SQL Select Non-Unique Records

Introduction

SQL is a powerful language used for managing relational databases. One of the common tasks in SQL is to select records that are not unique. This can be done using the 'SELECT' statement along with the 'GROUP BY' clause.

Syntax

SELECT column1, column2, ... columnN
FROM table_name
GROUP BY column1, column2, ... columnN
HAVING COUNT(*) > 1;

The 'SELECT' statement is used to select the required columns from the table. The 'GROUP BY' clause is used to group the records based on one or more columns. The 'HAVING' clause is used to filter the non-unique records.

Code Sample

SELECT name, COUNT(*)
FROM employees
GROUP BY name
HAVING COUNT(*) > 1;

In this example, the 'employees' table has records with duplicate names. The query selects the 'name' column and counts the number of times each name appears in the table. The records are grouped by 'name' using the 'GROUP BY' clause. The 'HAVING' clause filters the records with a count greater than 1, which are the non-unique records.

Conclusion

Selecting non-unique records in SQL is a common task and can be achieved using the above syntax. It is important to use the 'GROUP BY' and 'HAVING' clauses correctly to get accurate results.