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SQL TOP, LIMIT, FETCH FIRST or ROWNUM Clause
In SQL, the TOP, LIMIT, FETCH FIRST, and ROWNUM clauses are used to limit the number of rows returned by a query. The specific clause used depends on the SQL database management system (DBMS) you're working with. Here are examples and outputs for each of these clauses across different DBMS:
1. TOP Clause (SQL Server)
Example:
SELECT TOP 5 *
FROM Employees
ORDER BY Salary DESC;
Output:
This query returns the top 5 employees with the highest salaries from the Employees table.
2. LIMIT Clause (MySQL, PostgreSQL, SQLite)
Example:
SELECT *
FROM Employees
ORDER BY Salary DESC
LIMIT 5;
Output:
This query returns the top 5 employees with the highest salaries from the Employees table.
3. FETCH FIRST Clause (DB2, Oracle 12c and later)
Example:
SELECT *
FROM Employees
ORDER BY Salary DESC
FETCH FIRST 5 ROWS ONLY;
Output:
This query returns the top 5 employees with the highest salaries from the Employees table.
4. ROWNUM Clause (Oracle)
Example:
SELECT *
FROM (
SELECT *
FROM Employees
ORDER BY Salary DESC
)
WHERE ROWNUM <= 5;
Output:
This query returns the top 5 employees with the highest salaries from the Employees table.
Summary
- SQL Server: Use
TOPclause. - MySQL, PostgreSQL, SQLite: Use
LIMITclause. - DB2, Oracle 12c+: Use
FETCH FIRSTclause. - Oracle (any version): Use
ROWNUMclause.
Each clause is designed to perform the same task of limiting the number of rows returned, but they are syntactically different to accommodate the respective SQL DBMS.
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