql8 edition 、Dell G3 The computer .

In the use of MySQL When , Generally try to avoid using keywords as table names , For example, use keywords as table names , It needs to be written in a standard way SQL Statement plus []( or “) Distinguish between field names and table names .

The following is a list MySQL All keywords , Hope to use MySQL Our friends provide some reference help .

ADD	ALL	ALTER
ANALYZE	AND	AS
ASC	ASENSITIVE	BEFORE
BETWEEN	BIGINT	BINARY
BLOB	BOTH	BY
CALL	CASCADE	CASE
CHANGE	CHAR	CHARACTER
CHECK	COLLATE	COLUMN
CONDITION	CONNECTION	CONSTRAINT
CONTINUE	CONVERT	CREATE
CROSS	CURRENT_DATE	CURRENT_TIME
CURRENT_TIMESTAMP	CURRENT_USER	CURSOR
DATABASE	DATABASES	DAY_HOUR
DAY_MICROSECOND	DAY_MINUTE	DAY_SECOND
DEC	DECIMAL	DECLARE
DEFAULT	DELAYED	DELETE
DESC	DESCRIBE	DETERMINISTIC
DISTINCT	DISTINCTROW	p
DOUBLE	DROP	DUAL
EACH	ELSE	ELSEIF
ENCLOSED	ESCAPED	EXISTS
EXIT	EXPLAIN	FALSE
FETCH	FLOAT	FLOAT4
FLOAT8	FOR	FORCE
FOREIGN	FROM	FULLTEXT
GOTO	GRANT	GROUP
HAVING	HIGH_PRIORITY	HOUR_MICROSECOND
HOUR_MINUTE	HOUR_SECOND	IF
IGNORE	IN	INDEX
INFILE	INNER	INOUT
INSENSITIVE	INSERT	INT
INT1	INT2	INT3
INT4	INT8	INTEGER
INTERVAL	INTO	IS
ITERATE	JOIN	KEY
KEYS	KILL	LABEL
LEADING	LEAVE	LEFT
LIKE	LIMIT	LINEAR
LINES	LOAD	LOCALTIME
LOCALTIMESTAMP	LOCK	LONG
LONGBLOB	LONGTEXT	LOOP
LOW_PRIORITY	MATCH	MEDIUMBLOB
MEDIUMINT	MEDIUMTEXT	MIDDLEINT
MINUTE_MICROSECOND	MINUTE_SECOND	MOD
MODIFIES	NATURAL	NOT
NO_WRITE_TO_BINLOG	NULL	NUMERIC
ON	OPTIMIZE	OPTION
OPTIONALLY	OR	ORDER
OUT	OUTER	OUTFILE
PRECISION	PRIMARY	PROCEDURE
PURGE	RAID0	RANGE
READ	READS	REAL
REFERENCES	REGEXP	RELEASE
RENAME	REPEAT	REPLACE
REQUIRE	RESTRICT	RETURN
REVOKE	RIGHT	RLIKE
SCHEMA	SCHEMAS	SECOND_MICROSECOND
SELECT	SENSITIVE	SEPARATOR
SET	SHOW	SMALLINT
SPATIAL	SPECIFIC	SQL
SQLEXCEPTION	SQLSTATE	SQLWARNING
SQL_BIG_RESULT	SQL_CALC_FOUND_ROWS	SQL_SMALL_RESULT
SSL	STARTING	STRAIGHT_JOIN
TABLE	TERMINATED	THEN
TINYBLOB	TINYINT	TINYTEXT
TO	TRAILING	TRIGGER
TRUE	UNDO	UNION
UNIQUE	UNLOCK	UNSIGNED
UPDATE	USAGE	USE
USING	UTC_DATE	UTC_TIME
UTC_TIMESTAMP	VALUES	VARBINARY
VARCHAR	VARCHARACTER	VARYING
WHEN	WHERE	WHILE
WITH	WRITE	X509
XOR	YEAR_MONTH	ZEROFILL

Here is a list of common mysql The role of keywords

keyword	effect
ANALYZE	adopt Analyze Table The index statement can be repaired . Use “SHOW INDEX FROM Table name ” View the index status in the table , When the number of different values in the field is much more than that in the table CARDINALITY In quantity , The index basically doesn't work , Use this time “ANALYZE TABLE Table name ” The index can be repaired , Again using “SHOW INDEX FROM Table name ” You can see CARDINALITY Index returned to normal
BETWEEN	Use in WHERE Later time or number range query , Such as “SELECT * FROM USER WHERE CREATE BETWEEN '2020-11-20' AND '2020-11-30';” The query is 20 No. to 30 Data between numbers , If the time type is DATETIME The query range is 00:00:00, For example, in the above query statement, if CREATE_TIME by DATETIME type , The scope of the query is “2020-11-20 00:00:00 to 2020-11-30 00:00:00”
CALL	For calling stored procedures , Such as ：CALL showUser()
CASCADE	Add after constraint , After setting, delete 、 When the master table is updated, the slave table will also be operated , for example ：“ CONSTRAINT ' User information ' FOREIGN KEY (USER_NAME) REFERENCES TASK.USER (NAME) ON DELETE CASCADE ON UPDATE CASCADE”, After adding, when the user table changes the user name , The user name from the table will also be modified
CURRENT_DATE	Used to get the date of the day , Such as “SELECT CURRENT_DATE” Returns the date of the day
CURRENT_TIME	Used to get the current time , Such as "SELECT CURRENT_TIME" Returns the current hour, minute and second
DEFAULT CURRENT_TIMESTAMP	When creating a time field, if you add this code, it means that the current time is inserted by default when adding data , When creating a field ：“ create_time timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP”
ON UPDATE CURRENT_TIMESTAMP	If you add this code when creating a time field, it means that the current time will be synchronized by default when modifying data , When creating a field ：“update_time timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP”
CURRENT_USER	return MYSQL Username
CURSOR	For declaration mysql Cursor in , Used in stored procedures , It acts as a pointer , usage ：“DECLARE Cursor name CURSOR FRO The result set of the query ”
DECLARE	Used to declare variables in compound statements , For example, in a stored procedure , have access to SET Variable name = value Reassign in this way , The result in the example is 1 yes “ test ”, result 1(2) yes “ test 1”
