What are the characteristics of ‘when’ in MySQL?

In MySQL, “when” is a conditional statement used to perform different operations based on the condition when executing SQL statements. Here are some characteristics of “when”:

1. “when” is typically used in combination with a “case” statement to execute different blocks of code based on different conditions.
2. “when” can be used with multiple conditions, each condition can have one or more branches, corresponding to different actions.
3. You can use “when” to make conditional judgments, such as determining if a certain field meets the requirements.
4. The “when” statement checks each condition from top to bottom, and once a condition is met, it executes the corresponding operation and skips the rest of the conditions.
5. The “when” statement can be used for data transformation or calculation, such as mapping field values to other values or performing mathematical operations.
6. The “when” statement can be nested, allowing for more complex conditional judgments within a branch.
7. In the “when” statement, comparison operators (such as equal to, greater than, less than, etc.) can be used for condition testing.
8. The “when” statement can be used in conjunction with other SQL statements (such as SELECT, UPDATE, DELETE, etc.) to perform corresponding operations based on conditions.

In conclusion, the “when” statement in MySQL is a very useful conditional statement that allows for executing different operations based on different conditions, thereby achieving flexible data processing and transformation.