MySQL: Handling NonEmpty IF Conditions（mysqlif不为空）
Today, I’m going to discuss a common programming task when working with MySQL: handling non-empty IF conditions.
When interacting with a MySQL database there are many situations where a conditional statement is used to determine the action to take. Often times this comes in the form of an IF statement, which can either be true or false. The code for an IF statement looks something like this:
“`SQL
IF
THEN
END IF;
The condition portion is evaluated to check whether it is true or false, and the action portion is executed if the condition is true. However, if we want to allow for cases when the condition may be empty (or null) then this can present a problem. In this case, the IF statement will always evaluate to true, and our action will always execute.
To handle this situation we can use a variation of the IF statement – the IF ELSE statement. This statement evaluates the condition, and then takes one of two possible actions depending on the result. The code for the IF ELSE statement looks something like this:
```SQL IF
THEN
ELSE
END IF;
In this case, if the condition evaluates to true, action1 will be executed. Otherwise, if the condition is false, or if it’s empty, action2 will be executed. This allows us to handle both cases without the action being executed regardless of the condition.
Finally, if we want to make sure that the action is only executed if the condition is something other than empty, we can use the IF IS NOT NULL statement. This statement checks if the condition contains a value, and then executes action1 only if it does. The code for this statement looks something like this:
“`SQL
IF IS NOT NULL
THEN
END IF;
This statement checks whether the condition contains a value, and if it does it executes action1. If the condition is empty, on the other hand, the statement will never be evaluated and action1 will not be executed.
In conclusion, handling non-empty IF conditions in MySQL can be a tricky task, but with the use of IF ELSE and IF IS NOT NULL statements we can easily make sure our desired action is only executed when the condition is valid.
