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SQLBeginner#fundamentals
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SQL Interview Questions
50 questions · Queries, joins, indexes, transactions and database design interview questions.
50 results
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SQLBeginner#fundamentals
What is the difference between DBMS and RDBMS?
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SQLBeginner#ddl#dml
Difference between DELETE, TRUNCATE and DROP?
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SQLIntermediate#joins
Explain all types of JOIN with an example.
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SQLIntermediate#joins
What is a SELF JOIN?
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SQLIntermediate#aggregates
Difference between WHERE and HAVING?
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SQLIntermediate#queries
What is the logical order of execution of a SELECT query?
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SQLBeginner#keys
Primary key vs unique key vs foreign key?
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SQLBeginner#keys
What is a composite key?
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SQLIntermediate#keys
What is a candidate key and a super key?
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SQLIntermediate#normalization
What is normalization? Explain 1NF, 2NF and 3NF.
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SQLAdvanced#normalization
What is BCNF?
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SQLIntermediate#normalization
What is denormalization and when do you use it?
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SQLBeginner#sets
UNION vs UNION ALL?
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SQLIntermediate#sets
What are INTERSECT and EXCEPT/MINUS?
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SQLIntermediate#indexes#performance
What is an index? What are the trade-offs?
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SQLAdvanced#indexes
Clustered vs non-clustered index?
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SQLAdvanced#indexes#performance
What is a covering index?
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SQLAdvanced#indexes#performance
Why might an index not be used by a query?
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SQLIntermediate#subqueries
What is a subquery? Correlated vs non-correlated?
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SQLIntermediate#subqueries
Difference between IN, EXISTS and JOIN?
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SQLIntermediate#queries#cte
What is a CTE (Common Table Expression)?
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SQLAdvanced#cte
How do you write a recursive CTE?
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SQLIntermediate#views
What is a view? What is a materialized view?
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SQLIntermediate#transactions
Explain the ACID properties.
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SQLAdvanced#transactions
What are transaction isolation levels?
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SQLAdvanced#transactions
What is a deadlock and how do you avoid it?
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SQLAdvanced#transactions#concurrency
What are optimistic and pessimistic locking?
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SQLIntermediate#procedures
What is a stored procedure and how does it differ from a function?
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SQLIntermediate#triggers
What is a trigger?
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SQLBeginner#aggregates#nulls
What are aggregate functions and how do NULLs affect them?
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SQLBeginner#nulls
How do you handle NULL values in SQL?
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SQLBeginner#functions
What is the difference between COALESCE and CASE?
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SQLAdvanced#windows
What is a window function?
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SQLAdvanced#windows
Difference between ROW_NUMBER, RANK and DENSE_RANK?
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SQLAdvanced#windows
What do LAG and LEAD do?
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SQLIntermediate#queries#windows
How do you find the Nth highest salary?
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SQLIntermediate#queries
How do you find and delete duplicate rows?
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SQLIntermediate#queries
How do you find employees earning more than their department average?
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SQLIntermediate#joins#queries
How do you find records in table A that are missing in table B?
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SQLBeginner#datatypes
CHAR vs VARCHAR vs TEXT?
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SQLAdvanced#performance
What is the difference between an execution plan and EXPLAIN ANALYZE?
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SQLAdvanced#performance
How do you optimise a slow SQL query?
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SQLAdvanced#scaling
What is partitioning and how does it differ from sharding?
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SQLIntermediate#architecture
OLTP vs OLAP?
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SQLIntermediate#security
What is SQL injection and how do you prevent it?
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SQLAdvanced#aggregates
What is GROUP BY with ROLLUP?
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SQLIntermediate#queries#performance
How do you paginate results efficiently?
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SQLBeginner#fundamentals
What are DDL, DML, DQL, DCL and TCL?
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SQLIntermediate#joins