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 the difference between a clustered and a non-clustered index?
A clustered index decides the physical order in which table rows are stored, so the table itself is the index and there can be only one. A non-clustered index is a separate structure holding the indexed values plus a pointer back to the row, and a table can have many.
AdvancedIn-depth4 min read - What is the default window frame, and why can LAST_VALUE give a surprising answer?
With ORDER BY, the default frame runs from the first row to the current row, so LAST_VALUE returns the current row's value. To get the true last value, extend the frame with ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING.
AdvancedQuick answer1 min read