DELAYED	Used to use deferred insert operations , In execution DELAYED When a statement is declared , The database will first return status information , Then put the insert operation into the queue , Wait for instructions that do not operate on the queue data to start executing the queue
DESCRIBE	Used to view the detailed design of fields in the data table , There are two uses ：1.DESCRIBE Table name View all fields .2.DESCRIBE Table name Field name Used to view fields individually
DISTINCT	Remove duplicate data , Only de duplicated data can be returned , Must be in the first field of the query , It is often used to query how many pieces of data in a field are not repeated . Such as SELECT COUNT(DISTINCT name) FROM user
DISTINCTROW	De duplication for join table query , You can query the attached table data associated with the main table instead of the data not related to the queried main table , Such as SELECT DISTINCTROW user.id ,untitled.friend_name FROM user INNER JOIN untitled ON user.id = untitled.friend_id WHERE user.id = '1'; Users can be queried id Associated with untitled The names of friends in the table , Do not include friends of users who have no query
DROP	It is mainly used to delete the structure , Such as deleting database ：DROP DATABASE Database name , Delete table ：DROP TABLE Table name , Delete field ：ALTER TABLE Table name DROP Field name
DUAL	Virtual table in mysql5.1 The above version will have , It feels like ORACLE That's what works , Because in ORACLE Queries used in must have FROM Table name , And in the mysql No error will be reported if there is no table name in the , If in mysql in SELECT 1+1 No problem, but in ORACLE China will report an error , You need to use it at this time SELECT 1+1 FROM DUAL, official declaration ：DUAL It's entirely for the convenience of those who require all SELECT Every statement should have FROM or other People who love you
EXISTS	Used in WHERE Post judgment operation , The return result is a Boolean value , The usage method is to substitute the existing row into the query to check , If one or more rows of data are returned in the internal query , Then output the data of this line , On the contrary, if there is no data in the internal query, the data of this line will not be output , Such as ：SELECT * FROM user u WHERE EXISTS(SELECT * FROM untitled n WHERE n.friend_id=u.id) What's back is untitled In the table friend Fields can be associated with user In the table id Associated data , It can also be in EXISTS Keyword prefix NOT All that is returned is irrelevant data
EXPLAIN	Use to view a sql Implementation , Whether the index is added or whether the full table scan is done , Usage mode ： stay SELECT with , Such as EXPLAIN SELECT * FROM user
FULLTEXT	Full-text index , Used to optimize query speed , You can add... When creating a table FULLTEXT( Field 1, Field 2), You can also add... After creating the table ALTER TABLE Table name ADD FULLTEXT INDEX Index name ( Field name ) It should be noted that adding an index is , The table engine should use MyISAM Otherwise, it will report a mistake The used table type doesn't support FULLTEXT indexes
GRANT	Used for user permission operations , You can grant or delete user permissions , There are many ways to operate, such as ：CREATE USER 'testUser'@'host' IDENTIFIED BY '123456'; Used to create users ,show grants for 'testUser'@'host'; View user permissions and other operations
GROUP	For grouping operations ,GROUP BY Field name The fields to be queried after grouping must be in GROUP BY The error will be reported after adding , More classic usage, such as ：SELECT friend_name , COUNT(friend_name) FROM untitled GROUP BY friend_name Query the number of data pieces of a certain type
HAVING	Used to filter data after aggregation , And WHERE The difference is that ,WHERE It is used to filter data before aggregation. Aggregation functions such as COUNT,SUM etc. ,HAVING It is filtered after aggregation. You can use the aggregation function , for example ：SELECT friend_name , COUNT(friend_name) FROM untitled GROUP BY friend_name HAVING COUNT(friend_name) >1 The query is friend_name The number of data pieces greater than one
HIGH_PRIORITY	be used for SELECT and INSERT sentence , Declare this operation as a high priority operation , The database will perform such operations first , Such as ：SELECT HIGH_PRIORITY * FROM user When there are multiple operations at the same time , This statement takes precedence
IGNORE	It is often used to ignore error data during batch insertion , Such as ：INSERT IGNORE INTO user (id,name,age) values(6,'pangqi',25); If the primary key id If it already exists, no error will be reported , Instead, perform the next insertion operation
