Interview Preparation
SQL Interview: Indexes, Transactions and ACID
The performance and concurrency half of a SQL interview: how indexes work, what they cost, ACID, isolation levels and deadlocks.
#Indexes
Structures that speed up data access.
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SQL
Query Optimisation and Pagination Performance
A practical checklist for making a slow query fast, and the specific fix for deep pagination that no amount of indexing solves.
SQL
When Indexes Help and When They Hurt
Indexes are not free. Learn the cases where the optimiser correctly ignores them, how to find unused and duplicate indexes, and how to maintain them.
SQL
Composite, Unique and Covering Indexes
Multi column indexes and why their order decides everything: the leftmost prefix rule, selectivity, covering indexes and index only scans.
SQL
What Indexes Are and Why They Exist
An index is a sorted lookup structure the database maintains for you. Learn how a B-tree finds a row, what an index costs, and the clustered index in...