What is layout validation in SQL ETL testing?

Layout validation in SQL ETL testing refers to the process of verifying the structure and format of the data during the Extract, Transform, Load (ETL) process. This validation ensures that the data being moved from source systems to target systems conforms to the expected layout or schema.

Here are key aspects of layout validation in SQL ETL testing:

1. Schema Consistency:

   • Ensure that the data extracted from source systems adheres to the expected schema or structure. This includes checking the consistency of column names, data types, and relationships.

2. Field Mapping:

   • Validate that the mapping of fields (columns) between source and target systems is accurate. Confirm that each field from the source system aligns with its corresponding field in the target system.

3. Data Types and Lengths:

   • Verify that data types and lengths of columns in the target system match the specifications defined during the ETL design. This ensures that there are no data type mismatches or truncation issues.

4. Nullability Constraints:

   • Check whether columns that are expected to allow NULL values in the source system are correctly mapped to columns with appropriate nullability constraints in the target system.

5. Default Values:

   • Validate that default values, if defined for any columns, are correctly applied during the transformation process.

6. Key Constraints:

   • Confirm that primary key and foreign key constraints are maintained as data is loaded into the target system. Ensure that relationships between tables are preserved.

7. Unique Constraints:

   • Ensure that columns marked as unique in the source system are correctly handled to maintain uniqueness in the target system.

8. Sequence and Order:

   • Verify that the sequence and order of data in the target system match the expectations. This is especially important when the order of records matters for reporting or downstream processes.

9. Metadata Validation:

   • Validate metadata associated with the layout, such as data dictionaries or metadata repositories. Ensure that documentation accurately reflects the expected layout and transformations.

10. Data Integrity Checks:

    • Perform checks to identify data integrity issues, such as missing or duplicate records, and address these issues during the ETL process.

11. Handling of Special Characters:

    • Verify that the ETL process handles special characters or encoding requirements appropriately, especially if the source and target systems have different character sets.

Layout validation is a critical aspect of ETL testing as it helps ensure that the transformed data maintains its structural integrity and aligns with the expectations set during the ETL design phase. This type of testing is typically performed using SQL queries to compare the structure and content of source and target tables, along with any necessary data transformation logic.