LIMIT clause behavior in SQL - Step-by-Step Execution

Concept Flow - LIMIT clause behavior

Start Query Execution

↓

Retrieve All Rows

↓

Apply LIMIT Clause

↓

Return Limited Rows

↓

End Query Execution

The database runs the query, fetches all matching rows, then applies the LIMIT clause to return only the specified number of rows.

Execution Sample

SQL

SELECT * FROM employees LIMIT 3;

This query fetches all employees but returns only the first 3 rows.

Execution Table

Step	Action	Rows Retrieved	LIMIT Value	Rows Returned
1	Start query execution	0	3	0
2	Retrieve all matching rows	5	3	0
3	Apply LIMIT clause	5	3	3
4	Return limited rows	5	3	3
5	End query execution	5	3	3

💡 LIMIT 3 restricts output to first 3 rows even though 5 rows matched

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
Rows Retrieved	0	5	5	5
Rows Returned	0	0	3	3
LIMIT Value	3	3	3	3

Key Moments - 2 Insights

Why does the query return fewer rows than exist in the table?

Because the LIMIT clause restricts the number of rows returned to the specified value, as shown in execution_table step 3 where Rows Returned changes from 0 to 3.

Does LIMIT affect how many rows the database searches through?

No, the database retrieves all matching rows first (step 2), then applies LIMIT to reduce the output (step 3).

Visual Quiz - 3 Questions

Look at the execution table, how many rows are retrieved before applying LIMIT?

A 3

B 5

C 0

D All rows in the database

💡 Hint

Check the 'Rows Retrieved' column at step 2 in the execution_table.

At which step does the number of rows returned change from 0 to 3?

A Step 3

B Step 2

C Step 1

D Step 5

💡 Hint

Look at the 'Rows Returned' column in execution_table rows.

If LIMIT was changed to 5, how would the 'Rows Returned' value change at step 3?

A It would be 3

B It would be 0

C It would be 5

D It would be more than 5

💡 Hint

Refer to the LIMIT Value and Rows Returned columns in variable_tracker.

Concept Snapshot

LIMIT clause restricts the number of rows returned by a query.
Syntax: SELECT * FROM table LIMIT number;
The database fetches all matching rows first, then returns only the first 'number' rows.
Useful to preview or paginate results.
If LIMIT exceeds available rows, all rows are returned.

Full Transcript

The LIMIT clause in SQL controls how many rows a query returns. When a query runs, the database first finds all rows that match the query conditions. Then, it applies the LIMIT clause to return only the specified number of rows. For example, if LIMIT 3 is used, only the first 3 rows are returned even if more rows match. This helps to limit output size and is useful for pagination or previews. The execution table shows that all rows are retrieved first, then limited before returning results.

Practice

1. What does the LIMIT clause do in an SQL query?

easy

A. It restricts the number of rows returned by the query.

B. It sorts the rows in ascending order.

C. It groups rows based on a column.

D. It deletes rows from the table.

Solution

1. Step 1: Understand the purpose of LIMIT

   The LIMIT clause is used to restrict the number of rows returned by a query.

2. Step 2: Compare with other options

   Sorting is done by ORDER BY, grouping by GROUP BY, and deleting by DELETE statement, not LIMIT.

3. Final Answer:

   It restricts the number of rows returned by the query. -> Option A

4. Quick Check:

   LIMIT = restrict rows [OK]

Hint: LIMIT controls how many rows you get back [OK]

Common Mistakes:

• Confusing LIMIT with ORDER BY
• Thinking LIMIT deletes rows
• Mixing LIMIT with GROUP BY

2. Which of the following is the correct syntax to get the first 5 rows from a table named employees?

easy

A. SELECT * FROM employees LIMIT 5;

B. SELECT * FROM employees TOP 5;

C. SELECT * FROM employees FETCH FIRST 5 ROWS;

D. SELECT * FROM employees WHERE LIMIT = 5;

Solution

1. Step 1: Identify correct LIMIT syntax

   The standard SQL syntax to limit rows is using LIMIT followed by the number, e.g., LIMIT 5.

