current location：Home > Technical Articles > Daily Programming > Mysql Knowledge
- Direction：
- All web3.0 Backend Development Web Front-end Database Operation and Maintenance Development Tools PHP Framework Daily Programming WeChat Applet Common Problem Other Tech CMS Tutorial Java System Tutorial Computer Tutorials Hardware Tutorial Mobile Tutorial Software Tutorial Mobile Game Tutorial
- Classify：
- PHP tutorial MySQL Tutorial HTML Tutorial CSS Tutorial
-
- How to use avg in mysql
- MySQL's AVG() function is used to calculate the average of numeric values. It supports multiple usages, including: Calculate the average quantity of all sold products: SELECT AVG(quantity_sold) FROM sales; Calculate the average price: AVG(price); Calculate the average sales volume: AVG(quantity_sold * price). The AVG() function ignores NULL values, use IFNULL() to calculate the average of non-null values.
- Mysql Tutorial . Database 988 2024-05-01 21:16:09
-
- Statement to delete data table in mysql
- In MySQL, the statement to delete a data table is: DROP TABLE table name. This statement will permanently delete the data table with the specified name and all data in it, so you should ensure that the data is no longer needed before using it.
- Mysql Tutorial . Database 618 2024-05-01 21:15:48
-
- How to create an index in mysql
- A MySQL index is a data structure for finding data quickly, created by following these steps: Select columns that are frequently queried or sorted. Determine the normal, unique, compound, or full-text index type. Create the index using the CREATE INDEX statement (for example: CREATE INDEX idx_user_name ON users (name)). Optimize indexes, such as using covering indexes and deleting unused indexes.
- Mysql Tutorial . Database 633 2024-05-01 21:15:29
-
- How to modify fields in mysql
- To modify a field in MySQL, you need to perform the following steps: Use the ALTER TABLE statement, followed by the table name, field name and new data type, for example: ALTER TABLE my_table MODIFY age VARCHAR(255); Optional: add new fields, delete fields, rename fields Or modify the default value.
- Mysql Tutorial . Database 619 2024-05-01 21:12:38
-
- Are views in mysql useful?
- A MySQL view is a virtual table created based on a query, which provides the following advantages: Data abstraction and security: Hides the underlying table structure and provides a view of a subset of the data. Data integration: Connect multiple basic tables to form a unified virtual table. Improve query performance: Precompute query results to improve performance. Simplify application development: Provide a consistent view of data and reduce development burden. Permission control: restrict access to basic table data, implemented through view permissions.
- Mysql Tutorial . Database 601 2024-05-01 21:12:17
-
- The role of index in mysql
- Indexes play a role similar to book indexes in MySQL, optimizing query performance by enabling fast access to data and avoiding sequential table scans. Reduce I/O for sorting and grouping operations and increase query speed. Support unique constraints to prevent data duplication. Accelerate join queries to quickly match rows by primary key or unique index.
- Mysql Tutorial . Database 631 2024-05-01 21:09:56
-
- What is the instruction to delete database in mysql
- The command to delete a database in MySQL is DROP DATABASE, and its syntax is: DROP DATABASE database_name; When using it, please note that the database must be empty, and the deletion operation requires DROP permission.
- Mysql Tutorial . Database 795 2024-05-01 21:09:34
-
- What is the command to delete a user in mysql
- The command to delete a user in MySQL is DROP USER 'username', where 'username' is the username to be deleted. User permissions should be revoked before use. The deletion operation is permanent and cannot be undone.
- Mysql Tutorial . Database 408 2024-05-01 21:09:14
-
- What command is used to create a database in mysql
- The command to create a database in MySQL is CREATE DATABASE database_name;. You need to specify the name of the database to be created. For example, to create a database named "my_database", use CREATE DATABASE my_database;.
- Mysql Tutorial . Database 1087 2024-05-01 21:06:33
-
- What does value mean in mysql
- VALUE keyword in MySQL: 1. Get column value: SELECT value FROM table_name WHERE column_name = value; 2. Set column value: UPDATE table_name SET column_name = value WHERE condition.
- Mysql Tutorial . Database 753 2024-05-01 21:03:53
-
- Usage of decode function in mysql
- The DECODE function maps values based on a given condition: an expression is evaluated and matched against the condition value. If there is a match, the corresponding result value is returned; if there is no match, the default value is returned.
- Mysql Tutorial . Database 344 2024-05-01 21:03:32
-
- Does null take up space in mysql?
