Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteA PL/SQL CASE expression returns a value; a CASE statement selects and runs one or more statements. Use an expression when a decision should produce a value, and a statement when each branch should take an action. Both can use a simple selector or searched conditions, but they differ in what each branch contains and what happens when nothing matches.
What is the difference between a CASE statement and a CASE expression in PL/SQL?
| Question | CASE expression | CASE statement |
|---|---|---|
| Purpose | Evaluates alternatives and returns a value. | Selects and executes the statements in one alternative. |
| Branch content | A result value for each THEN branch. |
One or more PL/SQL statements for each THEN branch. |
| Typical use | Assign a value or supply one within a larger expression. | Choose procedural actions, such as calling different procedures. |
| Closing syntax | Ends with END as part of the enclosing expression. |
Ends with END CASE;. |
No match and no ELSE |
Returns NULL. |
Raises the predefined CASE_NOT_FOUND exception. |
Oracle describes the expression in its PL/SQL expressions reference and the statement in its PL/SQL CASE statement reference. They are not interchangeable: an expression supplies a value, whereas a statement controls which procedural code runs.
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When should I use a CASE expression versus a CASE statement?
Choose an expression when the decision yields one value
Use a CASE expression to compute a label, category, or other result for an assignment or another expression. This illustrative assignment handles a null status explicitly:
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status_label := CASE
WHEN status_code IS NULL THEN 'Missing'
WHEN status_code = 'A' THEN 'Active'
ELSE 'Other'
END;The result of the expression is assigned to status_label. The expression itself does not call different procedures or perform a separate sequence of actions in each branch.
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Choose a statement when alternatives perform actions
Use a CASE statement when branches should execute different PL/SQL statements. This illustrative example dispatches on one status value:
CASE status_code
WHEN 'A' THEN activate_account;
WHEN 'S' THEN suspend_account;
ELSE log_unrecognized_status;
END CASE;The procedure names stand for procedures available in the surrounding PL/SQL program; declarations and any required arguments depend on that program. The statement chooses a branch and executes its statements rather than returning a result value.
How do simple and searched CASE forms work?
Both expressions and statements can be written as simple or searched CASE forms. In a simple form, one selector is compared with alternatives. In a searched form, each WHEN supplies a condition. These are illustrative syntax sketches, not complete grammar:
| Form | Expression | Statement |
|---|---|---|
| Simple | CASE selector WHEN value THEN result ... END |
CASE selector WHEN value THEN statement ... END CASE; |
| Searched | CASE WHEN condition THEN result ... END |
CASE WHEN condition THEN statement ... END CASE; |
Use simple CASE when alternatives compare one selector with specific values. Use searched CASE when branches need independent conditions, such as ranges or a test with IS NULL. If conditions overlap, put the intended highest-priority condition first.
Oracle documents ordered evaluation: alternatives are considered in order, and alternatives after a match are not evaluated. The selected branch is the first matching one. See Oracle’s CASE statement reference and expressions reference.
What happens if no WHEN clause matches in PL/SQL CASE?
The no-match outcome depends on whether the construct is an expression or a statement. With an ELSE, the expression returns the ELSE result and the statement executes the ELSE statements. Without an ELSE, their behavior differs:
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- Expression: evaluates to
NULL. - Statement: raises the predefined
CASE_NOT_FOUNDexception.
Oracle documents these outcomes in its PL/SQL CASE statement reference and PL/SQL expressions reference. Include an ELSE when a deliberate default is appropriate; otherwise, account for the expression’s possible null result or handle the statement’s exception.
Does CASE WHEN NULL match NULL in Oracle PL/SQL?
No. A simple CASE selector with a null value does not match WHEN NULL. Use a searched condition with IS NULL instead, for example:
CASE
WHEN status_code IS NULL THEN log_missing_status;
WHEN status_code = 'A' THEN activate_account;
ELSE log_unrecognized_status;
END CASE;For an expression, the same searched condition can return a value instead of executing a statement. Oracle’s PL/SQL control statements reference covers simple and searched case behavior.
Do SQL CASE expression rules also apply to PL/SQL CASE?
Not automatically. The CASE expression used in SQL has rules documented in the SQL Language Reference. For example, Oracle’s 12.2 SQL reference specifies compatible result types (with numeric precedence rules for numeric expressions), notes that character comparisons can be collation-sensitive, and gives a maximum of 65,535 arguments for a SQL CASE expression. Those are SQL-expression rules from the 12.2 documentation, not general rules for every PL/SQL CASE statement. Check the reference for the Oracle release and code context you use. See Oracle’s 12.2 SQL CASE Expressions reference.
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