Interview Q&A / SQL & DBMS
SQL & DBMS interview questions
Joins, keys, normalisation, indexes and transactions for placement and backend interviews.
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- What is a deadlock in a database and how is it handled?
A deadlock happens when two transactions each hold a lock the other needs, so neither can proceed. The database detects the cycle and aborts one transaction as the victim, and the application should retry it.
IntermediateQuick answer1 min read - What is the difference between optimistic and pessimistic locking?
Pessimistic locking locks the row up front so others must wait, assuming conflicts are likely. Optimistic locking takes no lock and checks at update time, usually with a version number, whether someone else changed the row.
IntermediateQuick answer1 min read