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 syntax is used to decrement fields in sql
- Using the AUTO_INCREMENT keyword in SQL can realize field decrement, that is, when inserting a new record, the integer field specified as decrement will automatically increment. Notes include: Decrementing fields must be unique primary keys or unique indexes, cannot be used with DEFAULT or NOT NULL constraints, and can only be used in INSERT operations.
- SQL 1149 2024-05-07 04:42:14
-
- What command is used to create a basic table in sql
- The command to create a basic table in SQL is CREATE TABLE. It is used to create a basic table with column names, data types and constraints like NOT NULL, DEFAULT.
- SQL 990 2024-05-07 04:39:14
-
- How to use date functions in sql
- Date functions are functions used to manipulate dates and times in SQL queries. Common date functions include getting the current date (CURDATE()), formatting the date (DATE_FORMAT()), adding or subtracting time intervals from the date (DATE_ADD(), DATE_SUB()), and extracting the time part (EXTRACT()) and converting strings to date values (STR_TO_DATE()). These functions are commonly used to process date-related data, such as getting the current date, formatting dates to meet specific needs, calculating the difference between dates, etc.
- SQL 588 2024-05-07 04:36:17
-
- Can an insert statement have a where condition?
- The insert statement does not allow the use of where conditions because where conditions are used to select rows for operation. Alternatives include: 1. Trigger: checks the condition and performs the action when a new row is inserted; 2. Stored procedure: performs the condition check before inserting the new row and performs the action based on the result; 3. Application logic: executes in the application The condition is checked and decided whether to insert a new row or not.
- SQL 791 2024-05-06 15:51:12
-
- How to use insert statement
- The INSERT statement can insert new rows into the database table. The syntax is: INSERT INTO table_name (column1, column2, ..., columnN) VALUES (value1, value2, ..., valueN); The steps are as follows: 1. Specify the table name; 2. List the column names into which values are to be inserted; 3. List the corresponding values; 4. End the statement with a semicolon.
- SQL 1251 2024-05-06 15:48:17
-
- Usage of insert statement in SQL
- The INSERT statement is used to insert new records into a database table. The syntax is: INSERT INTO table name (column 1, column 2, ...) VALUES (value 1, value 2, ...); the INSERT statement has the following variants: select data insertion from other tables or subqueries, If the primary key conflicts, the existing record will be updated. If the primary key conflicts, the insertion will be ignored. When no column name is specified, values are inserted in the order defined by the table; no value is required for auto-increment columns; the number of affected rows is 1 on successful insertion; an error is thrown on failure.
- SQL 1209 2024-05-06 15:45:25
-
- Is there a difference between null and 0 in sql?
- NULL and 0 are different values in SQL: NULL represents an unknown or non-existent value, and 0 represents the numeric value zero. NULL cannot be compared with any value and returns NULL when participating in arithmetic operations; 0 can be compared and participated in arithmetic operations. NULL returns NULL when participating in logical operations, and 0 is considered false. NULL and numeric values are handled differently in database operations, such as in conditional checks.
- SQL 1456 2024-05-02 05:27:19
-
- The difference between null and empty in sql
- In SQL, NULL represents an unknown or non-existent value. It has its own data type and cannot be indexed. It usually takes up less storage space and is FALSE in Boolean expressions. Null represents an empty string, which has a string data type and can be indexed, considered TRUE. Use NULL to indicate that the data is unknown, and use NULL to indicate that the data is an empty string.
- SQL 1055 2024-05-02 05:24:17
-
- What does a null value represent in mysql?
- Null values in MySQL are represented as NULL, indicating that the data does not exist or is unknown. The advantages of using NULL include accuracy, consistency, data integrity, and query optimization, but the disadvantages include potential ambiguity, additional processing, and storage overhead. Other ways to represent null values include the empty string, the number 0, and special characters, but there are data type conversion and ambiguity issues with using these methods.
- SQL 1013 2024-05-02 05:21:16
-
- What does sage mean in sql
- SAGE (SQL Anywhere Generalized Extraction) in SQL Anywhere is a feature used to extract and transform data from relational databases for purposes including data extraction, integration, transformation, and reporting.
- SQL 717 2024-05-02 05:12:15
-
- Usage of decimal in sql
- The DECIMAL data type in SQL is used to store exact decimal numbers. It has the following syntax: DECIMAL(precision, scale), where precision is the total number of digits and scale is the number of digits after the decimal point. DECIMAL is used to store financial data, monetary values, and other numbers that require high precision. Unlike FLOAT and DOUBLE, DECIMAL stores exact values without using scientific notation. It takes up more storage space than FLOAT or DOUBLE. You should use = and <> operators when comparing. If you need greater precision and range, you can use NUMER
- SQL 1396 2024-05-02 05:06:37
-
- Usage of decode in sql
- The DECODE function is used to evaluate different values based on a conditional expression, similar to the IF-ELSE syntax. Its usage includes: replacing NULL values, converting data types, and returning different values based on conditions.
- SQL 1255 2024-05-02 05:00:31
-
- begin end usage in sql
- In SQL, BEGIN and END are used as transaction boundary markers to ensure the atomicity, durability, and isolation of operations. BEGIN starts a transaction and END commits or rolls back the transaction. 1. BEGIN starts the transaction. 2. Perform an operation (insert, update, etc.). 3. COMMIT commits the transaction and makes the changes permanent. 4. ROLLBACK rolls back the transaction and undoes the changes.
- SQL 1009 2024-05-02 04:57:17
-
- The main function of rollback statement in sql
- The ROLLBACK statement can undo all changes in the current transaction and restore it to the state at the beginning of the transaction. Specific operations include: canceling uncommitted data operations, restoring the original values of modified records, and releasing transaction-locked resources. Use ROLLBACK when an error occurs in a transaction, the user wants to undo changes, or the database needs to be rolled back. It should be noted that ROLLBACK cannot undo DDL operations and can only affect the current transaction. Uncommitted changes will be lost after execution.
- SQL 1056 2024-05-02 04:54:15
-
- Usage of avg function in sql
- The AVG function in SQL is used to calculate the average of numeric values. Its syntax is AVG(column_name). AVG functions ignore NULL values. You can use the AS keyword to specify aliases for results. It only works for numeric type data, returning NULL if the target column has no value or contains only NULL values, and throwing an error if it contains non-numeric values.
- SQL 931 2024-05-02 04:48:18
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
