Here are a few suitable question-based titles for your article, focusing on the key difference and usage: * Case Expression vs. Case Statement in MySQL: Which is Right for Your Query? * MySQL\'s Case

Case Expression vs Case Statement

MySQL provides two constructs called Case Expression and Case Statement, which may appear interchangeable. However, understanding their specific functionalities is crucial.

Case Expression

The Case Expression evaluates conditions and returns a corresponding result. It is typically used within expressions, such as in a SELECT statement or as a part of another expression. The syntax is:

CASE 
  WHEN [condition] THEN result 
  [WHEN [condition] THEN result ...] 
  [ELSE result] 
END

For example:

SELECT CASE
    WHEN type = 1 THEN 'foo'
    WHEN type = 2 THEN 'bar'
    ELSE 'baz'
END AS name_for_numeric_type
FROM sometable`

Case Statement

Unlike the Case Expression, the Case Statement executes one of a set of statements based on a condition. It is typically used in stored programs to perform conditional operations. The syntax is:

CASE
  WHEN search_condition THEN statement_list
  [WHEN search_condition THEN statement_list] ...
  [ELSE statement_list]
END CASE

For example:

CASE
    WHEN action = 'update' THEN
        UPDATE sometable SET column = value WHERE condition;
    WHEN action = 'create' THEN
        INSERT INTO sometable (column) VALUES (value);
END CASE

Key Difference

The primary distinction between Case Expression and Case Statement lies in their evaluation output. The Case Expression returns a value, while the Case Statement executes a set of statements. This difference determines their appropriate use cases.

Syntactical Variations

While the Case Expression syntax is consistent across MySQL versions, the syntax for Case Statements can vary between stored programs and normal queries. When used in normal queries, the keyword "END" is omitted, while in stored programs, it is required.

**Stored Program**

CASE
WHEN ...
...
ELSE ...
END CASE

**Normal Query**

CASE
WHEN ...
...
ELSE ...
CASE

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