Duplicates are a common issue that database administrators often encounter during data loading or bulk data insertion operations. It is crucial to handle duplicates effectively to ensure the integrity and accuracy of the database. In this blog post, we will explore how to handle duplicate records during loading using SQL Loader.

Table of Contents

• Introduction to SQL Loader
• Identifying Duplicate Records
• Strategies to Handle Duplicates
• Example: Handling Duplicates with SQL Loader
• Conclusion

Introduction to SQL Loader

SQL Loader is a command-line tool provided by Oracle to load data from external files into Oracle database tables. It offers various features to efficiently load massive amounts of data quickly. However, by default, SQL Loader does not handle duplicate records automatically, and it depends on the database configuration to enforce uniqueness.

Identifying Duplicate Records

Before we proceed with handling duplicate records, it is essential to identify them accurately. The duplicate records can be identified by one or more columns or a combination of columns that define uniqueness in a table. Typically, a primary key or a unique key constraint is used to enforce uniqueness in a table.

Strategies to Handle Duplicates

Here are a few strategies to handle duplicate records during loading using SQL Loader:

1. Inserting Only Unique Records

One approach is to insert only the unique records and discard the duplicate ones. This can be achieved by enabling the UNIQUE option in the SQL Loader control file. SQL Loader will skip the duplicate records during the loading process.

2. Skipping Duplicate Records

Another strategy is to skip the duplicate records altogether without performing any insert operation. Using the SKIP option in the SQL Loader control file, duplicate records can be ignored during the loading process.

3. Handling Duplicate Records with Custom Logic

In some cases, you may want to handle duplicate records using custom logic. You can achieve this by using the WHEN clause in the SQL Loader control file. By specifying a condition, you can choose to insert/update/delete records based on your specific requirements.

Example: Handling Duplicates with SQL Loader

Let’s consider an example where we have a customers table with a unique constraint on the email column. We want to load a file containing customer data into the table while handling duplicate email records:

LOAD DATA 
INFILE 'customer_data.csv'
INTO TABLE customers
FIELDS TERMINATED BY ',' 
(
  name,
  email
)
WHEN NOT MATCHED THEN 
  INSERT (name, email)
  VALUES (:name, :email)

In this example, the WHEN NOT MATCHED clause ensures that only unique email records are inserted into the customers table, and duplicate email records are skipped during the loading process.

Conclusion

Handling duplicate records during loading is crucial to maintain data integrity in the database. SQL Loader provides several strategies to handle duplicates effectively. By choosing the appropriate approach based on your requirements, you can ensure that only unique records are inserted and duplicates are handled correctly.