LIMIT vs TOP vs FETCH FIRST syntax in SQL - Quick Revision & Key Differences

Recall & Review

beginner

What does the LIMIT clause do in SQL?

The LIMIT clause restricts the number of rows returned by a query to a specified number. It is commonly used in MySQL and PostgreSQL.

beginner

How does the TOP keyword work in SQL?

TOP is used in SQL Server to limit the number of rows returned by a query. It appears right after SELECT and specifies how many rows to return.

intermediate

Explain the FETCH FIRST syntax in SQL.

FETCH FIRST is part of the SQL standard and is used to limit the number of rows returned. It is often combined with OFFSET for pagination and supported by databases like DB2, Oracle 12c+, and PostgreSQL.

beginner

Which SQL syntax is specific to SQL Server for limiting rows?

The TOP keyword is specific to SQL Server for limiting the number of rows returned by a query.

intermediate

Match the SQL syntax to its common database: LIMIT, TOP, FETCH FIRST

• LIMIT: MySQL, PostgreSQL
• TOP: SQL Server
• FETCH FIRST: DB2, Oracle 12c+, PostgreSQL

Which SQL clause is used in MySQL to limit the number of rows returned?

A LIMIT

B TOP

C FETCH FIRST

D ROWNUM

LIMIT is the clause used in MySQL to restrict the number of rows returned.

In SQL Server, how do you limit the number of rows returned?

A TOP

B OFFSET

C FETCH FIRST

D LIMIT

TOP is the keyword used in SQL Server to limit rows.

Which syntax is part of the SQL standard and supports pagination with OFFSET?

A TOP

B FETCH FIRST

C LIMIT

D ROWNUM

FETCH FIRST is part of the SQL standard and works with OFFSET for pagination.

Which database commonly uses FETCH FIRST syntax?

A SQLite

B SQL Server

C MySQL

D Oracle 12c+

Oracle 12c+ supports FETCH FIRST syntax.

What is the correct way to limit rows in PostgreSQL?

A TOP 10

B LIMIT 10

C Both B and D

D FETCH FIRST 10 ROWS ONLY

PostgreSQL supports both LIMIT and FETCH FIRST syntax.

Describe the differences between LIMIT, TOP, and FETCH FIRST syntax in SQL.

Think about which databases use each syntax and how they appear in queries.

Explain how you would limit query results in SQL Server versus MySQL.

Focus on the placement of the keywords in the query.

Practice

1. Which SQL clause is used to limit the number of rows returned in a query in MySQL and PostgreSQL?

easy

A. LIMIT

B. TOP

C. FETCH FIRST

D. ROWNUM

Solution

1. Step 1: Identify the database systems mentioned

   MySQL and PostgreSQL use the LIMIT clause to restrict rows.

2. Step 2: Match the clause to the database

   TOP is for SQL Server, FETCH FIRST is for Oracle and others, ROWNUM is Oracle-specific but older style.

3. Final Answer:

   LIMIT -> Option A

4. Quick Check:

   MySQL/PostgreSQL use LIMIT [OK]

Hint: MySQL/PostgreSQL use LIMIT to restrict rows [OK]

Common Mistakes:

• Confusing TOP with LIMIT
• Using FETCH FIRST in MySQL
• Using ROWNUM in PostgreSQL

2. Which of the following is the correct syntax to get the top 5 rows in SQL Server?

easy

A. SELECT * FROM table WHERE ROWNUM <= 5;

B. SELECT * FROM table LIMIT 5;

C. SELECT * FROM table FETCH FIRST 5 ROWS ONLY;

D. SELECT TOP 5 * FROM table;

Solution

1. Step 1: Identify SQL Server syntax for limiting rows

   SQL Server uses TOP n after SELECT to limit rows.

2. Step 2: Check each option

   SELECT * FROM table LIMIT 5; uses LIMIT (MySQL/PostgreSQL), SELECT * FROM table FETCH FIRST 5 ROWS ONLY; uses FETCH FIRST (Oracle), SELECT * FROM table WHERE ROWNUM <= 5; uses ROWNUM (Oracle). Only SELECT TOP 5 * FROM table; is correct for SQL Server.

