WHERE with comparison operators in SQL - Step-by-Step Execution

Concept Flow - WHERE with comparison operators

Start Query

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Read FROM table

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Apply WHERE condition

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Evaluate comparison operator

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Row matches?

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Include row

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Return filtered rows

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End Query

The query reads the table, applies the WHERE condition using comparison operators to each row, includes rows that match, excludes others, and returns the filtered result.

Execution Sample

SQL

SELECT * FROM employees WHERE salary > 50000;

This query selects all employees whose salary is greater than 50000.

Execution Table

Step	Row ID	salary	Condition (salary > 50000)	Include Row?
1	1	48000	48000 > 50000 = False	No
2	2	52000	52000 > 50000 = True	Yes
3	3	50000	50000 > 50000 = False	No
4	4	75000	75000 > 50000 = True	Yes
5	5	30000	30000 > 50000 = False	No
6	6	60000	60000 > 50000 = True	Yes
Exit	-	-	No more rows to check	-

💡 All rows checked; query returns only rows where salary > 50000 is True.

Variable Tracker

Variable	Start	After Row 1	After Row 2	After Row 3	After Row 4	After Row 5	After Row 6	Final
Current Row ID	-	1	2	3	4	5	6	-
Condition Result	-	False	True	False	True	False	True	-
Included Rows	[]	[]	[2]	[2]	[2,4]	[2,4]	[2,4]	[2,4,6]

Key Moments - 2 Insights

Why is the row with salary 50000 not included even though it equals 50000?

Because the condition uses '>' (greater than), which excludes values equal to 50000. Only values strictly greater than 50000 pass, as shown in execution_table rows 3 and 4.

What happens if the condition is false for a row?

The row is excluded from the result. For example, row 1 with salary 48000 fails the condition and is not included, as seen in execution_table step 1.

Visual Quiz - 3 Questions

Look at the execution_table, which row is the first to be included in the result?

A Row 1

B Row 2

C Row 3

D Row 5

💡 Hint

Check the 'Include Row?' column in execution_table for the first 'Yes'.

At which step does the condition 'salary > 50000' become false for the first time?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Condition (salary > 50000)' column in execution_table for the first 'False'.

If the condition changed to 'salary >= 50000', which row would be included that was previously excluded?

A Row with salary 48000

B Row with salary 30000

C Row with salary 50000

D Row with salary 60000

💡 Hint

Check which row had salary exactly 50000 and was excluded before in execution_table.

Concept Snapshot

WHERE clause filters rows using comparison operators.
Syntax: WHERE column operator value
Common operators: =, >, <, >=, <=, <>
Only rows meeting the condition are returned.
Comparison is done row by row.

Full Transcript

This visual execution shows how the SQL WHERE clause works with comparison operators. The query reads each row from the employees table and checks if the salary is greater than 50000. For each row, the condition is evaluated: if true, the row is included in the result; if false, it is excluded. The execution table lists each row's salary, the condition result, and whether the row is included. The variable tracker shows how the current row and included rows change step by step. Key moments clarify why equal values are excluded with '>' and what happens when the condition is false. The quiz tests understanding by asking about specific steps and effects of changing the condition. This helps beginners see exactly how filtering works in SQL queries.