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- How to write the default value in mysql
- How to set default values for columns in MySQL: specify the NOT NULL DEFAULT clause when creating a table, such as: CREATE TABLE users (name VARCHAR(255) NOT NULL DEFAULT 'John Doe'); use the ALTER TABLE statement to modify an existing table: ALTER TABLE table_name ALTER COLUMN column_name SET DEFAULT default_value, such as: ALTER TABLE users ALTER COLUMN name S
- Mysql Tutorial 539 2024-04-26 06:18:15
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- How to set the number of decimal places to 1 in mysql
- In MySQL, the methods to set the number of decimal places to 1 are: 1. Use the DECIMAL data type, the syntax is DECIMAL(precision, scale), where scale specifies the number of decimal places. 2. Use the CAST() function, with the syntax CAST(number AS DECIMAL(precision, scale)), to convert a decimal to a value with a specified number of decimal places.
- Mysql Tutorial 834 2024-04-26 06:15:22
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- Statement to delete database in mysql
- To delete a MySQL database, use the DROP DATABASE database_name; statement, where database_name is the name of the database to be deleted. Note: Back up data. Only users with DROP permissions can delete the database. Delete all objects in the database before deletion.
- Mysql Tutorial 786 2024-04-26 06:12:12
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- Command to delete database in mysql
- The command to delete a database in MySQL is DROP DATABASE, and the syntax is: DROP DATABASE database_name; Its usage is: connect to the server, specify database_name and run this command to delete the database.
- Mysql Tutorial 746 2024-04-26 06:09:12
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- Usage of all any in mysql
- ALL and ANY operators in MySQL are used to compare whether a collection meets a specific condition. ALL checks whether all elements are satisfied, while ANY only requires one element to be satisfied.
- Mysql Tutorial 400 2024-04-26 06:06:13
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- The difference between union and union all in mysql
- Difference between UNION and UNION ALL set operators in MySQL: UNION returns unique rows, while UNION ALL returns all rows, including duplicate rows. UNION sorts the result set in ascending order, while UNION ALL does not sort. Select UNION to eliminate duplicate rows, and UNION ALL to retain duplicate rows.
- Mysql Tutorial 654 2024-04-26 06:03:17
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- Usage of any in mysql
- The ANY operator in MySQL is used to check whether the evaluation result of a subquery expression returns TRUE for any row in the query result. Specifically, the ANY operator is used to: Check whether there are rows that meet the condition in the query results. Determines whether the set of all rows in the query results satisfies a specific condition.
- Mysql Tutorial 837 2024-04-26 06:00:29
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- What does union mean in mysql?
- UNION in MySQL is a union operator that is used to combine multiple result sets from different tables or queries into a new result set without duplicate rows. The columns in the new result set must have the same data type and order, but UNION does not support aggregate functions and ORDER BY clauses.
- Mysql Tutorial 594 2024-04-26 05:54:13
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- Usage of in in mysql
- The IN operator is used to check whether a value is contained in a list of values. The syntax is: SELECT * FROM table_name WHERE column_name IN (value1, value2, ..., valueN); The IN operator can be used with value lists, variables or subqueries, and supports multiple value type comparisons. It is more efficient than the OR operator, especially when the list contains multiple values.
- Mysql Tutorial 835 2024-04-26 05:51:14
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- What does @ mean in mysql
- The @ symbol in MySQL has two uses: specifying variables (@variable name) and connecting table or column names (@table name or @column name), indicating an alias of a temporary or derived table in the database.
- Mysql Tutorial 588 2024-04-26 05:48:12
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- The role of unique in mysql
- The UNIQUE keyword in MySQL creates a unique index, forcing the values of a specific column or column group in the table to be unique, preventing duplication, improving query speed, avoiding inserting duplicate data, and optimizing data storage.
- Mysql Tutorial 1129 2024-04-26 05:45:24
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- The role of primary key in mysql
- The primary key in MySQL is a column or combination of columns that uniquely identifies each row in a table. The main functions include: 1. Unique constraints: ensure that each row has a unique value; 2. Optimize query performance: serve as an index to improve query and sorting speed; 3. Foreign key reference: establish relationships between tables; 4. Auto-increment: insert Automatically generate unique consecutive integers when creating new rows; 5. Table constraints: limit data integrity and prevent duplicate values.
- Mysql Tutorial 851 2024-04-26 05:42:15
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- The role of in in mysql
- The IN operator in MySQL is used to check whether a column's value is in a specified list of values, allowing you to easily find records containing a specific value. The syntax is: SELECT column_name FROM table_name WHERE column_name IN (value1, value2, ..., valueN). When using the IN operator, MySQL checks the column values one by one to see if they match any value in the list, and if so, the record is included in the result set.
- Mysql Tutorial 563 2024-04-26 05:39:13
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- What does in in mysql mean?
- The IN operator in MySQL is used to check whether a value is contained in a specified list. The syntax is: SELECT column_name FROM table_name WHERE column_name IN (value1, value2, ..., valueN). Its advantages include high efficiency, ease of use, and scalability. Be aware that it may cause performance issues with large lists or NULL values.
- Mysql Tutorial 1174 2024-04-26 05:33:14
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- How to write not equal in mysql
- Expression of not equal to query condition in MySQL: use != operator to express not equal. For example: SELECT * FROM table_name WHERE column_name != value;
- Mysql Tutorial 476 2024-04-26 05:30:18
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