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
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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
-
-
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
-
-
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
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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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