When dealing with large datasets, loading data into tables can be a complex task. One challenge is to ensure that the data being loaded adheres to unique constraints defined on the tables. In this blog post, we will explore how to use SQL Loader to efficiently load data while enforcing unique constraints.

What is SQL Loader?

SQL Loader is a powerful Oracle utility that enables high-speed data loading into Oracle databases from flat files. It provides a flexible and efficient way to load large quantities of data by leveraging direct path loading and parallel processing.

Unique Constraints

Unique constraints in a database table ensure that a column or a combination of columns have unique values. These constraints prevent duplicate or conflicting data from being inserted into the table. When loading data into tables with unique constraints, it is crucial to handle any potential duplicates or violations of the constraint.

Using SQL Loader to Handle Unique Constraints

SQL Loader provides several ways to handle unique constraints during data loading:

1. SKIP and CONTINUEIF

The SKIP and CONTINUEIF clauses in the SQL Loader control file can be used to skip or continue loading records depending on specific conditions. By specifying a condition that checks for a duplicate value in a column, you can choose to skip those records or continue loading them without violating the unique constraint.

LOAD DATA
INFILE 'datafile.csv'
BADFILE 'badfile.bad'
DISCARDFILE 'discardfile.dsc'
APPEND INTO TABLE my_table
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
( column1, column2, column3
  )
CONTINUEIF column1 = CONCATENATED

In the above example, the CONTINUEIF clause checks if the value in column1 already exists in the table. If it does, the record will be continued to be loaded.

2. CONCATENATE

The CONCATENATE clause in the SQL Loader control file allows combining multiple columns to create a unique value. This can be useful when unique constraints involve multiple columns in the table.

LOAD DATA
INFILE 'datafile.csv'
BADFILE 'badfile.bad'
DISCARDFILE 'discardfile.dsc'
APPEND INTO TABLE my_table
FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"'
( column1, column2, column3  
  )
CONCATENATE column1, column2 INTO concatenated

In the above example, the column column1 and column2 are combined into a new column concatenated. The CONCATENATE clause ensures the uniqueness of the combined values, avoiding violations of the unique constraint.

3. Database Triggers

If the above methods are not suitable for your case, you can consider using database triggers to validate the uniqueness of data after the load. You can create a trigger that runs after each insert operation and checks the uniqueness of the inserted data. If duplicates are found, the trigger can roll back the transaction or handle the exception as needed.

CREATE OR REPLACE TRIGGER check_unique AFTER INSERT ON my_table
FOR EACH ROW
DECLARE
  duplicate_count NUMBER;
BEGIN
  SELECT COUNT(*)
  INTO duplicate_count
  FROM my_table
  WHERE column1 = :NEW.column1
    AND column2 = :NEW.column2;
    
  IF duplicate_count > 1 THEN
    RAISE_APPLICATION_ERROR(-20001, 'Duplicate data found');
  END IF;
END;

In the above example, we create an AFTER INSERT trigger that checks for duplicates based on the columns column1 and column2. If duplicates are found, an error is raised, indicating a violation of the unique constraint.

Conclusion

Loading data into tables with unique constraints using SQL Loader is an essential task in data management. By leveraging the capabilities of SQL Loader, such as the SKIP and CONTINUEIF clauses or combining columns using CONCATENATE, you can efficiently handle unique constraints during the data loading process. If these methods are not suitable, you can resort to using database triggers to validate the uniqueness after the load. Understanding how to handle unique constraints in SQL Loader is crucial for ensuring data integrity.

#sqlloader #uniqueconstraints