如何在mySQL查詢中使用if（）函數？

答案是MySQL的IF()函數用於在查詢中執行簡單的條件判斷，語法為IF(condition, value_if_true, value_if_false)；它根據條件返回不同值，適用於SELECT、UPDATE等語句中的數據控制與轉換。

The IF() function in MySQL is a conditional function that allows you to perform simple if-else logic directly within a query. It evaluates a condition and returns one value if the condition is true, and another if it's false. This is useful for controlling output based on data values without needing application-level logic.

Syntax of IF() Function

The syntax for the IF() function is:

Where:

• condition : A logical expression that evaluates to TRUE or FALSE.
• value_if_true : The value returned if the condition is TRUE.
• value_if_false : The value returned if the condition is FALSE or NULL.

Basic Example: Conditional Output

Suppose you have a table called students with columns name and score . You want to display "Pass" if the score is 50 or above, and "Fail" otherwise:

This adds a calculated column result showing pass/fail status based on each student's score.

Using IF() in Calculations or Data Transformation

You can use IF() to modify values during queries. For example, in an orders table, you might apply a discount only to certain customers:

This gives a 10% discount (multiplies by 0.9) only to VIP customers.

Nesting IF() Functions for Multiple Conditions

While MySQL also supports CASE , you can nest IF() functions for multiple conditions. For instance, grading based on score ranges:

This checks each condition in order and assigns the appropriate letter grade.

Basically, the IF() function is a compact way to add conditional logic in MySQL SELECT, UPDATE, or even WHERE clauses. It's best for simple binary decisions. For more complex scenarios, consider using CASE for better readability.

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