英语update和modify区别？

Definition and Usage:

a) Update: The term "update" is used to describe the modification of data or fields within a database table. This involves altering the values stored in specific columns, including changing their types (integer, string, etc.) and/or modifying their lengths. b) Modify: The word "modify" typically refers to the action of adjusting or altering a file's attributes, rather than updating the content of a database table directly. In this context, modifications may involve changing the format or type of the data stored within the file, such as changing its size or converting it from one data type to another. 2. Declaration vs Execution:

a) Update: When updating a table using the update statement, you would typically use the following syntax:

UPDATE my_table
SET column1 = new_value1, column2 = new_value2, ... WHERE condition;

This command indicates that you want to modify the values stored in all specified columns within the my_table table based on a certain condition (e.g., by an equality comparison for column1, a NOT NULL constraint for column2, etc.).

b) Modify: To execute a modification in a file, you might use the following syntax:

echo "ALTER TABLE my_table MODIFY column1 VARCHAR(100);"

This command sets the value of a column in the my_table table to a string with a maximum length of 100 characters, effectively modifying its data type.

Commiting vs Executing:

a) Update: After executing an update statement, you must commit changes to persist them to the database system. To do so, you typically use the COMMIT command followed by the SQL keyword after the command:

COMMIT;

This ensures that the changes made during the update operation are successfully saved to the database, allowing other operations to proceed.

b) Modify: Once the modification is complete, it becomes immediately effective. If you don't explicitly commit the changes using COMMIT, they will remain in the original state until you make a subsequent attempt to update or modify the same table again. In summary, while both "update" and "modify" denote changes made to database records, they differ in scope, execution process, and the requirements for committing these changes. The choice between updating and modifying depends on the specific application's needs, including determining whether to make changes to a single record or the entire table at once, as well as considering how data is modified, committed, and persisted across multiple stages.