EXIT and CONTINUE Statements in PL/SQL

PL/SQL is Oracle’s procedural extension to SQL, allowing the development of complex database applications. Out of its many features that make it powerful. The control statements

-the means through which the language can control the flow of execution within scripts-are very important. The two key control statements covered in this article are the EXIT Statement and the CONTINUE Statement. They are the basic statements of loop management and condition logic in PL/SQL. We’ll discuss their syntax, usage, examples, and best practice by utilizing tables as support to explain as much as possible.

Understanding Loop Control Statements in PL/SQL

Control statements in PL/SQL are so important to the management of the procedure and function execution flow. They allow a program to change its execution order depending on certain conditions. The EXIT statement allows a loop to terminate early if a condition is met, while the CONTINUE statement allows skipping the rest of the loop’s body for the current iteration.

Table 1: Key PL/SQL Control Statements

Statement	Description
EXIT Statement	Exits a loop before its normal termination.
CONTINUE Statement	Skips the remaining statements in the loop for the current iteration and proceeds to the next iteration.

Control statements are used to enhance the readability and performance of your code. They allow you to apply a complex logic that may depend on the type of data you are working with. In this article, we show what a developer needs to know concerning the use of EXIT and CONTINUE Statements in loops.

The EXIT Statement in PL/SQL

The EXIT STATEMENT enables the breaking of a loop before it has completed normally. This statement can be located anywhere in the loop and thus offers flexibility in which and when loops get terminated. The statement is often used along with conditional expressions to provide a graceful exit according to some preconditions.

Syntax of EXIT Statement

EXIT [WHEN condition];

• condition: This is a boolean expression to determine whether to leave the loop.

Example of EXIT Statement

Let’s take a simple example illustrating the use of the EXIT Statement in a WHILE LOOP for counting numbers up to some number.

Explanation of the Example

In this example:

• We declare a variable v_counter initialized to 1.
• The WHILE LOOP checks if v_counter is less than or equal to 10.
• Within the loop, we print the current value of the counter.
• When v_counter equals 5, the EXIT Statement is executed, causing the loop to terminate early.
• If the condition were never met, the loop would continue until v_counter exceeds 10.

Result of the EXIT Statement

When executed, the output will be:

Counter value: 1
Counter value: 2
Counter value: 3
Counter value: 4
Counter value: 5

The loop stops running once the counter reaches 5, demonstrating how the EXIT Statement effectively breaks the loop at the desired point.

Using CONTINUE Statement in PL/SQL

The CONTINUE Statement is used within loops to skip the current iteration and move on to the next one. This statement is particularly beneficial when certain conditions are met that warrant bypassing the remaining statements in the loop for that iteration.

Syntax of CONTINUE Statement

CONTINUE [loop_label];

• loop_label: An optional identifier for the loop, allowing the CONTINUE Statement to be associated with a specific loop if multiple loops are nested.

Example of CONTINUE Statement

Let’s look at an example that demonstrates the CONTINUE Statement in a FOR LOOP.

DECLARE
    v_counter NUMBER;
BEGIN
    FOR v_counter IN 1 .. 10 LOOP
        IF MOD(v_counter, 2) = 0 THEN
            CONTINUE; -- Skip even numbers
        END IF;
        
        DBMS_OUTPUT.PUT_LINE('Odd number: ' || v_counter);
    END LOOP;
END;

Explanation of the Example

In this example:

• A FOR LOOP iterates from 1 to 10.
• The MOD function checks if the current number (v_counter) is even.
• If v_counter is even, the CONTINUE Statement is executed, skipping the DBMS_OUTPUT.PUT_LINE statement for that iteration.
• If the number is odd, it prints the current number.

Result of the CONTINUE Statement

When executed, the output will be:

Odd number: 1
Odd number: 3
Odd number: 5
Odd number: 7
Odd number: 9

This output demonstrates that only odd numbers are printed, as even numbers are effectively skipped due to the CONTINUE Statement.

Combining EXIT and CONTINUE Statements

The EXIT and CONTINUE Statements can be used together within the same loop to create more complex control flow. This capability allows for intricate logic to be implemented based on multiple conditions.

Example: Combining Both Statements

In the following example, we will see how to use both EXIT and CONTINUE in a WHILE LOOP.

