What are grouping queries in SQL?

Grouping queries in SQL are used to aggregate data based on one or more columns.

Main operators and functions for grouping:

• GROUP BY: Divides rows into groups based on the values of specified columns.
• Aggregate functions: Perform calculations on groups of rows.
  • COUNT(): Counts the number of rows in a group.
  • SUM(): Sums the values in a column.
  • AVG(): Calculates the average value.
  • MIN(): Finds the minimum value.
  • MAX(): Finds the maximum value.
• HAVING: Filters groups after aggregation and applying GROUP BY, similar to WHERE for individual rows.

Example of using GROUP BY and the aggregate function COUNT():

SELECT column1, COUNT(*)  -- Selects the column for grouping and the number of rows in the group
FROM table_name
GROUP BY column1;  -- Groups by the values of column1

Example of using HAVING:

SELECT column1, COUNT(*)
FROM table_name
GROUP BY column1
HAVING COUNT(*) > 10;  -- Selects only groups where the number of rows is greater than 10

Comparison table of WHERE and HAVING:

Aspect	WHERE	HAVING
Purpose	Filters individual rows before GROUP BY	Filters groups of rows after GROUP BY
Applies to	Table columns	Results of aggregate functions
Order	Executed before GROUP BY	Executed after GROUP BY and aggregation