There are keywords in mysql. Mysql provides a variety of keywords: 1. BETWEEN, used to query the time or number range after the WHERE statement; 2. CALL, used to call stored procedures; 3. CURRENT_DATE, to get the current date; 4. CURRENT_TIME, to get the current date Time; 5. CURRENT_USER, returns the user name of MYSQL; 6. CURSOR, used to declare the cursor in mysql; 7. DISTINCT, used to remove duplicate data.
The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.
When using MySQL, generally try to avoid using keywords as table names. If you use keywords as table names, you need to add [] (or ") to the SQL statement according to standard writing to distinguish the field name and table name. .
All MySQL keywords are listed below, hoping to provide some reference help for friends who use MySQL.
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 |
The following is a list of the functions of common mysql keywords
Keyword | Function |
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Through the Analyze Table statement The index can be repaired. Use " | SHOW INDEX FROM table name" to view the index status in the table. When the number of different values in the field is much greater than the number of CARDINALITY in the table, the index basically has no effect. In this case, use " ANALYZE TABLE table name" can repair the index. Use " SHOW INDEX FROM table name" again to see that the CARDINALITY index returns to normal
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Use the time or number range query after WHERE, such as " | SELECT * FROM USER WHERE CREATE BETWEEN '2020-11-20' AND '2020-11-30';" The query is For data between the 20th and the 30th, if the time type is DATETIME, the query range is 00:00:00. For example, in the above query statement, if CREATE_TIME is of DATETIME type, the query range is " 2020-11-20 00:00:00 to 2020-11-30 00:00:00”
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is used to call stored procedures, such as: | CALL showUser()
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is added after the constraint. After setting, the slave table will also be operated when the master table is deleted or updated, for example: " | CONSTRAINT 'User information' FOREIGN KEY (USER_NAME) REFERENCES TASK.USER (NAME) ON DELETE CASCADE ON UPDATE CASCADE", after adding, when the user name is modified in the user table, the user name in the slave table will also be modified.
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is used to obtain today’s date. For example, “ | SELECT CURRENT_DATE” returns today’s date
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is used to obtain the current time. For example, " | SELECT CURRENT_TIME" returns the current hours, minutes and seconds.
| ##DEFAULT CURRENT_TIMESTAMP
create_time timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP | "
| ON UPDATE CURRENT_TIMESTAMP
update_time timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP | ”
| CURRENT_USER
CURSOR | |
DECLARE cursor name CURSOR FRO query result set | "
| DECLARE
SET variable name = value | to reassign the value. In the example, result 1 is "test", result 1 ( 2) It is "Test 1"
| DELAYED
DESCRIBE | |
DESCRIBE table name | View all fields.2.|
DISTINCT | removes duplicate data, and only deduplicated data can be returned. It must be the first field in the query. It is often used to query how many unique pieces of data there are in a certain field.For example, SELECT COUNT(DISTINCT name) FROM user
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DISTINCTROW | is used to deduplicate joint table queries, and you can query the associations in the main table The appendix data does not include data that is not related to the main table queried, such as SELECT DISTINCTROW user.id, untitled.friend_name FROM user INNER JOIN untitled ON user.id = untitled.friend_id WHERE user.id = '1'; You can query the user ID and the friend names in the associated untitled table, excluding the friends of the user who is not queried |
DROP | Mainly used to delete structures, such as deleting database: DROP DATABASE database name , deleting table: DROP TABLE table name , deleting fields: ALTER TABLE table name DROP field name
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DUAL | Virtual tables are available in mysql5.1 or above. I feel that they are only useful in ORACLE because the FROM table is required to use queries in ORACLE. name, but if there is no table name in mysql, no error will be reported. For example, in mysql, SELECT 1 1 will not cause a problem, but in ORACLE, an error will be reported. In this case, use SELECT 1 1 FROM DUAL , official statement: DUAL is entirely for the convenience of those who require that all SELECT statements should have FROM or other clauses
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EXISTS | Used for judgment operation after WHERE. The return result is a Boolean value. The method of use is to substitute the existing rows into the inner query for verification. If one or more rows of data are returned in the inner query, the data of this row will be output, and vice versa. If there is no data in the query, the data of this row will not be output, such as: SELECT * FROM user u WHERE EXISTS(SELECT * FROM untitled n WHERE n.friend_id=u.id) What is returned is the friend field in the untitled table. For data associated with the id in the user table, you can also add NOT in front of the EXISTS keyword to return unrelated data. |
