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Answer: Aggregate Records Using COUNT

Explore how to use the SQL COUNT aggregate function to count records based on conditions, including filtering for NULL values. Understand the use of aliases, WHERE clauses, and alternate approaches like CASE and IF statements. This lesson helps you write precise queries to summarize and analyze data efficiently.

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Solution

The solution is given below:

MySQL
/* The query to find the count of exams missed */
SELECT COUNT(*) AS AbsentStudents
FROM   StudentGrades
WHERE  Marks IS NULL;

Explanation

The explanation of the solution code is given below:

  • Line 2: The SELECT query uses the COUNT(*) function to count the number of rows in the table. We use AS to set an alias for the column.

  • Line 3: The FROM clause specifies the table, StudentGrades.

  • Line 4: In the WHERE clause, we specified the condition to filter the data. The IS NULL keyword is used specifically to check if the value is NULL.

Recall of relevant concepts

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