2. Step 2: Check other options

   TOP 5 is SQL Server syntax, FETCH FIRST 5 ROWS is standard SQL but typically requires 'ONLY', and WHERE LIMIT = 5 is invalid.

3. Final Answer:

   SELECT * FROM employees LIMIT 5; -> Option A

4. Quick Check:

   LIMIT 5 = first 5 rows [OK]

Hint: Use LIMIT number after FROM to restrict rows [OK]

Common Mistakes:

• Using TOP instead of LIMIT in standard SQL
• Misplacing LIMIT inside WHERE clause
• Using FETCH without OFFSET incorrectly

3. Given the table products with rows:
id | name
1 | Apple
2 | Banana
3 | Cherry
4 | Date
5 | Elderberry
What is the result of the query:
SELECT name FROM products ORDER BY id DESC LIMIT 3;?

medium

A. ["Apple", "Banana", "Cherry"]

B. ["Elderberry", "Date", "Cherry"]

C. ["Cherry", "Date", "Elderberry"]

D. ["Date", "Elderberry", "Cherry"]

Solution

1. Step 1: Understand ORDER BY id DESC

   Ordering by id descending means rows are sorted from highest id to lowest: 5,4,3,2,1.

2. Step 2: Apply LIMIT 3

   LIMIT 3 returns the first 3 rows after sorting: ids 5,4,3 which correspond to Elderberry, Date, Cherry.

3. Final Answer:

   ["Elderberry", "Date", "Cherry"] -> Option B

4. Quick Check:

   ORDER BY DESC + LIMIT 3 = top 3 highest ids [OK]

Hint: ORDER BY DESC then LIMIT gets top N rows [OK]

Common Mistakes:

• Ignoring ORDER BY and taking first rows as is
• Mixing ascending and descending order
• Confusing LIMIT number with offset

4. What is wrong with this query?
SELECT * FROM orders LIMIT;

medium

A. LIMIT only works with numeric columns.

B. LIMIT cannot be used without ORDER BY.

C. LIMIT must be placed before FROM clause.

D. LIMIT requires a number to specify how many rows to return.

Solution

1. Step 1: Check LIMIT syntax

   LIMIT must be followed by a number indicating how many rows to return.

2. Step 2: Validate other options

   LIMIT can be used without ORDER BY, it comes after FROM, and works on any query regardless of column types.

3. Final Answer:

   LIMIT requires a number to specify how many rows to return. -> Option D

4. Quick Check:

   LIMIT needs a number [OK]

Hint: Always put a number after LIMIT [OK]

Common Mistakes:

• Omitting the number after LIMIT
• Thinking ORDER BY is mandatory with LIMIT
• Placing LIMIT before FROM

5. You want to show page 3 of a product list, showing 10 products per page, ordered by price ascending. Which query correctly uses LIMIT and OFFSET to achieve this?

hard

A. SELECT * FROM products ORDER BY price ASC LIMIT 10 OFFSET 30;

B. SELECT * FROM products ORDER BY price ASC LIMIT 30 OFFSET 10;

C. SELECT * FROM products ORDER BY price ASC LIMIT 10 OFFSET 20;

D. SELECT * FROM products ORDER BY price ASC LIMIT 20 OFFSET 10;

Solution

1. Step 1: Calculate OFFSET for page 3 with 10 rows per page

   Page 1 shows rows 0-9, page 2 shows 10-19, so page 3 starts at offset 20.

2. Step 2: Use LIMIT 10 to get 10 rows for the page

   LIMIT 10 returns 10 rows starting from OFFSET 20.

3. Final Answer:

   SELECT * FROM products ORDER BY price ASC LIMIT 10 OFFSET 20; -> Option C

4. Quick Check:

   Page 3 offset = (3-1)*10 = 20 [OK]

Hint: OFFSET = (page-1)*rows, LIMIT = rows per page [OK]

Common Mistakes:

• Using wrong OFFSET calculation
• Mixing LIMIT and OFFSET values
• Forgetting ORDER BY for consistent paging