SQL Data Analyst Interview Questions and Answers

Query optimization involves using indexes, reducing unnecessary joins, and minimizing data retrieval.

• Use indexes on columns frequently used in WHERE clauses

• Avoid using SELECT * and only retrieve necessary columns

• Minimize the use of functions in WHERE clauses

• Reduce unnecessary joins by using INNER JOIN instead of OUTER JOIN

• Use EXISTS instead of IN for subqueries

Types of constraints in SQL include primary key, foreign key, unique, check, and not null constraints.

• Primary key constraint ensures each row in a table is uniquely identified.

• Foreign key constraint enforces referential integrity between two tables.

• Unique constraint ensures that all values in a column are unique.

• Check constraint restricts the values that can be inserted into a column.

• Not null constraint ensures a column cannot have a null value.