WHERE with OR operator in SQL - Step-by-Step Execution

Concept Flow - WHERE with OR operator

Start Query

↓

Scan Table Rows

↓

Evaluate WHERE Condition

↓

Condition 1 True?

Yes→Include Row

↓

Condition 2 True?

Yes→Include Row

↓

Exclude Row

↓

Return Filtered Rows

↓

End Query

The query scans each row, checks if either condition in the OR is true, includes the row if yes, otherwise excludes it.

Execution Sample

SQL

SELECT * FROM employees
WHERE department = 'Sales' OR salary > 70000;

This query selects employees who are either in the Sales department or have a salary greater than 70000.

Execution Table

Step	Row Data	Condition: department='Sales'	Condition: salary>70000	OR Result	Include Row?
1	{id:1, department:'Sales', salary:65000}	True	False	True	Yes
2	{id:2, department:'HR', salary:72000}	False	True	True	Yes
3	{id:3, department:'IT', salary:60000}	False	False	False	No
4	{id:4, department:'Sales', salary:75000}	True	True	True	Yes
5	{id:5, department:'Marketing', salary:50000}	False	False	False	No
Exit	All rows processed	-	-	-	Query ends

💡 All rows checked; rows included if either condition is true.

Variable Tracker

Variable	Start	After Row 1	After Row 2	After Row 3	After Row 4	After Row 5	Final
department='Sales'	N/A	True	False	False	True	False	N/A
salary>70000	N/A	False	True	False	True	False	N/A
OR Result	N/A	True	True	False	True	False	N/A
Include Row?	N/A	Yes	Yes	No	Yes	No	N/A

Key Moments - 3 Insights

Why does the query include a row if only one of the conditions is true?

Because the OR operator returns true if at least one condition is true, as shown in the execution_table rows 1 and 2 where only one condition is true but the row is included.

What happens if both conditions are false for a row?

The OR result is false, so the row is excluded. This is shown in rows 3 and 5 of the execution_table.

Does the OR operator check both conditions even if the first is true?

In SQL, the OR operator evaluates conditions until it finds one true condition. However, for clarity, the table shows both conditions evaluated for each row.

Visual Quiz - 3 Questions

Look at the execution_table, what is the OR Result for row 3?

A True

B False

C Unknown

D Depends on database

💡 Hint

Check the 'OR Result' column for Step 3 in the execution_table.

At which step does the condition 'salary > 70000' become true for the first time?

A Step 2

B Step 1

C Step 4

D Step 5

💡 Hint

Look at the 'Condition: salary>70000' column in the execution_table.

If the OR operator was replaced with AND, which row(s) would be included?

A Rows 1 and 4

B Rows 2 and 4

C Only Row 4

D All rows

💡 Hint

Check which rows have both conditions true in the execution_table.

Concept Snapshot

WHERE with OR operator:
- Syntax: WHERE condition1 OR condition2
- Returns rows where at least one condition is true
- Evaluates each row's conditions
- Includes row if OR result is true
- Useful for filtering multiple criteria

Full Transcript

This visual execution shows how the SQL WHERE clause with the OR operator works. The query scans each row in the employees table and checks two conditions: if the department is 'Sales' or if the salary is greater than 70000. For each row, it evaluates both conditions and then applies the OR operator. If either condition is true, the row is included in the result. The execution table lists each row's data, condition results, the OR result, and whether the row is included. Key moments clarify why rows with one true condition are included and what happens when both are false. The quiz tests understanding of condition evaluation and the effect of changing OR to AND.