Yes, MySQL allows the use of CASE expressions in the FROM clause to select specific rows. The syntax is: SELECT ... FROM table_name WHERE
AND CASE WHEN
THEN
; when
THEN
ELSE
END AS
, where
>
#MySQL FROM Can I use CASE expression later?
Answer:Yes
Detailed explanation:
MySQL allows use in the FROM clause CASE expression to select specific rows from a table. A CASE expression is essentially a conditional statement that can return different values based on given conditions.
Syntax:
SELECT ... FROM table_name WHERE AND CASE WHEN THEN WHEN THEN ELSE END AS
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Where:
-
is required before applying the CASE expression conditions met.
-
and
are the conditions to be evaluated.
-
is the value returned based on the condition.
-
is the default value returned if no condition is matched.
-
is the alias assigned to the result of the CASE expression.
Example:
Suppose there is a "customers" table with the following columns:
We can use CASE expression to select from a specific country/ Customers by Region:
SELECT * FROM customers WHERE country = 'United States' AND CASE WHEN age > 18 THEN 'Adult' WHEN age <= 18 THEN 'Minor' ELSE 'Unknown' END AS `age_group`;
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This query will return all customers from the United States and classify them as adults, minors, or unknown based on age.
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