When it comes to loading data into Oracle databases, SQL Loader is a popular tool that offers high-performance data loading capabilities. While traditional SQL Loader functionality is powerful on its own, it also provides advanced features, such as working with external tables and utilizing preprocessor executables. In this blog post, we will explore how to leverage these features to enhance the data loading process in SQL Loader.

What are External Tables?

External tables are a feature in Oracle databases that allow you to treat external data files as virtual tables within the database. These tables provide a convenient and efficient way to access and manipulate data stored outside of the database structure. External tables offer several benefits, including improved loading performance, reduced storage requirements, and simplified data integration.

To create an external table in SQL Loader, you need to define its structure using the CREATE TABLE ... ORGANIZATION EXTERNAL statement. This statement specifies the table’s column definitions, access parameters, and the location of the external data file.

Leveraging Preprocessor Executables

SQL Loader also supports preprocessor executables, which allow you to transform or preprocess data files before they are loaded into the database. This feature is useful when you need to perform data cleansing, filtering, or any other data manipulation operation prior to loading the data.

To use a preprocessor executable with SQL Loader, you can specify it using the PREPROCESSOR keyword in the control file. The preprocessor executable receives the data file as input, applies the necessary transformations, and outputs the modified file. SQL Loader then loads the transformed data into the database.

Example: Loading Data from CSV File Using External Table and Preprocessor Executable

Let’s walk through an example to illustrate how to utilize external tables and preprocessor executables in SQL Loader to load data from a CSV file.

1. Create an external table definition:

CREATE TABLE ext_emp (
  emp_id NUMBER,
  emp_name VARCHAR2(50),
  emp_salary NUMBER
)
ORGANIZATION EXTERNAL (
  TYPE ORACLE_LOADER
  DEFAULT DIRECTORY ext_data_dir
  ACCESS PARAMETERS (
    RECORDS DELIMITED BY NEWLINE
    NOBADFILE
    NOLOGFILE
    FIELDS TERMINATED BY ','
    (
      emp_id,
      emp_name,
      emp_salary
    )
  )
  LOCATION ('employees.csv')
)
REJECT LIMIT UNLIMITED;

In this example, we create an external table named ext_emp with three columns: emp_id, emp_name, and emp_salary. The external table is defined to use the Oracle Loader access driver and is located in the ext_data_dir directory. The data file, employees.csv, is assumed to be present in the same directory.

1. Create a preprocessor executable script (e.g., preprocess.sh) to modify the data file as needed:

#!/bin/bash
sed -i 's/\"//g' $1

In this simple example, the preprocessor script removes double quotes from the data file using the sed command.

1. Create a control file (load_data.ctl) to configure SQL Loader:

LOAD DATA
INFILE 'ext_emp'
APPEND
INTO TABLE emp
FIELDS TERMINATED BY ","
TRAILING NULLCOLS
(
  emp_id,
  emp_name,
  emp_salary
)

The control file specifies where to load the data (INTO TABLE emp) and the column mappings. It assumes that the external table definition, ext_emp, is already created.

1. Run SQL Loader with the control file, specifying the preprocessor executable:

sqlldr control=load_data.ctl PREPROCESSOR='preprocess.sh'

This command executes SQL Loader and applies the preprocessor script on the data file before loading it into the emp table.

By leveraging external tables and preprocessor executables, you can enhance the data loading process in SQL Loader by directly accessing external data files and performing transformations on the data. This enables you to efficiently load data into Oracle databases while maintaining data integrity and consistency.

Conclusion

In this blog post, we explored how to work with external tables and preprocessor executables in SQL Loader. We discussed the benefits of using external tables and demonstrated how to create and utilize them for loading data from external files. Additionally, we covered the concept of preprocessor executables and showed how to incorporate them into the data loading process. By leveraging these features, you can achieve a more efficient and streamlined data loading experience with SQL Loader.

#SQLLoader #OracleDatabase