RDSolutions Interview Questions, Process, and Tips

SQL joins combine rows from two or more tables based on related columns, enabling complex queries and data analysis.

• INNER JOIN: Returns records with matching values in both tables. Example: SELECT * FROM A INNER JOIN B ON A.id = B.id;

• LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table and matched records from the right table. Example: SELECT * FROM A LEFT JOIN B ON A.id = B.id;

• RIGHT JOIN (or RIGHT O...read more

A stored procedure is a precompiled collection of SQL statements stored in a database for reuse and efficiency.

• Encapsulates complex SQL logic for reuse, e.g., calculating total sales.

• Improves performance by reducing network traffic, e.g., executing multiple queries in one call.

• Enhances security by controlling access to data, e.g., granting execute permissions only.

• Supports parameters for dynamic execution, e.g., passin...read more

UNION combines results from two queries, removing duplicates; UNION ALL includes all results, retaining duplicates.

• UNION removes duplicate rows from the result set.

• UNION ALL includes all rows, even duplicates.

• Example of UNION: SELECT column1 FROM table1 UNION SELECT column1 FROM table2;

• Example of UNION ALL: SELECT column1 FROM table1 UNION ALL SELECT column1 FROM table2;

• UNION may be slower due to duplicate removal, whi

Identifying duplicate data involves using SQL queries or data profiling techniques to find repeated entries in a dataset.

• Use SQL queries with GROUP BY and HAVING clauses to find duplicates. Example: SELECT column_name, COUNT(*) FROM table_name GROUP BY column_name HAVING COUNT(*) > 1.

• Utilize data profiling tools that can automatically detect duplicates based on defined criteria.

• Implement data validation rules during...read more