Comparison operators in MySQL - Step-by-Step Execution

Concept Flow - Comparison operators

Start with two values

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Choose comparison operator

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Compare values

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Result: TRUE or FALSE

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Use result in query condition

Comparison operators compare two values and return TRUE or FALSE, which helps filter data in queries.

Execution Sample

MySQL

SELECT * FROM employees WHERE salary > 50000;

This query selects employees whose salary is greater than 50000.

Execution Table

Step	Employee ID	Salary	Condition (salary > 50000)	Result (Include Row)
1	101	48000	48000 > 50000	FALSE
2	102	52000	52000 > 50000	TRUE
3	103	50000	50000 > 50000	FALSE
4	104	75000	75000 > 50000	TRUE
5	105	30000	30000 > 50000	FALSE
Exit	-	-	No more rows	Query ends

💡 All rows checked; query ends after last row.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
Current Employee ID	-	101	102	103	104	105	-
Current Salary	-	48000	52000	50000	75000	30000	-
Condition Result	-	FALSE	TRUE	FALSE	TRUE	FALSE	-

Key Moments - 2 Insights

Why does salary = 50000 return FALSE for the condition salary > 50000?

Because > means strictly greater than, so 50000 is not greater than 50000. See execution_table row 3.

What happens if the condition is FALSE for a row?

That row is not included in the query result. See execution_table rows 1, 3, and 5 where result is FALSE.

Visual Quiz - 3 Questions

Look at the execution_table, what is the condition result for Employee ID 104?

A TRUE

B FALSE

C NULL

D Error

💡 Hint

Check the row with Employee ID 104 in the execution_table under 'Condition Result'.

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

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at the 'Condition Result' column in execution_table for the earliest FALSE.

If the operator changed to salary >= 50000, how would the result for Employee ID 103 change?

A It would remain FALSE

B It would become TRUE

C It would cause an error

D It would be NULL

💡 Hint

Check the difference between > and >= operators in the key_moments section.

Concept Snapshot

Comparison operators compare two values and return TRUE or FALSE.
Common operators: =, !=, <, >, <=, >=.
Used in WHERE clauses to filter rows.
Example: salary > 50000 selects rows with salary greater than 50000.
Equal (=) checks exact match; greater than (>) checks if left is bigger.
Results control which rows appear in query output.

Full Transcript

Comparison operators in SQL compare two values and return TRUE or FALSE. This helps decide which rows to include in query results. For example, the operator > means 'greater than'. If we write WHERE salary > 50000, only employees with salary more than 50000 are selected. In the example, employee with salary 48000 is excluded because 48000 is not greater than 50000. Employee with salary 52000 is included because 52000 is greater than 50000. The operator = means equal, and >= means greater than or equal. Understanding these operators helps filter data effectively.