MySQL interview written test question set sharing

01. MySQL technical features?

Mysql database software is a client or server system that supports various Multi-threaded SQL server for client programs and libraries, different backends, extensive application programming interfaces and management tools

02, MySQL default port number?

3306

03. What are the advantages of MySQL?

MySQL is open source software and can be used at any time without paying. Provides management tools for managing, checking, and optimizing database operations, a GUI with a command prompt, supports multiple storage engines, and supports multi-threading to fully utilize CPU resources

04, MySQL supported Storage engine and features?

MySQL5.7 supports: InnoDB, MyISAM, MERGE, MEMORY, ARCHIVE, CSV, PERFORMANCE_SCHEMA, BLACKHOLE

InnoDB is the current default transaction of MySQL The storage engine is currently the most important and widely used storage engine. It supports transaction-safe tables, row locking and foreign keys.

MyISAM is based on the ISAM storage engine and extends it. MyISAM has a higher insertion efficiency , query speed, but does not support things and foreign keys

MERGE storage engine is a combination of a set of MyISAM tables. The MyISAM table structure must be exactly the same

MEMORY storage engine stores the data in the table to In memory, data from other tables is not queried or referenced to provide quick access

PERFORMANCE_SCHEMA engine is mainly used to collect database server performance parameters

05. How to check the MySQL version ?

SELECT VERSION();

06. The difference between char and varchar?

The CHAR column length is fixed to the length declared when creating the table, and the length value range is 1 to 255. When CHAR values ​​are stored, they are padded with spaces to a specific length. Trailing spaces need to be removed when retrieving CHAR values.

The VARCHAR column length can be changed to the length declared when creating the table. When the VARCHAR value is stored, the length is automatically changed (can be made smaller)

07, fuzzy query like What do % and _ mean?

% means 0 or more characters, _ means 1 character.

08. Is MySQL query case-sensitive?

MySQL is not case-sensitive

09. How to query in MySQL 50 records?

SELECT * FROM 表名 LIMIT 0,50;

10. What are the differences between NOW() and CURRENT_DATE()?

NOW() command is used to display the current year\month \Day\Hour\Minute\Second

CURRENT_DATE() only displays the current year\month\day

11. What is InnoDB?

InnoDB It is one of the database engines of MySQL and is now the default storage engine of MySQL. InnoDB was developed by Innobase Oy and supports ACID-compatible transaction functions

12. When the column is set to AUTO INCREMENT, if What happens when the maximum value is reached in the table?

Stop incrementing, any further insertion will generate an error

13. How do you view all indexes defined in the table?

SHOW INDEX FROM 表名\G;

14. A table has a column defined as TIMESTAMP, what will happen

Whenever a row is changed, the timestamp field will get the current timestamp.

15. How to distinguish between FLOAT and DOUBLE?

Floating point numbers are stored in FLOAT with 8-bit precision and have four bytes; floating-point numbers are stored in DOUBLE with 18-bit precision and have eight bytes

16. How many TRIGGERS are allowed in a MySQL table?

17. What is the difference between LIKE and REGEXP operations?

LIKE matches the entire column. If the matched text appears in the column value, LIKE will not find it and the corresponding row will not be returned (no wildcards are used)

REGEXP matches within a column value. If the matched text appears within the column value, REGEXP will find it and the corresponding row will be returned.

18. What is the difference between CHAR_LENGTH and LENGTH functions?

CHAR_LENGTH is the number of characters, and LENGTH is the number of bytes. The two data of Latin characters are the same. But they are different for Unicode and other encodings

19. What is the statement to import/export database data?

Import-->mysql -u username-p password database name

Export-->mysqldump -u username-p database name> Exported file name

20. There is an ID auto-incrementing primary key in a table. After inserting 17 records, delete the 15th, 16th, and 17th records. Restart MySQL and insert again. A record, is the ID of this record 18 or 15?

If the type of table is InnoDB, it is 15;

If the type of table is MyISAM, then It's 18.

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