Master SQL LIMIT clause: Control the number of rows in a query

SQL LIMIT clause: Control the number of rows in the query result

The LIMIT clause in SQL is used to limit the number of rows returned by a query. This is very useful when processing large data sets, paginated displays and test data, and can effectively improve query efficiency.

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grammar

Basic syntax:

 <code class="language-sql">SELECT column1, column2,... FROM table_name LIMIT number_of_rows;</code>

number_of_rows : Specifies the number of rows returned.

Syntax with offset:

 <code class="language-sql">SELECT column1, column2,... FROM table_name LIMIT offset, number_of_rows;</code>

offset : Number of skipped lines (start position). number_of_rows : The number of rows returned from offset .

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How it works

The LIMIT clause controls the query results by specifying the number of records to be returned. The LIMIT clause is particularly useful for large database tables or for testing, analyzing or displaying interfaces only a small amount of data.

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Example

Suppose there is a product list called products :

productid	productname	price
1	laptop	1200
2	mouse	25
3	keyboard	45
4	Monitor	200
5	Tablet	300

Limit the number of rows returned

Query:

 <code class="language-sql">SELECT productname, price FROM products LIMIT 3;</code>

result:

productname	price
laptop	1200
mouse	25
keyboard	45

This query only returns the first three rows of the products table.

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Used in combination with OFFSET

To get the 4th row and the following three rows of data (paging scenario):

Query:

 <code class="language-sql">SELECT ProductName, Price FROM Products LIMIT 3 OFFSET 3;</code>

result:

productname	price
Monitor	200
Tablet	300

LIMIT 3 OFFSET 3 skips the first three lines and returns the next three lines.

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Common application scenarios of LIMIT

1. Pagination: LIMIT combined with OFFSET is often used for pagination of database results. For example, 10 records are displayed per page.
2. Testing and Development: Developers use LIMIT to view data samples, not entire datasets.
3. Performance optimization: When processing large tables, LIMIT can reduce data processing and transmission volume and improve query speed.

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Things to note

1. Sort: When there is no ORDER BY clause, the order in which LIMIT returns depends on the database engine.
2. Performance Impact: LIMIT can optimize performance, especially when processing large amounts of data.
3. Database compatibility: MySQL, PostgreSQL, SQLite and other databases all support LIMIT. SQL Server uses TOP, Oracle uses ROWNUM or FETCH FIRST.

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Summarize

The LIMIT clause is an effective tool to control the number of rows returned by query, and is widely used in paging, performance optimization and data processing. Whether used to build user interfaces, test data or analyze some results, LIMIT can efficiently manage data output.

Author: Abhay Singh Kathayat

Full-stack developer, proficient in front-end technology, and specializes in building efficient, scalable, user-friendly applications using a variety of programming languages ​​and frameworks. Contact email: kaashshorts28@gmail.com

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