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Definition and Usage. The CASE statement goes through conditions and return a value when the first condition is met (like an IF-THEN-ELSE statement). So, once a condition is true, it will stop reading and return the result. If no conditions are true, it will return the value in the ELSE clause.
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MySQL CASE expression is a control flow structure that allows you to add if-else logic to a query. Generally speaking, you can use the CASE expression anywhere that allows a valid expression e.g., SELECT, WHERE and ORDER BY clauses. The CASE expression has two forms: simple CASE and searched CASE.
For the first syntax, case_value is an expression. This value is compared to the when_value expression in each WHEN clause until one of them is equal. When an equal when_value is found, the corresponding THEN clause statement_list executes.
Use a simple CASE statement to evaluate a specific expression against a series of possible values and execute corresponding actions. Use a searched CASE statement to evaluate various conditions individually, allowing for a more flexible code.
CASE in MySQL is both a statement and an expression, where each usage is slightly different. As a statement, CASE works much like a switch statement and is useful in stored procedures, as shown in this example from the documentation (linked above):
CASE WHEN condition THEN result [WHEN condition THEN result...] [ELSE result] END. The first CASE syntax returns the result for the first value=compare_value comparison that is true. The second syntax returns the result for the first condition that is true.
26 sty 2024 · The CASE-WHEN statement in MySQL 8 is a robust tool for building dynamic and responsive SQL queries. Varying from basic conditional output to more complex evaluations involving subqueries and joins, CASE-WHEN can help you derive nuanced insights from your data in an elegant fashion.
