CS TECHIIE | SQL Notes and Solutions
Practical SQL exercise: Counts rows.
Objective
Counts rows.
Explanation
Read the statement clause by clause and predict the result before executing it. These examples use common relational SQL; table setup and exact syntax can vary between MySQL, PostgreSQL, SQL Server, Oracle and SQLite.
Safety check
Before running UPDATE or DELETE, run a SELECT with the same WHERE condition. Use a test database and a transaction for changes you need to verify.
Program / SQL Solution
SELECT COUNT(*) AS student_count FROM students;Practice and revision
- Run the example and verify the output.
- Change the input and test normal, boundary and invalid cases.
- Write the solution again without looking at the notes.
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