TOP vs LIMIT across databases in SQL - Quick Revision & Key Differences

Recall & Review

beginner

What does the TOP keyword do in SQL?

TOP limits the number of rows returned by a query, commonly used in SQL Server and MS Access.

beginner

What is the purpose of the LIMIT clause in SQL?

LIMIT restricts the number of rows returned by a query, commonly used in MySQL, PostgreSQL, and SQLite.

beginner

How do you write a query to get the first 5 rows in SQL Server?

Use: SELECT TOP 5 * FROM table_name;

beginner

How do you write a query to get the first 5 rows in MySQL?

Use: SELECT * FROM table_name LIMIT 5;

intermediate

Can TOP and LIMIT be used interchangeably in all SQL databases?

No. TOP is mainly for SQL Server and MS Access, while LIMIT is for MySQL, PostgreSQL, and SQLite. They are not interchangeable across all databases.

Which SQL keyword is used to limit rows in MySQL?

A ROWNUM

B TOP

C LIMIT

D FETCH

MySQL uses LIMIT to restrict the number of rows returned.

How do you get the first 10 rows in SQL Server?

A SELECT TOP 10 * FROM table;

B SELECT * FROM table WHERE ROWNUM <= 10;

C SELECT * FROM table FETCH FIRST 10 ROWS;

D SELECT * FROM table LIMIT 10;

SQL Server uses TOP to limit rows, so SELECT TOP 10 * FROM table; is correct.

Which database commonly uses the LIMIT clause?

A MySQL

B SQL Server

C Oracle

D MS Access

MySQL commonly uses LIMIT to restrict rows.

Is the following query valid in PostgreSQL? SELECT TOP 5 * FROM users;

A Only if LIMIT is also used

B Yes

C Only with a special extension

D No

PostgreSQL does not support TOP; it uses LIMIT instead.

Which keyword is NOT used to limit rows in standard SQL?

A TOP

B SELECT

C LIMIT

D FETCH

SELECT is used to retrieve data, not to limit rows.

Explain the difference between TOP and LIMIT in SQL and name which databases commonly use each.

Think about which keyword you use in SQL Server vs MySQL.

Write example queries to get the first 3 rows from a table named 'employees' using both TOP and LIMIT.

Remember TOP goes after SELECT, LIMIT goes at the end.

Practice

1. Which SQL clause is used to limit the number of rows returned in SQL Server?

easy

A. LIMIT

B. TOP

C. FETCH FIRST

D. ROWNUM

Solution

1. Step 1: Understand SQL Server syntax

   SQL Server uses the TOP clause immediately after SELECT to limit rows.

2. Step 2: Compare with other databases

   Other databases like MySQL and PostgreSQL use LIMIT at the end, not SQL Server.

3. Final Answer:

   TOP -> Option B

4. Quick Check:

   SQL Server = TOP [OK]

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

Common Mistakes:

• Using LIMIT in SQL Server
• Placing TOP at the end of the query
• Confusing FETCH FIRST with TOP

2. Which of the following is the correct syntax to get the first 5 rows in MySQL?

easy

A. SELECT * FROM table_name LIMIT 5;

B. SELECT TOP 5 * FROM table_name;

C. SELECT * FROM table_name FETCH FIRST 5 ROWS;

D. SELECT * FROM table_name WHERE ROWNUM <= 5;

Solution

1. Step 1: Recall MySQL syntax for limiting rows

   MySQL uses LIMIT at the end of the query to restrict rows.

2. Step 2: Check each option

   SELECT * FROM table_name LIMIT 5; uses LIMIT 5 correctly; SELECT TOP 5 * FROM table_name; uses SQL Server syntax; Options C and D are for other databases.

3. Final Answer:

   SELECT * FROM table_name LIMIT 5; -> Option A

4. Quick Check:

   MySQL = LIMIT at end [OK]

Hint: Use LIMIT at the end in MySQL queries [OK]

Common Mistakes:

• Using TOP in MySQL
• Placing LIMIT before FROM
• Using ROWNUM which is Oracle syntax

3. Given the table Employees with columns Id and Name, what will this query return in SQL Server?

SELECT TOP 3 Name FROM Employees ORDER BY Id DESC;

medium

A. The first 3 employees ordered by Id ascending

B. The last 3 employees ordered by Id descending

C. Syntax error due to TOP placement

D. The top 3 employees ordered by Id descending

Solution

1. Step 1: Understand TOP with ORDER BY in SQL Server

   The query selects the top 3 rows after ordering by Id descending, so highest Ids first.

2. Step 2: Analyze the result

   The result is the 3 employees with the highest Id values, ordered descending.

3. Final Answer:

   The top 3 employees ordered by Id descending -> Option D

4. Quick Check:

   TOP 3 + ORDER BY DESC = highest 3 rows [OK]

Hint: TOP limits rows after ORDER BY sorting [OK]

Common Mistakes:

• Thinking TOP returns first rows before ORDER BY
• Confusing ascending and descending order
• Assuming syntax error with TOP

4. Identify the error in this PostgreSQL query:

SELECT TOP 10 * FROM Customers;

medium

A. TOP is not valid in PostgreSQL

B. Missing ORDER BY clause

C. LIMIT should be placed before FROM

D. Syntax is correct

Solution

1. Step 1: Recall PostgreSQL syntax for limiting rows

   PostgreSQL uses LIMIT at the end, not TOP.

2. Step 2: Check the query

   The query uses TOP 10, which is invalid syntax in PostgreSQL and causes an error.

3. Final Answer:

   TOP is not valid in PostgreSQL -> Option A

4. Quick Check:

   PostgreSQL = LIMIT, not TOP [OK]

Hint: PostgreSQL uses LIMIT, not TOP [OK]

Common Mistakes:

• Using TOP in PostgreSQL
• Placing LIMIT before FROM
• Assuming ORDER BY is mandatory for LIMIT

5. You want to write a query that returns the top 5 highest salaries from an Employees table. Which query works correctly in both SQL Server and MySQL?

hard

A. Use UNION of SQL Server and MySQL queries

B. SELECT Salary FROM Employees ORDER BY Salary DESC LIMIT 5;

C. SELECT Salary FROM Employees ORDER BY Salary DESC FETCH FIRST 5 ROWS ONLY;

D. SELECT TOP 5 Salary FROM Employees ORDER BY Salary DESC;

Solution

1. Step 1: Understand syntax differences

   SQL Server uses TOP after SELECT; MySQL uses LIMIT at the end.

2. Step 2: Check each option for cross-DB compatibility

   SELECT TOP 5 Salary FROM Employees ORDER BY Salary DESC; works only in SQL Server; SELECT Salary FROM Employees ORDER BY Salary DESC LIMIT 5; only in MySQL; Use UNION of SQL Server and MySQL queries doesn't provide a single query that parses in both; SELECT Salary FROM Employees ORDER BY Salary DESC FETCH FIRST 5 ROWS ONLY; is standard SQL supported by both.

3. Final Answer:

   SELECT Salary FROM Employees ORDER BY Salary DESC FETCH FIRST 5 ROWS ONLY; -> Option C

4. Quick Check:

   FETCH FIRST = cross-DB standard [OK]

Hint: Use FETCH FIRST ROWS ONLY for cross-DB compatibility [OK]

Common Mistakes:

• Using LIMIT (MySQL only)
• Using TOP (SQL Server only)
• Proposing UNION which fails parsing