EXPLAIN | Use to view one SQL execution, whether indexes are added or full table scans are performed, etc. How to use: add before SELECT, such as EXPLAIN SELECT * FROM user
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FULLTEXT | Full-text index is used to optimize query speed. You can add FULLTEXT(Field 1, Field 2) when creating the table, or you can add ALTER separately after creating the table. TABLE table name ADD FULLTEXT INDEX index name ( field name) It should be noted that when adding an index, the table engine must use MyISAM, otherwise an error will be reportedThe used table type doesn't support FULLTEXT indexes
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GRANT | is used for user permission operations. It can grant user permissions or delete user permissions. There are many operation methods, 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 | is used for grouping operations, GROUP BY field name The fields to be queried after grouping operations must be added after GROUP BY otherwise an error will be reported. The more classic usage is as follows :SELECT friend_name , COUNT(friend_name) FROM untitled GROUP BY friend_name Query the number of data items of a certain type |
HAVING | Used in aggregation Then filter the data. The difference from WHERE is that WHERE filters the data before aggregation and cannot use aggregate functions such as COUNT, SUM, etc. HAVING filters the data after aggregation and you can use aggregate functions, for example: SELECT friend_name , COUNT(friend_name) FROM untitled GROUP BY friend_name HAVING COUNT(friend_name) >1 The query is the number of data items with friend_name greater than one |
HIGH_PRIORITY | Used for SELECT and INSERT statements to 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. implement |
IGNORE | is often used to ignore error data when inserting in batches, such as: INSERT IGNORE INTO user (id,name,age) values(6,'pangqi',25); If the primary key id already exists, no error will be reported, but the next insertion operation will be performed. |
INNER | is used for inner connection query. After setting the ON condition, it will Display all the data that meets the conditions. The difference from left join and right join is that INNER has no focus. MySQL will find all the data that meets the conditions, so be careful not to have a Cartesian product when using it. In addition, because INNER is the default connection method of mysql, so you can omit the INNER keyword such as: SELECT * FROM user JOIN untitled ON user.id = untitled.friend_id
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INTERVAL | Mainly used for time intervals, such as: SELECT * FROM USER where create_time < NOW()-INTERVAL 4 DAY returns the data created four days ago, or DAY can be Replace with hours, minutes, years, months, etc., and can also be used to compare data such as: SELECT INTERVAL(6,1,2,3,4,7,8,9,10) will return 4, because When comparing, mysql will use the data with index 0 to compare the next data. When the next data is greater than the data with index 0, mysql will return the index of the previous data |
IS | IS keyword in mysql is only used in IS NULL or IS NOT NULL such as: SELECT * FROM USER where update_time IS NULL |
JOIN | is used to connect two tables. The connection methods are generally inner joinINNER JOIN and right joinRIGHT JOIN , left connectionLEFT JOIN |
KEY | KEY is the physical structure of the database, which has two levels of meaning and function: 1: Constraints, 2: Index, such as the declaration of the primary key PRIMARY KEY (id), , which will have unique constraints and automatically add the index |
KILL | is used to terminate the thread in mysql. You can use SHOW PROCESSLIST to view the current thread, and use KILL thread id to terminate the thread. There are two modifiers 1: CONNECTION default The modifier can terminate all connections related to the thread id. 2: QUERY terminates the currently executed statement, but will not terminate the connection |
LABEL | Statement label |
LEAVE | The Leave statement indicates exiting the flow control statement block of the specified label. It is usually used in begin...end, as well as loop, repeat, and while loop statements. Just like break in programming, the usage method is LEAVE loop name; |
LEFT | The LEFT() function is a string function that returns The left part of the string with the specified length.For example: SELECT LEFT(name,3) FROM user |
LIKE | is used for fuzzy search and can be used with % and _, % Represents querying one or more wildcard characters, and _ represents a character, such as: SELECT * FROM user WHERE name LIKE '%i' You can query all data ending with i in the name, replace % with _ After that, the query condition becomes querying the data whose name ends with i and has only one character in front |
LIMIT | is used for paging query, such as: SELECT * FROM user LIMIT 4,5 The first parameter is the starting number. As in the above example, it returns from the 4th piece of data. The second parameter is the offset. As shown in the above example, if the parameter is 5, it means returning. From the last five pieces of data in Article 4, the previous offset can be -1 to represent all the data after the starting number of queries. However, this writing method is officially recognized by MySQL as an error, so newer versions of MySQL cannot be used. , the best way is to give a relatively large number |
