If you want to change the query of a view named employee_details to include only employees from the 'HR' department, which SQL command will produce the correct output?
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SQL - Views
If you want to change the query of a view named employee_details to include only employees from the 'HR' department, which SQL command will produce the correct output?
ADROP VIEW employee_details; CREATE VIEW employee_details AS SELECT * FROM employees WHERE department = 'HR';
BMODIFY VIEW employee_details AS SELECT * FROM employees WHERE department = 'HR';
CUPDATE VIEW employee_details SET query = 'SELECT * FROM employees WHERE department = ''HR''';
DALTER VIEW employee_details AS SELECT * FROM employees WHERE department = 'HR';
Step-by-Step Solution
Solution:
Step 1: Check ALTER VIEW support
Not all SQL systems support ALTER VIEW to redefine a view; often DROP and CREATE is used.
Step 2: Analyze options
DROP VIEW employee_details; CREATE VIEW employee_details AS SELECT * FROM employees WHERE department = 'HR'; drops the old view and creates a new one with the desired query, which works universally. ALTER VIEW employee_details AS SELECT * FROM employees WHERE department = 'HR'; may fail if ALTER VIEW is unsupported. Options B and C use invalid syntax.
Final Answer:
DROP VIEW employee_details; CREATE VIEW employee_details AS SELECT * FROM employees WHERE department = 'HR'; -> Option A
Quick Check:
Drop and recreate view to change query = D [OK]
Quick Trick:Drop and recreate view if ALTER VIEW is unsupported [OK]
Common Mistakes:
MISTAKES
Assuming ALTER VIEW always works
Using UPDATE or MODIFY VIEW which are invalid
Not recreating view after drop
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