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- What does decimal mean in mysql?
- The DECIMAL data type in MySQL is used to store exact decimal numbers with a decimal point. Features include: Precision: specified by number of digits and fixed number of decimal places. Range: Allows storing large or small decimal values, depending on precision. Precision Guarantee: Unlike floating point types, DECIMAL is guaranteed to store the exact value, avoiding rounding errors. Syntax: DECIMAL(precision, scale), precision specifies the total number of digits, and scale specifies the number of decimal places. Usage scenarios: monetary calculations, measurement, science, finance and accounting, etc. where precise calculations are required.
- Mysql Tutorial 1104 2024-05-01 20:09:54
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- The command to delete a table in mysql is
- The command to delete a table in MySQL is DROP TABLE, and its syntax is: DROP TABLE table_name; this command will permanently delete the specified table and all data in it, so be careful before using it; if the table has foreign key constraints, you need to delete the foreign key constraints first. Delete the table; the DROP TABLE operation is irreversible. Please make sure you have backed up the data in the table before deleting.
- Mysql Tutorial 467 2024-05-01 20:09:31
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- How to write the youngest age in mysql
- To find the minimum age value in MySQL: SELECT MIN(age) FROM table_name; This query returns the minimum value of the age column calculated by the MIN() function.
- Mysql Tutorial 556 2024-05-01 20:09:13
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- What does default value in mysql mean?
- Default values in MySQL are predefined values automatically assigned by the database when an insert operation does not specify a column value. They are used to ensure data consistency, simplify data entry, and prevent invalid/null values. Default values can be set through the DEFAULT keyword when creating a table or column, and types such as constant values, expressions, and NULL are supported. MySQL also provides special default values such as NULL (for a null value), CURRENT_TIMESTAMP (for inserting a timestamp), CURRENT_DATE (for inserting a date), and CURRENT_USER (for inserting a user name).
- Mysql Tutorial 649 2024-05-01 20:06:56
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- How to modify field name in mysql
- You can modify the field name in MySQL through the following steps: Use the ALTER TABLE statement to modify the field name directly. After making the modification, update the application and query code that references the field name. When changing the primary key field name, the primary key needs to be re-created. Changing field types and names can also be performed simultaneously. Multiple fields can be renamed simultaneously by using multiple CHANGE clauses.
- Mysql Tutorial 1110 2024-05-01 20:06:34
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- Instructions to delete database in mysql
- The command to delete a database in MySQL is DROP DATABASE, and its syntax is: DROP DATABASE database_name;. This statement will permanently delete the database with the specified name and all data in it, and cannot be recovered. DROP permission is required to execute this statement, and ensure that there is no required data in the database.
- Mysql Tutorial 824 2024-05-01 20:06:12
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- Will or be indexed in mysql?
- In MySQL, whether an OR query uses an index depends on the following factors: index coverage, order of index selection, and index type. To optimize OR queries, you can take the following steps: 1. Use a covering index; 2. Optimize index selectivity; 3. Use query rewriting; 4. Use multiple queries with UNION.
- Mysql Tutorial 1062 2024-05-01 20:03:57
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- How to use unique in mysql
- UNIQUE constraints in MySQL ensure that the values of a specific column or column group are unique in the table. The specific usage is as follows: Use the ALTER TABLE statement to add UNIQUE constraints: ALTER TABLE table_name ADD UNIQUE (column_name); Specify UNIQUE constraints when creating the table: CREATE TABLE table_name (column_name UNIQUE);
- Mysql Tutorial 1106 2024-05-01 20:03:37
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- The difference between null and (null) in mysql
- In MySQL, NULL represents a null value and takes up no space, while (NULL) is an empty string value and takes up 1 byte of space. Their differences include: different storage methods, different comparison methods, different insertion methods, different aggregate function processing methods, and different index usage.
- Mysql Tutorial 1011 2024-05-01 20:03:14
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- What does null mean in mysql?
- NULL in MySQL is a special placeholder that represents an unknown or non-existent value. It is different from the empty string or 0, and is not equal to itself or any other value. To handle NULL, you can use the special operators IS NULL and IS NOT NULL. Additionally, functions such as COALESCE(), IFNULL(), and NVL() can help handle NULL values. Best practices include avoiding NULL, using default values, and using explicit operators to compare NULL values.
- Mysql Tutorial 1144 2024-05-01 20:00:47
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- The difference between null and (null in mysql
- The difference between NULL and (NULL) in MySQL is as follows: NULL represents an unknown value, while (NULL) represents an explicit null value. NULL occupies no storage space, while (NULL) occupies one byte. NULL is not equal to any value, while (NULL) is equal to itself. NULL is used to represent missing or inapplicable data, while (NULL) is used to explicitly set a field to null.
- Mysql Tutorial 1083 2024-05-01 20:00:24
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- How to store null in mysql
- A NULL value in MySQL represents unknown or non-existent and is stored as a 1-bit bit field flag located at the end of each column data value. This storage scheme efficiently represents NULL values with only 1 bit, allowing fast checking and reducing storage space.
- Mysql Tutorial 1042 2024-05-01 19:57:49
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- What type of data can be stored in blob fields in Oracle?
- Oracle BLOB fields can store the following data types: images, video, audio, documents, application packages, and database backups, as well as any other custom binary data created by the application.
- Oracle 624 2024-04-30 09:09:12
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- Usage of nvl in oracle
- The NVL function in Oracle is used to replace values with NULL. The syntax is NVL(value, default_value). Usage includes: checking and replacing NULL with default values; avoiding calculation and aggregation errors; ensuring database integrity.
- Oracle 403 2024-04-30 09:03:15
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- What data objects are there in oracle
- Oracle database data objects include: tables (storage data collections), views (virtual tables), sequences (automatically generate unique values), indexes (speed up retrieval), primary keys (uniquely identify rows), foreign keys (join table data), triggers implements (automatically execute code), stored procedures (encapsulate tasks), functions (return calculated values), and packages (reuse code collections).
- Oracle 445 2024-04-30 09:00:27
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