Quick Revision

GK One-Line Question & Answer

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Computer Fundamentals → Introduction to Computer 39

SQL ORDER BY default sort order is?
Ascending
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Which SQL keyword filters duplicate rows?
DISTINCT
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SQL LIKE operator uses which wildcard for multiple characters?
%
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SQL BETWEEN operator is?
Inclusive of both boundary values
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NULL in SQL represents?
Unknown or missing value
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IS NULL vs = NULL in SQL?
IS NULL is correct; = NULL always returns false (no value equals NULL)
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TRUNCATE vs DELETE in SQL?
TRUNCATE faster (removes all rows, can't rollback in many DBs); DELETE is slower but rollbackable
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DROP TABLE vs TRUNCATE TABLE?
DROP removes table structure AND data; TRUNCATE removes only data
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Which SQL clause groups rows with same values?
GROUP BY
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HAVING clause in SQL filters?
Groups created by GROUP BY after aggregation
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Which aggregate function calculates average?
AVG()
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SQL subquery is?
A nested SQL query inside another query
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Correlated subquery refers to?
A subquery that references a column from the outer query
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EXISTS operator in SQL?
Returns TRUE if subquery returns any rows
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UNION vs UNION ALL in SQL?
UNION removes duplicates; UNION ALL keeps all rows including duplicates
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EXCEPT (or MINUS in Oracle) returns?
Rows in first query not present in second query
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INTERSECT in SQL returns?
Rows common to both queries
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Which SQL function gets current date and time?
All of the above (varies by DBMS)
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CHAR vs VARCHAR in SQL?
CHAR is fixed-length; VARCHAR is variable-length (more efficient for varying text)
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Which SQL data type stores large text?
TEXT / CLOB (Character Large Object)
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BLOB in SQL stores?
Binary Large Objects — images, files, audio
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AUTO_INCREMENT in MySQL?
Automatically generates unique sequential integers for primary key
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Which MySQL command shows all databases?
SHOW DATABASES
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USE database_name in MySQL?
Selects/switches to specified database for subsequent queries
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DESCRIBE table_name in MySQL?
Shows table structure (column names, types, constraints)
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EXPLAIN in SQL is used for?
Showing query execution plan for performance analysis
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Which MySQL statement modifies table structure?
ALTER TABLE
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Which constraint ensures unique values in a column?
UNIQUE
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CHECK constraint in SQL?
Validates that column values meet specified condition
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DEFAULT constraint in SQL?
Specifies a default value when no value is provided during INSERT
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Stored procedure advantages include?
Pre-compiled execution, reduced network traffic, code reuse, security
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Function vs Stored Procedure in SQL?
Functions must return a value and can be used in SELECT; procedures can't be in SELECT
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Trigger AFTER INSERT fires?
After a row is successfully inserted into the table
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BEFORE DELETE trigger is used to?
Perform actions before a row is deleted (e.g., archive data)
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Which SQL view cannot be updated?
View with GROUP BY, DISTINCT, aggregates, or multiple tables (in most cases)
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Database cursor is used for?
Row-by-row processing of query results
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COMMIT in SQL?
Permanently saves all changes made in the current transaction
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ROLLBACK in SQL?
Undoes all changes made since the last COMMIT or SAVEPOINT
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SAVEPOINT in SQL allows?
Partial rollback to a named point within a transaction
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Computer Fundamentals → Memory Units 1

Materialized view differs from regular view because?
Stores the query result physically — must be refreshed to stay current
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