SQL Advanced

The TOP Clause

The TOP clause is used to specify the number of records to return.
The TOP clause can be very useful on large tables with thousands of records. Returning a large number of records can impact on performance.
Note: Not all database systems support the TOP clause.

SQL Server Syntax

SELECT TOP number|percent column_name(s) FROM table_name

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SQL SELECT TOP Equivalent in MySQL and Oracle

MySQL Syntax

SELECT column_name(s) FROM table_name LIMIT number

Example

SELECT * FROM Persons LIMIT 5

Oracle Syntax

SELECT column_name(s) FROM table_name WHERE ROWNUM <= number

Example

SELECT * FROM Persons WHERE ROWNUM <=5

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SQL TOP Example

The "Persons" table:

P_Id	LastName	FirstName	Address	City
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes
3	Pettersen	Kari	Storgt 20	Stavanger
4	Nilsen	Tom	Vingvn 23	Stavanger

Now we want to select only the two first records in the table above.
We use the following SELECT statement:

 

SELECT TOP 2 * FROM Persons

The result-set will look like this:

P_Id	LastName	FirstName	Address	City
1	Hansen	Ola	Timoteivn 10	Sandnes
2	Svendson	Tove	Borgvn 23	Sandnes

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