How to use ifelse sql statement

The IFELSE statement is a conditional statement that returns different values ​​based on the conditional evaluation result. Its syntax structure is: IF (condition) THEN return_value_if_condition_is_true ELSE return_value_if_condition_is_false END IF;.

Use of IFELSE statements in SQL

The IFELSE statement is a conditional statement that returns different values ​​based on the given condition evaluation result. Its syntax structure is as follows:

 <code>IF (condition) THEN return_value_if_condition_is_true ELSE return_value_if_condition_is_false END IF;</code>

How to use IFELSE statements

1. In the IF section, specify the conditions to be evaluated. The condition can be any boolean expression, for example:

   • column_name = 'value'
   • column_name IS NULL
   • value1 > value2

2. In the THEN section, specify the value to be returned if the condition is true. This can be any expression, for example:

   • 'true'
   • 1
   • column_name

3. In the ELSE section, specify the value to be returned if the condition is false. This can also be any expression, for example:

   • 'false'
   • 0
   • NULL

Example

The following query uses the IFELSE statement to determine the order status of a given customer:

 <code>SELECT customer_id, order_id, IF(order_status = 'Shipped', '已发货', '未发货') AS order_status FROM orders;</code>

This query returns a result set where the order_status column for each row shows the current status of the order, i.e. "Shipped" or "Unshipped".

Things to note

• IFELSE statements can be nested to handle more complex conditions.
• If the condition is NULL, a NULL value is returned.
• IFELSE statements are usually used alternately with CASE statements, which provides more flexible conditional processing.

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