DECLARE
    v_counter NUMBER := 1; -- Initializing the counter
BEGIN
    WHILE v_counter <= 10 LOOP
        IF v_counter = 3 THEN
            v_counter := v_counter + 1; -- Increment before continuing
            CONTINUE; -- Skip the number 3
        ELSIF v_counter = 7 THEN
            EXIT; -- Exit when the counter reaches 7
        END IF;
        
        DBMS_OUTPUT.PUT_LINE('Current number: ' || v_counter);
        v_counter := v_counter + 1; -- Increment the counter
    END LOOP;
END;

Explanation of the Example

In this example:

• The loop iterates from 1 to 10.
• When v_counter equals 3, it increments the counter and executes the CONTINUE Statement, skipping the print statement for that iteration.
• When v_counter reaches 7, the EXIT Statement is triggered, terminating the loop.

Result of Combined Usage

When executed, the output will be:

Current number: 1
Current number: 2
Current number: 4
Current number: 5
Current number: 6

This output shows how the loop avoids printing the number 3 and then comes out with 7 as soon as the loop has cycled through the elements because of both control statements used.

EXIT and CONTINUE Statements Applications

Use Case 1: Validate Data Input

One of the most popular uses for the EXIT Statement is in validation of user input. Where a particular condition fails, the loop can be exited and an error message presented. A simple example demonstrates the application for validating user input:

DECLARE
    v_input NUMBER;
    v_counter NUMBER := 1; -- Initialize the counter
BEGIN
    WHILE v_counter <= 5 LOOP
        -- Simulate user input (for example purposes)
        v_input := DBMS_RANDOM.VALUE(1, 10); 
        
        IF v_input < 5 THEN
            DBMS_OUTPUT.PUT_LINE('Input is too low, exiting...');
            EXIT; -- Exit if the input is less than 5
        END IF;
        
        DBMS_OUTPUT.PUT_LINE('Valid input: ' || v_input);
        v_counter := v_counter + 1; -- Increment counter
    END LOOP;
END;

Use Case 2: Filtering Records

Another practical application is filtering records in a dataset. The CONTINUE Statement can help skip over certain records based on conditions:

DECLARE
    CURSOR c_data IS
        SELECT employee_id, salary FROM employees;
    v_salary employees.salary%TYPE;
BEGIN
    FOR rec IN c_data LOOP
        IF rec.salary < 3000 THEN
            CONTINUE; -- Skip employees with a salary below 3000
        END IF;
        
        DBMS_OUTPUT.PUT_LINE('Employee ID: ' || rec.employee_id || ', Salary: ' || rec.salary);
    END LOOP;
END;

Advantages of EXIT and CONTINUE Statements in PL/SQL

EXIT and CONTINUE statements in PL/SQL offer massive control over the execution of loops. This provides the developers with a number of choices concerning how to interact with loops. They make handling loops much easier and the code more efficient. Here are some of the most significant benefits of using EXIT and CONTINUE in PL/SQL:

1. More Efficient Control Over Loop Flow

The EXIT and CONTINUE statements provide developers with precise control over the loop termination, or continuation. EXIT makes it possible for a loop to end immediately based on a condition, while CONTINUE skips the current iteration, moving on to the next. This flexibility helps manage loop execution much better.

2. Optimal Loop Termination

This way, the EXIT statement can be used for optimization of loops by causing a desired loop to terminate early, skipping any further iterations when a certain condition is reached. This significantly improves performance, particularly in loops handling large amounts of data or complex operations.

3. Simplified Logic

EXIT and CONTINUE make it easy to work with the logic in any loop. Without these statements, programmers would often require more complicated conditions or nested loops to be able to accomplish the same thing. Controlling the termination and iteration of a loop directly makes the logic straightforward and easier to understand.

4. Avoids Infinite Loops

This EXIT statement really comes in very handy in the prevention of infinite loops. Clear definition of an exit condition by developers ensures that a loop terminates properly and does not allow the program to hang, hence making the code safer and reliable.

5. Enhanced Readability

EXIT and CONTINUE may make the code more readable as tracing for the executable flow may be easier to understand. Since exiting or skipping iterations occur clearly, without dependency on complicated conditions, better, cleaner, and maintainable code results.

