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SQLite DISTINCT Clause

The DISTINCT clause is used in SQL queries to return only distinct (unique) values from a table or result set. This can be handy when analyzing data and trying to remove duplicate entries.

Syntax

The basic syntax for using the DISTINCT clause in a SQLite query is as follows:

SELECT DISTINCT column1, column2, ...
FROM table_name
WHERE condition;

In the above syntax, column1, column2, etc. refer to the columns that you want to retrieve unique values for. The FROM clause specifies the name of the table to retrieve data from, while the WHERE clause is optional and is used to filter the data based on certain conditions.

Example

Suppose we have a table called employees and we want to retrieve the unique last names of all employees in the table. We can use the DISTINCT clause in our SELECT statement to remove duplicate last names.

SELECT DISTINCT last_name
FROM employees;

Output

The output of the above query would be a list of distinct last names in the employees table:

Smith
Johnson
Lee
Brown

Explanation

In the above example, the SELECT statement selects the last_name column from the employees table and uses the DISTINCT keyword to retrieve only unique values. The resulting output is a list of distinct last names from the employees table.

Use

The DISTINCT clause is useful in queries where you need to remove duplicate entries from a result set. It is commonly used for data analysis to get a better understanding of the unique values in a dataset.

Important Points

  • The DISTINCT clause works only on the selected columns in the SELECT statement.
  • The DISTINCT clause can be used in combination with ORDER BY, GROUP BY, LIMIT, and other clauses to refine the results of a SELECT statement.
  • The performance of DISTINCT can be slow for large datasets, as it needs to compare each row with all the previous rows to make sure that no duplicates are returned.

Summary

In this tutorial, we learned about the SQLite DISTINCT clause, which is used to return only distinct values from a table or result set. We saw examples of how to use the DISTINCT clause in a SELECT statement to remove duplicate entries and retrieve unique values from a table. DISTINCT is a powerful tool for refining the results of SQL queries and is commonly used for data analysis to retrieve unique values in a dataset.

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