- Null takes up no space in MySQL. It only represents missing data, stored as the special value NULL, without taking up any actual storage space. Its storage mechanism uses bitmaps to set bits according to whether the field is Null, saving space, optimizing query performance, and avoiding data integrity issues. Note that the Null value is not equal to the empty string or the zero value, which takes up storage space.
- Mysql Tutorial . Database 364 2024-05-01 21:01:16
-
- The difference between null and empty values in mysql
- NULL represents an unknown and meaningless value, while null represents an unassigned or uninitialized value. The differences between the two are: semantic differences, database processing methods, query optimization impact, data integrity impact, which can be distinguished through the operators provided by MySQL.
- Mysql Tutorial . Database 532 2024-05-01 21:00:54
-
- Why does the COALESCE function in mysql fail?
- The reason why the COALESCE function in MySQL fails is that all the parameters are NULL. The parameter type is incompatible and the NULL expression is passed. A minor error.
- Mysql Tutorial . Database 455 2024-05-01 21:00:32
-
- What does from dual mean in mysql
- FROM DUAL is used in MySQL to retrieve data from the single-row virtual table DUAL. It is often used to get the current date and time, database version, or as a placeholder in a query or to execute a DDL statement.
- Mysql Tutorial . Database 763 2024-05-01 20:58:02
Recommended Articles
Tool Recommendations
jQuery enterprise message form contact code
jQuery enterprise message form contact code is a simple and practical enterprise message form and contact us introduction page code.
form button
2024-02-29
HTML5 MP3 music box playback effects
HTML5 MP3 music box playback special effect is an mp3 music player based on HTML5 css3 to create cute music box emoticons and click the switch button.
Player special effects
2024-02-29
HTML5 cool particle animation navigation menu special effects
HTML5 cool particle animation navigation menu special effect is a special effect that changes color when the navigation menu is hovered by the mouse.
Menu navigation
2024-02-29
jQuery visual form drag and drop editing code
jQuery visual form drag and drop editing code is a visual form based on jQuery and bootstrap framework.
form button
2024-02-29
Organic fruit and vegetable supplier web template Bootstrap5
An organic fruit and vegetable supplier web template-Bootstrap5
Bootstrap template
2023-02-03
Bootstrap3 multifunctional data information background management responsive web page template-Novus
Bootstrap3 multifunctional data information background management responsive web page template-Novus
backend template
2023-02-02
Real estate resource service platform web page template Bootstrap5
Real estate resource service platform web page template Bootstrap5
Bootstrap template
2023-02-02
Simple resume information web template Bootstrap4
Simple resume information web template Bootstrap4
Bootstrap template
2023-02-02
Cute summer elements vector material (EPS PNG)
This is a cute summer element vector material, including the sun, sun hat, coconut tree, bikini, airplane, watermelon, ice cream, ice cream, cold drink, swimming ring, flip-flops, pineapple, conch, shell, starfish, crab, Lemons, sunscreen, sunglasses, etc., the materials are provided in EPS and PNG formats, including JPG previews.
PNG material
2024-05-09
Four red 2023 graduation badges vector material (AI EPS PNG)
This is a red 2023 graduation badge vector material, four in total, available in AI, EPS and PNG formats, including JPG preview.
PNG material
2024-02-29
Singing bird and cart filled with flowers design spring banner vector material (AI EPS)
This is a spring banner vector material designed with singing birds and a cart full of flowers. It is available in AI and EPS formats, including JPG preview.
banner picture
2024-02-29
Golden graduation cap vector material (EPS PNG)
This is a golden graduation cap vector material, available in EPS and PNG formats, including JPG preview.
PNG material
2024-02-27
Home Decor Cleaning and Repair Service Company Website Template
Home Decoration Cleaning and Maintenance Service Company Website Template is a website template download suitable for promotional websites that provide home decoration, cleaning, maintenance and other service organizations. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-05-09
Fresh color personal resume guide page template
Fresh color matching personal job application resume guide page template is a personal job search resume work display guide page web template download suitable for fresh color matching style. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-02-29
Designer Creative Job Resume Web Template
Designer Creative Job Resume Web Template is a downloadable web template for personal job resume display suitable for various designer positions. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-02-28
Modern engineering construction company website template
The modern engineering and construction company website template is a downloadable website template suitable for promotion of the engineering and construction service industry. Tip: This template calls the Google font library, and the page may open slowly.
Front-end template
2024-02-28