LOCALTIME | local time, which can be used as query result field, where condition, current time when inserting, update time, etc., mysql has a variety of time functions, you can choose different functions according to your needs, for example: SELECT LOCALTIME,NOW(),sysdate(), localtimestamp, localtimestamp(); |
LOCK | Locking tables and unlocking MySQL allows client sessions to explicitly acquire table locks to cooperate with other sessions to access the table, or to prevent other sessions from requiring mutually exclusive access when the session when modifying the table. A session can only acquire or release locks for itself. A session cannot acquire a lock from another session, nor can it release a lock held by another session. Example: LOCK table user read local At this time, a table lock operation will be generated. All operations to modify the table will be rejected and prompt: Table 'user' was locked with a READ lock and can 't be updated , you can use the unlock tables; keyword to unlock |
LOW_PRIORITY | low priority, MySQL allows you to change the statement Prioritization of scheduling, which allows queries from multiple clients to cooperate better so that a single client does not wait for a long time due to locks. Generally used in DELETE, INSERT, LOAD DATA, REPLACE and UPDATE statements, for example: update LOW_PRIORITY user set username = 'zhangsan' In this case, if the writer is waiting, the second When a reader arrives, the second reader is allowed to insert before the writer. Writers are allowed to start operations only when there are no other readers. |
MOD | Remainder function, such as: select mod(12,5) Return remainder 2 |
NATURAL | Natural join is a type of JOIN. It is characterized by automatically matching fields with the same name in the table. The types of these fields with the same name can be different, so the types of fields in the table can be different. , can be applied in INNER, LEFT and other JOINs, for example: select * from user NATURAL LEFT JOIN user2 The difference between user and user2 here is that in addition to the id, 1 will be added after the user2 field, which will result in The id is automatically used for association when connecting, and the result is indeed the same |
OPTIMIZE | Function: Optimize and organize table fragments and indexes, and the database will allocate data when storing data in the database Table space, and index to the data. When the data is deleted, the database will not reclaim these resources but wait for new data to fill these vacancies. Use the OPTIMIZE keyword to actively clear these occupied resources. Usage: optimize table table Name |
RANGE | Partition: Based on a given interval range, the value of this field in the given interval is required to be continuous when performing the operation Knowing how to partition accordingly can greatly improve efficiency. The requirement is that if the table has a primary key, the partition field should also be in the row 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 | Create Foreign key relationship, in the table creation statement: FOREIGN KEY(uid) REFERENCES users(id) means that the field uid will be connected to the primary key field id of the user table |
REGEXP | Regular expression, you can use regular expressions in conditions to operate, use SELECT * FROM user WHERE email NOT REGEXP'^[A-Z0-9._%-] @[A-Z0-9.-] .[A-Z]{2,4}$' |
RENAME | To modify the table name, use: rename table user2 to user3; |
REPEAT | Copy the given data as a string a specified number of times, such as: select REPEAT(3,3) The result is "333" |
REPLACE | Replace all specified strings, such as: select REPLACE('This is a string, or a character', 'one', 'two') ; |
REVOKE | Revoke the permissions that have been granted to the MySQL user, such as: revoke all on *.* from testUser@host; Remember to refresh the user permission table after completionFLUSH PRIVILEGES; |
RIGHT | Perform truncation operation on the string, such as:select RIGHT ('This is a string',5) , will intercept the specified number of digits in the string in reverse order |
RLIKE | Fuzzy query, different from like When , the content of rlike can be regular and may not match exactly, such as: select * from user where email RLIKE '^www.*$'; |
SEPARATOR | can concatenate the query results into one row with a string. SEPARATOR specifies the connector and needs to be used with GROUP BY, such as: SELECT *, GROUP_CONCAT(username order by username separator ';') SCORE FROM user GROUP BY email RLIKE '^www.*$' |
USING | If the field names are the same during connection query, they can be used as connection conditions, using It can appear instead of on, such as: select * from user left join students USING(quanxian) |
WHILE | Loop statement keywords, used in storage During the process, 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:=@sum-1; END WHILE; END CALL fun(); DROP PROCEDURE fun
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represents logical exclusive OR. When any operand is NULL, the return value is NULL. For non-NULL operands, if the two logical true and false values are different, the return result is 1. , otherwise 0, such as: | select true XOR null;select true XOR true;select true XOR false;
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When creating a table After adding this keyword to the numerical type, if there are not enough digits to insert, the corresponding digits will be automatically filled, 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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