SQL COUNT

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The COUNT() function is an aggregate function used to count the number of rows or values in a table.
👉 In simple words:
COUNT() returns the total number of records that match a condition.

Important Points
1. COUNT(*) → counts all rows
2. COUNT(column) → counts non-NULL values
3. COUNT(DISTINCT column) → counts unique values
4. Often used with GROUP BY for reports

Basic Syntax 

SELECT COUNT(column_name)
FROM table_name;

Explanation

COUNT(column_name) → Counts non-NULL values in a column
COUNT(*) → Counts all rows in the table

COUNT All Rows 

SELECT COUNT(*)
FROM Students;

This counts all rows, including rows with NULL values.

COUNT Specific Column

SELECT COUNT(Age)
FROM Students;

COUNT(column) does not count NULL values

COUNT with WHERE 

SELECT COUNT(*)
FROM Students
WHERE Class = 10;

COUNT with GROUP BY

SELECT Class, COUNT(*) AS TotalStudents
FROM Students
GROUP BY Class;

COUNT with DISTINCT

SELECT COUNT(DISTINCT Class)
FROM Students;


Simple Definition (Exam/Interview):
COUNT() is an SQL aggregate function used to count the number of rows or non-NULL values in a table or column.

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