Conditional Statements in PL/SQL : Understanding How PL/SQL Makes Decisions Using Simple Logic

Introduction: Why Conditional Statements Matter in PL/SQL

In real life, we constantly make decisions:

• If it is raining, we carry an umbrella

• If marks are above passing, we declare success

• Otherwise, we take a different action

PL/SQL programs work in the same way. They do not execute all statements blindly. Instead, they check conditions and decide what to execute and what to skip.

This decision-making ability is provided by conditional statements.

In PL/SQL, conditional statements allow a program to:

• Compare values

• Check logical conditions

• Execute different blocks of code based on results

Without conditional statements, PL/SQL programs would be static and unintelligent.

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What Is a Conditional Statement in PL/SQL?

A conditional statement is a control structure that allows PL/SQL to:

• Evaluate a condition

• Decide which block of code should execute

In simple words:

Conditional statements tell PL/SQL “Do this only if the condition is true.”

Conditions are usually formed using:

• Relational operators (=, <, >, <=, >=, <>)

• Logical operators (AND, OR, NOT)

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Types of Conditional Statements in PL/SQL

PL/SQL provides the following conditional statements:

1. IF statement

2. IF–THEN statement

3. IF–THEN–ELSE statement

4. Nested IF–THEN–ELSE

5. ELSIF ladder

6. CASE statement

   • Simple CASE

   • Searched CASE

Each one is explained deeply and clearly below.

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1. IF Statement in PL/SQL (Basic Decision Making)

Concept Explanation

The IF statement checks a condition and executes a block only when the condition is true.

If the condition is false, PL/SQL simply skips the block.

This is the simplest form of decision making.

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Syntax

IF condition THEN
   statements;
END IF;

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Real-Life Example

Situation:

If a person is above 18 years, allow them to vote.

Logic:

• Condition → age ≥ 18

• Action → allow voting

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PL/SQL Example

DECLARE
   age NUMBER := 20;
BEGIN
   IF age >= 18 THEN
      DBMS_OUTPUT.PUT_LINE('Eligible to vote');
   END IF;
END;

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Important Points

• IF executes only when condition is true

• No alternative action exists

• END IF is mandatory

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2. IF–THEN Statement (Single Condition Execution)

Concept Explanation

The IF–THEN statement is used when:

• You want to check one condition

• You want to perform one specific action

This is commonly used for validation checks.

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Real-Life Example

Situation:

If balance is less than minimum, display warning.

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PL/SQL Example

DECLARE
   balance NUMBER := 800;
BEGIN
   IF balance < 1000 THEN
      DBMS_OUTPUT.PUT_LINE('Low balance warning');
   END IF;
END;

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When to Use IF–THEN

• Checking eligibility

• Validating input

• Displaying warnings

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3. IF–THEN–ELSE Statement (Two-Way Decision)

Concept Explanation

The IF–THEN–ELSE statement allows PL/SQL to choose between two alternatives.

• If condition is true → IF block executes

• If condition is false → ELSE block executes

This ensures one block always runs.

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Syntax

IF condition THEN
   statements;
ELSE
   statements;
END IF;

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Real-Life Example

Situation:

If exam result is pass, display congratulations; otherwise, display retry message.

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PL/SQL Example

DECLARE
   marks NUMBER := 45;
BEGIN
   IF marks >= 50 THEN
      DBMS_OUTPUT.PUT_LINE('You passed the exam');
   ELSE
      DBMS_OUTPUT.PUT_LINE('You failed the exam');
   END IF;
END;

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Key Understanding

• Only one block executes

• ELSE handles the false condition

• Useful for binary decisions

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4. Nested IF–THEN–ELSE (Multiple Levels of Decision)

Concept Explanation

A nested IF means placing one IF statement inside another IF or ELSE block.