INNER	Used for internal connection query , Set up ON After the conditions are met, all the qualified data will be displayed , Connect to the left , The difference between right connections is ：INNER No focus ,mysql Will find out all the data that meet the conditions , So be careful not to appear Cartesian product when using , In addition, due to INNER yes mysql Default connection mode , So you can omit INNER Keywords such as ：SELECT * FROM user JOIN untitled ON user.id = untitled.friend_id
INTERVAL	Mainly used for time interval , Such as ：SELECT * FROM USER where create_time < NOW()-INTERVAL 4 DAY The data returned is the data created four days ago , Can also be DAY Replace with hours , minute , Year, month, etc , It can also be used to compare data, such as ：SELECT INTERVAL(6,1,2,3,4,7,8,9,10) Returns the 4, Because in comparison mysql Can be indexed as 0 To compare the next data , When the next data is larger than the index is 0 When the data is ,mysql The index of the previous data will be returned
IS	mysql Medium IS Keywords are only used in IS NULL or IS NOT NULL in Such as ：SELECT * FROM USER where update_time IS NULL
JOIN	Used to connect two tables , The connection mode is generally internal connection INNER JOIN, The right connection RIGHT JOIN, Left connection LEFT JOIN
KEY	KEY It's the physical structure of the database , There are two levels of meaning and function ：1： constraint ,2： Indexes , Such as the declaration of primary key PRIMARY KEY (id),, There will be unique constraints , The index will be automatically added again
KILL	Used to terminate mysql Thread in , have access to SHOW PROCESSLIST View the thread currently in progress , Use KILL Threads id Thread termination , There are two modifiers 1：CONNECTION The default modifier can terminate all connections with the thread id Related links ,2：QUERY Terminate the statement now executed , But the connection will not be terminated
LABEL	Statement tags
LEAVE	Leave Statement to exit the process control statement block of the specified label , Usually used in begin…end, as well as loop, repeat, while In the loop statement of , It's like... In programming break equally , Usage mode LEAVE Circular name ;
LEFT	LEFT() The function is a string function , It returns the left part of a string of a specified length . Such as ：SELECT LEFT(name,3) FROM user
LIKE	For fuzzy search , Collocation % And _ The common use ,% Represents a query for one or more wildcards , and _ Represents a character , Such as ：SELECT * FROM user WHERE name LIKE '%i' You can find all name China and Israel i Data at the end , take % Switch to _ after , The query condition becomes a query name China and Israel i Data that ends with only one character in front
LIMIT	Used for paging queries , Such as :SELECT * FROM user LIMIT 4,5 The first parameter is the starting number As the above example, it starts from 4 Bar data starts to return , The second parameter is offset, as shown in the above example. The parameter is 5 Then it means to return from 4 Back of bar 5 Data , The previous offset can be -1 Represents all data after the initial number of queries , But this writing is mysql Officially considered a mistake , So the newer version mysql It doesn't work , The best way is to give a larger number
LOCALTIME	Local time , It can be used as a query result field ,where Conditions , When inserting the current time , Update time, etc ,mysql There are many time functions , You can choose different functions to use according to your needs , example ：SELECT LOCALTIME,NOW(),sysdate(), localtimestamp, localtimestamp();
LOCK	Lock table and unlock MySQL Enables client sessions to explicitly acquire table locks , To access the table in collaboration with other sessions , Or prevent other sessions from modifying the table when the session needs mutually exclusive access . A session can only acquire or release locks for itself . One session cannot acquire the lock of another session , You can't release the lock that another conversation holds . example ：LOCK table user read local A lock table operation will be generated , All operations to modify the table will be rejected and prompted ：Table 'user' was locked with a READ lock and can't be updated, have access to unlock tables; Keyword unlock
LOW_PRIORITY	Low priority ,MySQL Allows you to change the priority of statement scheduling , It enables better collaboration of queries from multiple clients , In this way, a single client will not wait for a long time due to locking . Commonly used in DELETE、INSERT、LOAD DATA、REPLACE and UPDATE In the sentence , example ：update LOW_PRIORITY user set username = 'zhangsan' under these circumstances , If the writer is waiting , The second reader arrived , Then allow the second reader to plug in before the writer . Only when there are no other readers , The writer is allowed to start the operation .
