What do when and case mean in sql?

WHEN and CASE in SQL are keywords used to check conditions and return specified values. WHEN is used to specify a condition. If the condition is true, the subsequent statement is executed; CASE is a control flow statement, which executes different statements according to the conditions that are met. The syntax is: CASE WHEN THEN WHEN ... ELSE END. The condition can be any valid SQL expression, example: SELECT CAS

WHEN and CASE

in SQL What are WHEN and CASE?

WHEN and CASE are a set of keywords in SQL that are used to perform conditional checks and return specified values.

WHEN

• WHEN is a conditional keyword used to specify a condition in a CASE statement.
• If the condition is true, the subsequent statements are executed.

CASE

• CASE is a control flow statement used to execute different statements based on satisfied conditions.
• The CASE statement consists of one or more WHEN clauses and an optional ELSE clause.

How to use WHEN and CASE

The general syntax of the CASE statement is as follows:

CASE
  WHEN <condition1> THEN <result1>
  WHEN <condition2> THEN <result2>
  ...
  ELSE <default_result>
END

The condition can be any valid SQL expression, Such as comparisons, logical operations or subqueries.

Example

The following example uses the CASE statement to return customer status:

SELECT
  CASE
    WHEN status = 'A' THEN 'Active'
    WHEN status = 'I' THEN 'Inactive'
    ELSE 'Unknown'
  END AS customer_status
FROM customers;

Other tips

• You can use multiple WHEN clauses to handle multiple conditions.
• The ELSE clause is optional and is used to handle situations where no other conditions are met.
• The result of the CASE statement can be any data type.
• WHEN and CASE can be used to handle complex conditions and generate results dynamically.

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