This is used when:

• Decisions depend on previous decisions

• Conditions are hierarchical

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Real-Life Example

Situation:

If student passed:

• If marks ≥ 75 → distinction

• Else → pass

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PL/SQL Example

DECLARE
   marks NUMBER := 78;
BEGIN
   IF marks >= 50 THEN
      IF marks >= 75 THEN
         DBMS_OUTPUT.PUT_LINE('Passed with distinction');
      ELSE
         DBMS_OUTPUT.PUT_LINE('Passed');
      END IF;
   ELSE
      DBMS_OUTPUT.PUT_LINE('Failed');
   END IF;
END;

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Important Clarification

• Nested IF increases logical depth

• Should be used carefully to avoid complexity

• Indentation improves readability

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5. ELSIF Ladder (Multiple Conditions Handling)

Concept Explanation

The ELSIF ladder is used when there are multiple conditions, and only one should execute.

PL/SQL checks conditions:

• From top to bottom

• Stops at the first true condition

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Syntax

IF condition1 THEN
   statements;
ELSIF condition2 THEN
   statements;
ELSIF condition3 THEN
   statements;
ELSE
   statements;
END IF;

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Real-Life Example

Situation:

Grade calculation based on marks.

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PL/SQL Example

DECLARE
   marks NUMBER := 82;
BEGIN
   IF marks >= 90 THEN
      DBMS_OUTPUT.PUT_LINE('Grade A');
   ELSIF marks >= 75 THEN
      DBMS_OUTPUT.PUT_LINE('Grade B');
   ELSIF marks >= 50 THEN
      DBMS_OUTPUT.PUT_LINE('Grade C');
   ELSE
      DBMS_OUTPUT.PUT_LINE('Fail');
   END IF;
END;

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Why ELSIF Is Better Than Nested IF

• Cleaner logic

• Easier to read

• Better performance

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6. CASE Statement in PL/SQL (Structured Decision Making)

Concept Explanation

The CASE statement is used when:

• Multiple conditions are based on one expression

• Code clarity is important

CASE is often more readable than long IF–ELSIF ladders.

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6.1 Simple CASE Statement

Syntax

CASE expression
   WHEN value1 THEN statements;
   WHEN value2 THEN statements;
   ELSE statements;
END CASE;

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Real-Life Example

Situation:

Menu-based program.

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PL/SQL Example

DECLARE
   choice NUMBER := 2;
BEGIN
   CASE choice
      WHEN 1 THEN DBMS_OUTPUT.PUT_LINE('Addition');
      WHEN 2 THEN DBMS_OUTPUT.PUT_LINE('Subtraction');
      WHEN 3 THEN DBMS_OUTPUT.PUT_LINE('Multiplication');
      ELSE DBMS_OUTPUT.PUT_LINE('Invalid choice');
   END CASE;
END;

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6.2 Searched CASE Statement

Concept Explanation

The searched CASE allows conditions instead of fixed values.

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Syntax

CASE
   WHEN condition1 THEN statements;
   WHEN condition2 THEN statements;
   ELSE statements;
END CASE;

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Real-Life Example

Salary bonus calculation.

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PL/SQL Example

DECLARE
   salary NUMBER := 45000;
BEGIN
   CASE
      WHEN salary >= 60000 THEN DBMS_OUTPUT.PUT_LINE('High bonus');
      WHEN salary >= 40000 THEN DBMS_OUTPUT.PUT_LINE('Medium bonus');
      ELSE DBMS_OUTPUT.PUT_LINE('Low bonus');
   END CASE;
END;

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Difference Between IF–ELSIF and CASE

IF–ELSIF	CASE
More flexible	More structured
Can be lengthy	Cleaner syntax
Logical conditions	Expression-based

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Common Mistakes Students Make (Important)

• Forgetting END IF

• Using = instead of :=

• Missing ELSIF spelling

• Not enabling DBMS_OUTPUT

• Overusing nested IF

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Final Conclusion

Conditional statements are the decision-making backbone of PL/SQL.

They transform a static block into an intelligent program that reacts to data and conditions.

By mastering:

• IF

• IF–ELSE

• ELSIF

• CASE

You gain the ability to write real-world PL/SQL logic used in:

• Banking systems

• Payroll processing

• Student management

• Business applications