MOD	Take the cofunction , Such as ：select mod(12,5) Returns the remainder 2
NATURAL	Natural join , yes JOIN A kind of , It is characterized by automatic record matching of fields with the same name in the table , These fields with the same name can be of different types , Therefore, the types of fields in the table can be different , It can be applied to INNER ,LEFT etc. JOIN in , example ：select * from user NATURAL LEFT JOIN user2 ad locum user And user2 The difference is except id outside user2 The field will be followed by 1, This will result in automatic use when connecting id Association , And so it turns out
OPTIMIZE	effect ： Optimize the defragmentation and index of the table , When the database stores data, the database allocates table space , And index the data. When the data is deleted, the database will not recover these resources, but wait for new data to fill these gaps , Use OPTIMIZE Keywords can actively clear these occupied resources , usage ：optimize table The name of the table
RANGE	Partition ： Based on a given interval range , The value of this field in a given interval is required to be continuous , When the operation is performed, the corresponding partition will be taken , Can greatly improve efficiency , The requirement is that if the table has a primary key, the partition field should also be in the row and column of the primary key , usage ： Create table statement +PARTITION BY RANGE (xuehao) (PARTITION p0 VALUES LESS THAN (6),PARTITION p1 VALUES LESS THAN (11),PARTITION p2 VALUES LESS THAN (16), PARTITION p3 VALUES LESS THAN (21));
REFERENCES	Establish foreign key relationship , In the statement of creating a table ：FOREIGN KEY(uid) REFERENCES users(id) It means the field uid Will and user The primary key field of the table id Connect
REGEXP	Regular expressions , You can use regular expressions in conditions , Use SELECT * FROM user WHERE email NOT REGEXP'^[A-Z0-9._%-][email protected][A-Z0-9.-]+.[A-Z]{2,4}$'
RENAME	Modify table name , Use ：rename table user2 to user3;
REPEAT	Copy the given data as a string for a specified number of times, such as ：select REPEAT(3,3) The result is “333”
REPLACE	Replace all specified strings , Such as ：select REPLACE(' This is a string , Or a character ',' One ',' Two ');
REVOKE	Revocation has been given to MySQL User permissions , Such as ：revoke all on *.* from [email protected]; Remember to refresh the user permission table after completion FLUSH PRIVILEGES;
RIGHT	Truncate the string , Such as ：select RIGHT(' This is a string ',5), The string of specified digits will be intercepted in reverse order
RLIKE	Fuzzy query , And like When it's different ,rlike The content of can be regular , And may not exactly match , Such as ：select * from user where email RLIKE '^www.*$';
SEPARATOR	The query result can be changed into one line by string connection ,SEPARATOR Specify connector , Need to cooperate GROUP BY Use , Such as ：SELECT *, GROUP_CONCAT(username order by username separator ';') SCORE FROM user GROUP BY email RLIKE '^www.*$'
USING	When connecting queries, if the field names are the same, they can be used as connection conditions ,using Can replace on Appear as ：select * from user left join students USING(quanxian)
WHILE	Circular statement keyword , Used in stored procedures , It needs to be used in combination with process control statements , Such as ：CREATE PROCEDURE fun() BEGIN SET @sum:=10; WHILE @sum > 0 DO SELECT @sum; SET @sum:[email protected]; END WHILE; END CALL fun(); DROP PROCEDURE fun
XOR	Express logical XOR , When any one of the operands is NULL when , The return value is NULL, For non NULL The number of operations , If two logical true and false values are different , Then the returned result is 1, Otherwise 0, Such as ：select true XOR null;select true XOR true;select true XOR false;
ZEROFILL	When creating a table, add this keyword to the numeric type , If the number of inserted digits is insufficient, the corresponding number of digits will be filled automatically , Such as ：CREATE TABLE student3 ( id int(11) unsigned zerofill not null, xuehao int(50) NOT NULL );insert into student3 value(1,2); select * from student3;

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