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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 → Transactions 1

In MySQL a transaction spanning multiple DELETE statements rolls back correctly when
TRANSACTION is explicitly started with BEGIN/START TRANSACTION before the DELETEs
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DBMS → Deadlock 1

Deadlock scenario: T1 locks question_id=1 then tries to lock question_id=2; T2 locks question_id=2 then tries question_id=1. Resolution is
DBMS detects cycle, selects one transaction as victim (aborts it), other proceeds
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DBMS → Introduction to DBMS 36

Which query uses window function to find rank of each question by q_level within each assignment
SELECT assignment_id,id,q_level,RANK() OVER(PARTITION BY assignment_id ORDER BY q_level DESC) as rnk FROM questions
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To get next 5 questions after current question id=50 in same assignment_id=1
SELECT * FROM questions WHERE assignment_id=1 AND id>50 ORDER BY id LIMIT 5
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Which SQL creates an auto-updating updated_at column in MySQL
updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP
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Laravel $table->timestamps() creates exactly which columns
created_at TIMESTAMP NULL and updated_at TIMESTAMP NULL
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In the questions screenshot, q_level is NULL. This means
Questions have no difficulty level set
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To set q_level for all NULL questions in assignment 1 to level 2 in Laravel
DB::table('questions')->whereNull('q_level')->where('assignment_id',1)->update(['q_level'=>2])
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Which SQL verifies referential integrity of assignment_id in questions
SELECT q.* FROM questions q LEFT JOIN assignments a ON q.assignment_id=a.id WHERE a.id IS NULL
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MySQL auto_increment value can be reset with
ALTER TABLE questions AUTO_INCREMENT=1
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To copy questions from assignment 1 to assignment 2 (new rows) in SQL
INSERT INTO questions(question_type,q_level,question,option_a,option_b,option_c,option_d,option_e,right_answer_id,solution,is_deleted,created_at,updated_at) SELECT question_type,q_level,question,option_a,option_b,option_c,option_d,option_e,right_answer_id,solution,0,NOW(),NOW() FROM questions WHERE assignment_id=1 AND is_deleted=0
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DB::table('questions')->insert() vs DB::table('questions')->insertOrIgnore(): difference
insertOrIgnore skips rows that would violate UNIQUE constraints without throwing error
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DB::table('questions')->upsert(rows, uniqueBy, update) performs
INSERT rows; if unique key conflict UPDATE specified columns
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Codd's 12 rules define requirements for a fully relational DBMS. Rule 1 states
The information rule: all data stored in tables
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Entity integrity rule means
Primary key attributes must NOT have NULL values
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Referential integrity rule means
FKs must either be NULL or match PK values in referenced relation
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The degree (arity) of a relation is
Number of columns (attributes)
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The cardinality of a relation is
Number of rows (tuples) in the current instance
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Closed World Assumption in databases means
If data not recorded in DB, fact is assumed FALSE
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Three-valued logic in SQL uses values
TRUE, FALSE, and UNKNOWN (from NULL comparisons)
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NULL = NULL in SQL evaluates to
NULL/UNKNOWN
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Impedance mismatch problem arises from
OO programming model vs relational data model incompatibility
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Object-Relational Mapping (ORM) solves
Impedance mismatch by automatically mapping objects to database tables
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Which design pattern does Eloquent ORM use
Active Record: model = table, instance = row, CRUD methods on model
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Which is NOT a NoSQL database type
Relational table store
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MongoDB is an example of
Document store
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Redis is an example of
Key-value store (in-memory)
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Apache Cassandra is an example of
Wide-column (column-family) store
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Neo4j is an example of
Graph database
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BASE vs ACID: BASE stands for
Basically Available Soft-state Eventually consistent
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Which database property is BASE designed to relax compared to ACID
Strong Consistency for better availability and performance
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CAP theorem P stands for
Partition tolerance: system continues operating despite network partitions
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MongoDB vs MySQL: key structural difference
MongoDB: schema-less documents; MySQL: fixed-schema tables
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Which SQL command imports a SQL dump file in MySQL command line
mysql -u user -p database < dump.sql
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mysqldump command creates
A SQL dump file with CREATE TABLE and INSERT statements
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Which SQL shows all indexes on the questions table in MySQL
SHOW INDEX FROM questions
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CHECK TABLE questions in MySQL performs
Checks table for errors or corruption
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OPTIMIZE TABLE questions in MySQL
Defragments the table and updates statistics for better performance
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DBMS → Joins 1

Which relational algebra operation is equivalent to SQL NATURAL JOIN
πcommon(σA.k=B.k(A×B))
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DBMS → Relational Model 1

In relational model, a relation is formally defined as a SUBSET of the Cartesian product of
Its attribute domains (D1×D2×...×Dn)
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