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SQL or Structured Query Language is a universal language for managing and processing data stored in Relational Database Management System (RDBMS) or for stream processing in a Relational Data Stream Management System (RDSMS). Among the many clauses in SQL, a conceptually fundamental one is the GROUP BY clause.
Understanding SQL GROUP BY Clause
The GROUP BY clause is used in collaboration with the SELECT statement to arrange identical data into groups. This statement is often used with aggregate functions like COUNT, MAX, MIN, SUM, AVG to group the result-set by one or more columns.
For instance, consider a ‘Sales’ table with the following data representation:
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Salesperson Sales John 10000 Paul 20000 Mike 5000 John 12000 Paul 18000 Mike 7000 |
And if we would like to find the total sales by each salesperson, we could use the GROUP BY clause as follows:
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SELECT salesperson, SUM(sales) as total_sales FROM sales GROUP BY salesperson; |
The Output would be
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Salesperson Total_Sales John 22000 Paul 38000 Mike 12000 |
How Does SQL GROUP BY clause Work?
The SQL GROUP BY statement works by aggregating the results on the basis of the fields specified in the GROUP BY clause. It organizes the result set into groups and works on the selectable fields. In the above example, the identical ‘salesperson’ records are grouped, and the corresponding ‘sales’ values are aggregated (since we’re using SUM as the aggregation function).
In Conclusion
The GROUP BY clause is a powerful feature in SQL, essential in carrying out operations that require grouping of identical data in some way. It reduces the redundancies in reporting and allows for more complex calculations across groups. Its widespread use in conjunction with aggregate functions lends it undeniable importance in the SQL querying process.