FETCH FIRST for SQL standard pagination in PostgreSQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the SQL clause FETCH FIRST n ROWS ONLY do?

It limits the query result to return only the first n rows from the result set.

intermediate

How is FETCH FIRST different from LIMIT in PostgreSQL?

FETCH FIRST is part of the SQL standard for pagination, while LIMIT is PostgreSQL-specific. Both limit rows returned, but FETCH FIRST improves portability across databases.

beginner

Write a SQL query to get the first 5 rows from a table named employees using FETCH FIRST.

SELECT * FROM employees FETCH FIRST 5 ROWS ONLY;

intermediate

Can FETCH FIRST be combined with OFFSET for pagination? How?

Yes. Use OFFSET to skip rows, then FETCH FIRST to limit rows returned. Example: SELECT * FROM table OFFSET 10 FETCH FIRST 5 ROWS ONLY; fetches rows 11 to 15.

beginner

Is ROWS keyword mandatory in FETCH FIRST n ROWS ONLY?

No, ROWS is optional. You can write FETCH FIRST 5 ROWS ONLY or FETCH FIRST 5 ONLY. Both work the same.

What does FETCH FIRST 10 ROWS ONLY do in a SQL query?

A Skips the first 10 rows

B Returns all rows except the first 10

C Returns the first 10 rows of the result set

D Deletes the first 10 rows

The clause limits the output to only the first 10 rows.

Which clause is used to skip rows before fetching in SQL pagination?

A OFFSET

B LIMIT

C WHERE

D FETCH FIRST

OFFSET skips a specified number of rows before returning results.

Is FETCH FIRST part of the SQL standard or PostgreSQL-specific?

A Oracle-specific

B PostgreSQL-specific

C MySQL-specific

D SQL standard

FETCH FIRST is part of the SQL standard for pagination.

Which of these is a valid way to limit rows using FETCH FIRST?

A FETCH FIRST ONLY 5 ROWS

B FETCH FIRST 5 ROWS ONLY

C FETCH 5 ROWS FIRST ONLY

D FIRST FETCH 5 ROWS ONLY

The correct syntax is FETCH FIRST 5 ROWS ONLY.

How would you fetch rows 21 to 30 from a table using OFFSET and FETCH FIRST?

A OFFSET 20 FETCH FIRST 10 ROWS ONLY

B OFFSET 10 FETCH FIRST 20 ROWS ONLY

C FETCH FIRST 10 ROWS ONLY OFFSET 20

D LIMIT 10 OFFSET 20

Skip 20 rows, then fetch next 10 rows to get rows 21 to 30.

Explain how to use FETCH FIRST and OFFSET together for pagination in SQL.

Think about skipping some rows and then taking a limited number.

Describe the benefits of using FETCH FIRST over database-specific clauses like LIMIT.

Consider compatibility and standards.

Practice

1. What does the SQL clause FETCH FIRST 5 ROWS ONLY do in a query?

easy

A. Limits the query result to only the first 5 rows.

B. Skips the first 5 rows and returns the rest.

C. Returns all rows except the first 5.

D. Sorts the rows by the first 5 columns.

Solution

1. Step 1: Understand FETCH FIRST clause

   The clause FETCH FIRST 5 ROWS ONLY limits the number of rows returned by the query to 5.

2. Step 2: Effect on query result

   This means only the first 5 rows from the result set will be returned, no more.

3. Final Answer:

   Limits the query result to only the first 5 rows. -> Option A

4. Quick Check:

   FETCH FIRST limits rows = A [OK]

Hint: FETCH FIRST means limit rows returned, not skip [OK]

Common Mistakes:

• Confusing FETCH FIRST with OFFSET
• Thinking FETCH FIRST sorts rows automatically
• Assuming FETCH FIRST removes rows instead of limiting

2. Which of the following is the correct syntax to get the first 10 rows from a table named employees in PostgreSQL?

easy

A. SELECT * FROM employees FETCH 10 ROWS;

B. SELECT * FROM employees FETCH FIRST 10 ROWS ONLY;

C. SELECT * FROM employees LIMIT FIRST 10;

D. SELECT * FROM employees TOP 10;

Solution

1. Step 1: Recall correct FETCH FIRST syntax

   The standard SQL syntax to limit rows is FETCH FIRST n ROWS ONLY. PostgreSQL supports this.

2. Step 2: Check each option

   SELECT * FROM employees FETCH FIRST 10 ROWS ONLY; uses correct syntax. Options A, B, and D are invalid in PostgreSQL.