6. Efficiency in Skipping Unnecessary Iterations

The CONTINUE statement allows developers to bypass unnecessary processing within a loop and jump directly to the next iteration. It can optimize loops by bypassing operations that may not apply to the given condition.

7. Useful for Error Handling

The EXIT statement helps in exiting a loop if an error or unexpected condition occurs, allowing graceful issues handling not causing the program to crash. This increases the robustness of code as loops will be able to handle errors positively.

8. Lesser Number of Nested Loops Needed

EXIT and CONTINUE would sometimes eliminate nested loops by its minimalistic approach to handling loop flow. This would go to mean less complexity in the code and easier to understand logic.

9. Elegant Condition Handling

Both EXIT and CONTINUE allow for flexibility in the conditions that control a loop. For example, the use of dynamic conditions can enforce termination or skipping of loops based on conditions that may change at run time, hence offering flexibility to adapt to different needs of either data or logic.

10. Improved Performance for Large Datasets

By allowing loops to exit or skip iterations early, both **EXIT** and **CONTINUE** can reduce the number of unnecessary iterations, leading to faster processing times, especially when handling large datasets or complex operations.

Disadvantages of EXIT and CONTINUE Statements in PL/SQL

Although the EXIT and CONTINUE statements within PL/SQL are pretty strong and power the control over loops, there are a couple of disadvantages. A couple of them may have adverse effects on the readability or maintenance or performance if certain care is not taken. Some of the major disadvantages attributable to the use of EXIT and CONTINUE in PL/SQL are as follows:

1. Lost Readability

The high frequency of EXIT or CONTINUE statements can make it difficult to understand the flow of a program. Additionally, when there are many exit or continue points in loops, developers would find tracing their logic quite challenging, hence less readable and harder to trace.

2. Adding Complexity

Too much use of EXIT and CONTINUE can make the logic more complicated than it has to be. Many conditions controlling either how a loop terminates or skips iterations can make hard to understand which path the program was actually intended to use, thus increasing the chance that errors may occur and confusion arise during debugging.

3. Unintended Side Effects

If EXIT and CONTINUE statements are not properly under control, then it may cause unwanted side effects. As an illustration, missing important parts of any loop or premature termination of any loop causes incomplete processing of any data or skipped operations that would have occurred otherwise.

4. Missing Critical Logic

The CONTINUE statement is a good way to avoid iterations but will sometimes skip logic that is critical within a loop. If the critical operations are placed after the CONTINUE statement, it will not be executed and, thus may result in some kind of logic flaw or incomplete processing.

5. Less Clear Exit Strategy

While EXIT is a very clear way to control loop termination, many EXIT statements or statements in poorly placed locations obscure the strategy used to exit the loop. Without comments, someone else might find it difficult to understand why a given loop terminates at a particular point once they encounter an early EXIT without comments.

6. May Cause Poor Performance

While it sometimes leads to an improvement in performance, it then triggers inefficiencies that occur when one uses exit or continue wrongly. Such a scenario can be such that the loop continues skipping some number of iterations without even processing the data. Then, the logic may still be consuming some system resources but not meeting the output as expected.

7. Nested Loops Insecurities

This has a high potential for causing mistakes and unintended behavior when nested loops are used. Because the exit and continue statements can be nondoceptive of which loop is actually being exited or continued, it becomes particularly difficult to follow what happens once the control structure becomes deeply nested, leading to bugs that are hard to trace.

8. Lack of Fine-Grained Control

The EXIT statement definitely terminates the loop completely, but in certain scenarios, developers might need a little more granularity than this, or maybe selectively continuing with some parts of the loop. Such a requirement makes EXIT less flexible in complicated scenarios where partial loop termination might be needed.

9. Prone to Inconsistent Error Handling

EXIT or CONTINUE statements without proper error handling can bypass the control flow and might skip the code for error management. This results in unhandled exceptions or incompletely resolved paths that lead to inconsistent application behaviors.

10. May Miss Optimization Opportunities

While the use of EXIT and CONTINUE statements can hide opportunities for optimizing loop performance, it makes loops with multiple exit points, which blur the control flow following a loop, not easy to optimize database queries or database operations, hence sometimes resulting in inefficient execution plans.