3. Final Answer:

   SELECT TOP 5 * FROM table; -> Option D

4. Quick Check:

   SQL Server uses TOP [OK]

Hint: TOP goes right after SELECT in SQL Server [OK]

Common Mistakes:

• Using LIMIT in SQL Server
• Placing TOP after FROM
• Using FETCH FIRST in SQL Server

3. Given this query in Oracle:

SELECT * FROM employees FETCH FIRST 3 ROWS ONLY;

What will be the result?

medium

A. Syntax error because FETCH FIRST is not valid in Oracle

B. Returns the first 3 rows from employees

C. Returns all rows because FETCH FIRST is ignored

D. Returns 3 random rows from employees

Solution

1. Step 1: Understand FETCH FIRST in Oracle

   Oracle supports FETCH FIRST n ROWS ONLY to limit rows returned.

2. Step 2: Determine query behavior

   The query returns exactly the first 3 rows from the employees table as ordered by the query (default order if none specified).

3. Final Answer:

   Returns the first 3 rows from employees -> Option B

4. Quick Check:

   Oracle FETCH FIRST limits rows [OK]

Hint: FETCH FIRST limits rows in Oracle [OK]

Common Mistakes:

• Thinking FETCH FIRST causes syntax error in Oracle
• Assuming FETCH FIRST returns random rows
• Believing FETCH FIRST is ignored

4. Identify the error in this SQL Server query:

SELECT * FROM customers FETCH FIRST 10 ROWS ONLY;

medium

A. Should use LIMIT instead of FETCH FIRST

B. Missing ORDER BY clause with FETCH FIRST

C. FETCH FIRST is not supported in SQL Server

D. Syntax is correct, no error

Solution

1. Step 1: Check FETCH FIRST support in SQL Server

   SQL Server does not support FETCH FIRST; it uses TOP instead.

2. Step 2: Analyze other options

   Missing ORDER BY clause with FETCH FIRST is incorrect because FETCH FIRST requires ORDER BY in some databases but SQL Server does not support FETCH FIRST at all. Should use LIMIT instead of FETCH FIRST is wrong because SQL Server uses TOP, not LIMIT. Syntax is correct, no error is false because syntax is invalid.

3. Final Answer:

   FETCH FIRST is not supported in SQL Server -> Option C

4. Quick Check:

   SQL Server uses TOP, not FETCH FIRST [OK]

Hint: SQL Server uses TOP, not FETCH FIRST [OK]

Common Mistakes:

• Using FETCH FIRST in SQL Server
• Confusing LIMIT with FETCH FIRST
• Assuming FETCH FIRST works without ORDER BY

5. You want to write a query that returns the top 10 rows from a table named sales in a database that supports both FETCH FIRST and LIMIT. Which query is correct and why?

Options:
A) SELECT * FROM sales LIMIT 10;
B) SELECT * FROM sales FETCH FIRST 10 ROWS ONLY;
C) SELECT TOP 10 * FROM sales;
D) SELECT * FROM sales WHERE ROWNUM <= 10;

hard

A. Correct if the database supports LIMIT syntax

B. Correct if the database supports FETCH FIRST syntax

C. Correct only in SQL Server

D. Correct only in Oracle with ROWNUM

Solution

1. Step 1: Understand the database supports both FETCH FIRST and LIMIT

   Some modern databases like DB2 or Oracle 12c+ support FETCH FIRST, while others like MySQL use LIMIT.

2. Step 2: Choose the correct syntax for the database

   If the database supports both, FETCH FIRST is the ANSI standard and preferred for portability. LIMIT is not standard SQL. TOP is SQL Server specific, and ROWNUM is Oracle-specific older syntax.

3. Final Answer:

   SELECT * FROM sales FETCH FIRST 10 ROWS ONLY; -> Option A

4. Quick Check:

   FETCH FIRST is ANSI standard for limiting rows [OK]

Hint: Use FETCH FIRST for ANSI standard row limiting [OK]

Common Mistakes:

• Using TOP in non-SQL Server databases
• Assuming LIMIT is standard SQL
• Using ROWNUM outside Oracle