Quick Revision

GK One-Line Question & Answer

15541+ short questions with short answers, covering every category and sub-category on the site — no long articles to scroll through. Good for a fast recap before an exam, or a few minutes of daily practice.

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DBMS → SQL Basics 5

HAVING clause filters
Groups AFTER GROUP BY aggregation
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ORDER BY clause
Sorts result set in ASC (default) or DESC order
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GROUP BY groups rows that
Share same values in specified columns
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LAG(salary,1) OVER(ORDER BY date) returns
Previous row salary value in ordered partition
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LEAD(salary,1) OVER(ORDER BY date) returns
Next row salary value in ordered partition
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DBMS → Introduction to DBMS 26

SELECT DISTINCT removes
Duplicate rows from result set
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COUNT(*) counts
ALL rows including those with NULLs
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EXISTS subquery returns TRUE when
Subquery returns at least one row
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UNION combines results and by default
Removes duplicate rows
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UNION ALL keeps
ALL rows including duplicates
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MAX() returns
Highest value
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SUM() returns
Total sum of numeric values
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AVG() returns
Average (arithmetic mean) of values
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A scalar subquery returns
Exactly one row and one column (single value)
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WITH clause (CTE) creates
Named temporary result set valid within one SQL statement
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ROW_NUMBER() assigns
Unique sequential integer to each row
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RANK() gives 1,2,2,4 for ties because
Skips rank numbers AFTER ties (gap after tied ranks)
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DENSE_RANK() gives 1,2,2,3 for ties because
It never skips rank numbers after ties
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GRANT command gives
Specific privileges to a user on a database object
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REVOKE command
Removes privileges
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SAVEPOINT creates
Named marker within transaction for partial rollback
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UNIQUE constraint prevents
Duplicate non-NULL values in a column
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CHECK constraint ensures
Column values satisfy a boolean expression
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ON DELETE CASCADE
Automatically deletes child rows when parent row deleted
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COALESCE(NULL,NULL,5,10) returns
5
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NULLIF(5,5) returns
NULL
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% in SQL LIKE matches
Zero or more characters
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BETWEEN a AND b is
Inclusive on both ends (a ≤ value ≤ b)
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WHERE col IN (1,2,3) equals
col=1 OR col=2 OR col=3
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CASE expression provides
Conditional IF-THEN-ELSE logic within SQL query
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X→Y (X functionally determines Y) means
For each X value there is exactly one corresponding Y value
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DBMS → Joins 3

INNER JOIN returns
Only rows where join condition satisfied in BOTH tables
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LEFT JOIN returns
All left table rows plus matching right rows (NULLs for no match)
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FULL OUTER JOIN returns
All rows from both; NULLs for non-matches
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DBMS → Views 1

A view in SQL is
Virtual table defined by a SELECT query
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DBMS → PL/SQL 1

A trigger automatically executes when
Specified DML event occurs on a table
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DBMS → Transactions 2

COMMIT permanently
Saves all transaction changes to database
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ROLLBACK
Undoes changes since last COMMIT or SAVEPOINT
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DBMS → Normalization 2

Normalization is which database design approach?
Bottom-up
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1NF requires
All attributes atomic and no repeating groups
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