IF-ELSIF-ELSE control flow in PostgreSQL - Step-by-Step Execution

Concept Flow - IF-ELSIF-ELSE control flow

Start

↓

Check IF condition

Yes| No↓

Check ELSIF condition

Yes| No↓

Execute ELSE block

↓

End

The flow checks the IF condition first; if false, it checks ELSIF conditions in order; if none match, it executes ELSE block if present.

Execution Sample

PostgreSQL

DO $$
BEGIN
  IF 3 > 5 THEN
    RAISE NOTICE 'IF block';
  ELSIF 3 = 3 THEN
    RAISE NOTICE 'ELSIF block';
  ELSE
    RAISE NOTICE 'ELSE block';
  END IF;
END $$;

This code checks conditions in order and prints which block runs based on the first true condition.

Execution Table

Step	Condition Checked	Result	Branch Taken	Output
1	3 > 5	False	Skip IF block
2	3 = 3	True	Execute ELSIF block	ELSIF block
3	ELSE	Skipped	No
4	End IF	N/A	Exit control flow

💡 Condition 3 = 3 is True, so ELSIF block runs and control flow ends.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
Condition Result	N/A	False	True	True
Output	None	None	'ELSIF block'	'ELSIF block'

Key Moments - 2 Insights

Why does the ELSE block not run even though IF is false?

Because the ELSIF condition is true (see execution_table row 2), the control flow executes the ELSIF block and skips ELSE.

What happens if all IF and ELSIF conditions are false?

The ELSE block runs as a fallback (not shown in this trace), ensuring some code executes if no conditions match.

Visual Quiz - 3 Questions

Look at the execution table, what is the result of the first condition checked?

A True

B False

C Skipped

D Error

💡 Hint

Check the 'Condition Checked' and 'Result' columns in row 1 of the execution_table.

At which step does the control flow decide which block to execute?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Branch Taken' and 'Output' columns in the execution_table to see when execution happens.

If the ELSIF condition was false, which block would run next?

A IF block

B ELSIF block again

C ELSE block

D No block runs

💡 Hint

Refer to the concept_flow and execution_table rows 2 and 3 to understand fallback behavior.

Concept Snapshot

IF-ELSIF-ELSE syntax:
IF condition THEN
  -- code
ELSIF condition THEN
  -- code
ELSE
  -- code
END IF;

Checks conditions in order; runs first true block; ELSE runs if none true.

Full Transcript

This example shows how PostgreSQL IF-ELSIF-ELSE control flow works. First, the IF condition is checked. If false, the ELSIF condition is checked. If ELSIF is true, its block runs and ELSE is skipped. If all conditions are false, ELSE runs. The execution table traces each step, showing condition results and which block executes. Variables track condition results and output messages. Key moments clarify why ELSE may not run and what happens if all conditions fail. The quiz tests understanding of condition results and flow decisions.