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Conditional Operators

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    Case expressions evaluate conditional logic in an expression.

    case-expr:

    simple-case-expression | searched-case-expression

    Simple case expressions

    simple-case-expr:

    CASE expression  ( WHEN expression THEN expression)
         [ ( WHEN expression THEN expression) ]*
         [  ELSE expression ]  END

    Simple case expressions allow for conditional matching within an expression. The evaluation process is as follows:

    • The first WHEN expression is evaluated. If it is equal to the search expression, the result of this expression is the THEN expression.

    • If it is not equal, subsequent WHEN clauses are evaluated in the same manner.

    • If none of the WHEN expressions are equal to the search expression, then the result of the CASE expression is the ELSE expression.

    • If no ELSE expression was provided, the result is NULL.

    Searched case expressions

    searched-case-expression:

    CASE  ( WHEN  condition THEN expression)
           [( WHEN  condition THEN expression ) ]*
           [ ELSE  expression ] END

    Searched case expressions allow for conditional logic within an expression. The evaluation process is as follows:

    • The first WHEN expression is evaluated.

    • If TRUE, the result of this expression is the THEN expression.

    • If not TRUE, subsequent WHEN clauses are evaluated in the same manner.

    • If none of the WHEN clauses evaluate to TRUE, then the result of the expression is the ELSE expression.

    • If no ELSE expression was provided, the result is NULL.

    The following example uses a CASE clause to handle documents that do not have a ship date. This scans all orders. If an order has a shipped-on date, it is provided in the result set. If an order does not have a shipped-on date, default text appears.

    Query:
    SELECT
       CASE WHEN `shipped-on`
       IS NOT NULL THEN `shipped-on`
       ELSE "not-shipped-yet"
       END
       AS shipped
       FROM orders
    Result:
    { "shipped": "2013/01/02" },
    { "shipped": "2013/01/12" },
    { "shipped": "not-shipped-yet" },