current location：Home > Technical Articles > Database > SQL
- 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：
-
- What are the two categories of data operations in relational databases?
- Data operations in relational databases are divided into two categories: query and update. Query statements are used for various retrieval operations, and update operations are used for operations such as insertion, deletion, and modification.
- SQL 12078 2020-08-29 11:32:28
-
- When creating a crosstab query, where does the value of the column header field appear in the crosstab?
- When you create a crosstab query, the value of the column header field appears in the crosstab at the first row. A crosstab query groups the fields from a table. One group of columns is on the left side of the data table as the row fields of the crosstab, and the other group of columns is on the top of the data table as the column fields of the crosstab.
- SQL 10375 2020-08-29 11:32:12
-
- What is the syntax structure of select statement in SQL?
- The syntax structure of the select statement in SQL is: "SELECT select_list [ INTO..] FROM table_name [ WHERE...] [ GROUP BY...][ HAVING...][ ORDER BY...];".
- SQL 11914 2020-08-29 11:30:46
-
- What are the commonly used methods for sql optimization?
- Commonly used methods for sql optimization include: 1. Try to avoid full table scans, and consider establishing indexes on the columns involved in where and order by; 2. Try to avoid making null value judgments on fields in the where clause; 3. Use with caution in and not in; 4. Try to avoid large transaction operations and improve system concurrency.
- SQL 8265 2020-08-24 13:12:38
-
- Why does invalid column index appear in sql
- Reasons for invalid column index in sql: 1. The placeholder is inconsistent with the number of parameters; 2. SQL splicing error, please note that each [%] must be included with [''], and spliced with the parameters with [||]; 3 , wrong annotation.
- SQL 6206 2020-08-22 10:07:06
-
- What is the difference between deleting table data and deleting table structure in SQL?
- The difference between deleting table data and deleting table structure in SQL: 1. Deleting table data, the table structure is still there, while deleting table structure means deleting the entire table, including structure and data; 2. Different commands, deleting table data [ delete from table name], and the delete table structure is [drop table table name].
- SQL 5859 2020-08-19 14:42:32
-
- What are the characteristics of a trigger?
- Characteristics of triggers: 1. Automatic execution; triggers are activated immediately after any modifications are made to the data in the table. 2. Cascading updates; triggers can make cascading changes through related tables in the database. 3. Strengthen constraints. 4. Track changes. 5. Enforce business logic; triggers can be used to perform administrative tasks and enforce complex business rules that affect the database.
- SQL 13676 2020-08-18 11:49:34
-
- How to recover accidentally deleted database data
- How to recover accidentally deleted database data: first run Recovery for SQL Server and select the recovered data in recovery; then select Custom and select the [search..] option; then select the target folder and click Start; finally select the target database .
- SQL 18225 2020-08-12 09:55:15
-
- Briefly describe the basic principles of database design
- Basic principles of database design: 1. Store data with the same theme in a data table; 2. Try to eliminate redundancy and improve the speed of database access; 3. When designing the data table structure, the dynamic adaptation of the table structure should be considered sex.
- SQL 4122 2020-08-11 10:47:16
-
- Does sql between include both ends?
- In SQL, the BETWEEN operator is used to select values within the data range between two values. Among them, "between and" includes boundary values, that is, including both ends; "not between" does not include boundary values.
- SQL 23869 2020-07-28 15:39:04
-
- How to set primary key in sql database?
- Setting method: 1. Use the SQL Server Management Studio tool to connect to the database; 2. Expand "Table" in the database, right-click the data table that needs to be set, and select "Design"; 3. In the table designer interface, right-click the corresponding OK, select "Set Primary Key" to complete the setting of the primary key, click Save.
- SQL 41357 2020-07-28 10:54:29
-
- What is SQL's advanced and oriented operating language?
- SQL is a highly non-procedural and set-oriented operating language. When using SQL to perform data operations, users only need to ask "what to do" instead of specifying "how to do it". Therefore, users do not need to know the access path. The selection of the access path and the operation process of the SQL statement are automatically completed by the system; SQL uses sets Operation method.
- SQL 9063 2020-07-24 15:50:44
-
- How to differentiate between left outer join, right outer join and full outer join?
- A left outer join will return all records in the left table that are equal to the join fields in the right table; null if there is no data in the right table. A right outer join will return all records in the right table that are equal to the join fields in the left table; null if there is no data in the left table. A full outer join will return all records in the left and right tables that are equal to the join fields in the left and right tables.
- SQL 13974 2020-07-21 15:05:04
-
- How to create a view in sql database?
- How to create a view in sql database: 1. Log in to "sql server managment"; 2. Select "View" in the specified database, right-click and select the "New View" option; 3. Add the table to be associated; 4. The default is the primary key If it is related, you can adjust the related fields; 5. Press "ctrl+s" to save.
- SQL 24605 2020-07-20 14:40:42
-
- What is the extension of access?
- The access file extension before the 2007 version is [mdb]; the access file extension after the 2007 version is [accdb]. [Microsoft Office Access] is a database management system that Microsoft combines the graphical user interface of the database engine and software development tools.
- SQL 17370 2020-07-18 11:02:10
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
