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：
-
- 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 1223 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 1096 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 902 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 979 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 816 2024-05-02 04:48:18
-
- What does != mean in sql?
- In SQL queries, the != operator means "not equal to" and compares two expressions. If the results are different, it is true, if the results are the same, it is false. Syntax: expression1 != expression2. For example: SELECT * FROM customers WHERE age != 30; This query returns all customer records whose age is not equal to 30.
- SQL 1241 2024-05-02 04:42:15
-
- How to express inclusion in sql
- The IN operator is used in SQL to express inclusion, and its syntax is "column_name IN (value1, value2, ...)". Extended representations include NOT IN, ANY, and ALL, which check whether a value is not in a list, exists in a subquery, or exists in all subquery rows.
- SQL 436 2024-05-02 04:39:16
-
- What does mod in sql mean?
- MOD in SQL is the operator that calculates the remainder. Usage: MOD(x, y), where x is the dividend and y is the divisor. Returns the remainder after dividing x by y, which is always a nonnegative number. Use cases include calculating the day of the week, checking parity, and detecting whether a number is a multiple.
- SQL 583 2024-05-02 04:36:14
-
- What does union mean in sql?
- UNION is an operator in SQL that combines the result sets of two or more SELECT statements and returns a new result set that contains all unique rows. UNION only applies to SELECT statements with the same structure (consistent number of columns and data types) and automatically eliminates duplicate rows.
- SQL 480 2024-05-02 04:27:15
-
- How to use replace function in sql
- The REPLACE function in SQL is used to replace all given substrings with another substring in a text or string. Can be used for basic replacement, conditional replacement, and NULL value handling. The basic syntax is: REPLACE(string, old_substring, new_substring).
- SQL 811 2024-05-02 04:21:16
-
- How to use union in sql
- The UNION operation combines rows from different tables into a single result set, removing duplicate rows. The syntax format is: SELECT column_list FROM table1 UNION SELECT column_list FROM table2..., where table1 and table2 are the tables to be merged. The UNION operation requires that the participating tables have the same number of columns and data types, and that duplicate rows are removed.
- SQL 969 2024-05-02 04:18:17
-
- Usage of char in sql
- The char data type in SQL is a string type used to store fixed-length character data. Each character occupies one byte and is suitable for data that requires a specified length. Its advantages include fixed storage space, convenient comparison and sorting, and improved querying. Performance, but the disadvantage is low storage space utilization and the need to deal with Unicode character set compatibility issues. Unlike varchar, char has a fixed storage space, while varchar allows variable character length and dynamically allocates storage space.
- SQL 1258 2024-05-02 04:15:26
-
- The meaning of having in sql
- The HAVING clause is used to filter grouped data in a SQL query. Unlike the WHERE clause, which filters individual rows, the HAVING clause is used to filter groups created by the GROUP BY clause. Uses include: filtering summary values based on groups, applying aggregate function conditions, and filtering groups that meet specific conditions.
- SQL 680 2024-05-02 04:12:17
-
- What does having mean in sql
- The HAVING clause is used to filter aggregate results in SQL queries and filter rows that meet specific conditions. The HAVING clause can only be used with a GROUP BY clause, and conditions can reference aggregate functions and grouping columns.
- SQL 566 2024-05-02 04:09:14
-
- How to use having in sql
- The HAVING clause is used to filter grouped data. The syntax is: SELECT aggregate_functions(column_name) FROM table_name GROUP BY column_name HAVING condition;. It can filter on aggregate functions, grouping columns, constants or operators. For example, the following query filters out groups with at least 3 items in the order and a total amount greater than $100: SELECT COUNT(DISTINCT order_id) AS order_count FROM orders GROUP BY cus
- SQL 1149 2024-05-02 04:06:17
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
