Data Engineering Associate with Databricks Practice Exam

Which SQL statement is used to deduplicate rows in a table?

1. SELECT DISTINCT

2. DELETE

3. CREATE VIEW

4. GROUP BY

The correct answer is: SELECT DISTINCT

The use of the SQL statement SELECT DISTINCT is effective for deduplicating rows in a table because it retrieves unique records from the result set. When this statement is executed, it scans the specified columns and filters out any duplicate entries, returning only one instance of each unique row based on the selected fields. This is particularly useful when you want to have a clean dataset for analysis or reporting, where duplicates could skew results or provide incorrect interpretations. For instance, if you have a table with multiple entries for the same customer, using SELECT DISTINCT on the customer column would yield a single entry for each customer, thereby facilitating a clearer understanding of customer counts and demographics. Other SQL statements like DELETE are used to remove specific rows from a table but do not inherently identify duplicates across multiple records. The CREATE VIEW statement is intended for creating a virtual table based on the results of a query but does not serve the purpose of deduplication on its own. Finally, GROUP BY is often used in conjunction with aggregate functions to group data but does not directly deduplicate the rows; rather, it creates a summary based on grouped criteria. SELECT DISTINCT directly addresses the need to avoid duplicate entries in query results.