3. Final Answer:

   SELECT * FROM employees FETCH FIRST 10 ROWS ONLY; -> Option B

4. Quick Check:

   Correct FETCH FIRST syntax = C [OK]

Hint: Use FETCH FIRST n ROWS ONLY for standard limit [OK]

Common Mistakes:

• Using LIMIT FIRST instead of FETCH FIRST
• Using TOP keyword which is SQL Server syntax
• Omitting ROWS ONLY after FETCH FIRST

3. Given the table products with columns id and price, what will this query return?

SELECT id FROM products ORDER BY price DESC FETCH FIRST 3 ROWS ONLY;

medium

A. All products sorted by price descending.

B. The 3 products with the lowest prices.

C. The 3 products with the highest prices.

D. Syntax error due to FETCH FIRST usage.

Solution

1. Step 1: Analyze ORDER BY clause

   The query orders products by price in descending order, so highest prices come first.

2. Step 2: Apply FETCH FIRST 3 ROWS ONLY

   This limits the output to only the first 3 rows after sorting, i.e., top 3 highest priced products.

3. Final Answer:

   The 3 products with the highest prices. -> Option C

4. Quick Check:

   ORDER BY DESC + FETCH FIRST = top rows [OK]

Hint: ORDER BY DESC + FETCH FIRST = top N highest [OK]

Common Mistakes:

• Ignoring ORDER BY and thinking it returns random rows
• Confusing DESC with ASC order
• Assuming FETCH FIRST causes syntax error

4. Identify the error in this query:

SELECT name FROM customers FETCH FIRST 5 ROWS;

medium

A. Missing ORDER BY clause before FETCH FIRST.

B. No error; query is valid.

C. FETCH FIRST cannot be used without OFFSET.

D. Incorrect FETCH FIRST syntax; missing 'ONLY'.

Solution

1. Step 1: Check FETCH FIRST syntax

   The correct syntax requires ROWS ONLY after the number, so it should be FETCH FIRST 5 ROWS ONLY.

2. Step 2: Verify other parts

   ORDER BY is recommended but not mandatory. OFFSET is not required. So the error is missing 'ONLY'.

3. Final Answer:

   Incorrect FETCH FIRST syntax; missing 'ONLY'. -> Option D

4. Quick Check:

   FETCH FIRST needs ROWS ONLY [OK]

Hint: FETCH FIRST must end with ROWS ONLY [OK]

Common Mistakes:

• Omitting 'ONLY' after FETCH FIRST clause
• Thinking ORDER BY is mandatory with FETCH FIRST
• Confusing FETCH FIRST with OFFSET usage

5. You want to show page 3 of a product list with 10 items per page, sorted by created_at ascending. Which query correctly uses FETCH FIRST and OFFSET for this pagination?

hard

A. SELECT * FROM products ORDER BY created_at ASC OFFSET 20 ROWS FETCH FIRST 10 ROWS ONLY;

B. SELECT * FROM products ORDER BY created_at ASC FETCH FIRST 10 ROWS OFFSET 20 ROWS ONLY;

C. SELECT * FROM products ORDER BY created_at ASC FETCH FIRST 30 ROWS ONLY;

D. SELECT * FROM products ORDER BY created_at ASC OFFSET 10 ROWS FETCH FIRST 10 ROWS ONLY;

Solution

1. Step 1: Calculate OFFSET for page 3

   Each page has 10 items, so page 3 starts at row 21. OFFSET is zero-based, so OFFSET = (3-1)*10 = 20.

2. Step 2: Use FETCH FIRST to limit rows per page

   FETCH FIRST 10 ROWS ONLY limits the result to 10 rows for the page.

3. Step 3: Check query syntax order

   OFFSET must come before FETCH FIRST. SELECT * FROM products ORDER BY created_at ASC OFFSET 20 ROWS FETCH FIRST 10 ROWS ONLY; correctly orders OFFSET then FETCH FIRST.

4. Final Answer:

   SELECT * FROM products ORDER BY created_at ASC OFFSET 20 ROWS FETCH FIRST 10 ROWS ONLY; -> Option A

5. Quick Check:

   OFFSET before FETCH FIRST for pagination [OK]

Hint: OFFSET = (page-1)*size; FETCH FIRST = page size [OK]

Common Mistakes:

• Swapping OFFSET and FETCH FIRST order
• Using FETCH FIRST without OFFSET for pages >1
• Incorrect OFFSET calculation for page number