SQL GROUP BY.
The GROUP BY Clause
- The GROUP BY clause is intimately connected to aggregates.
- The clause divides a table into a sets of rows, and aggregate functions produce summary values for each set-group.
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These values are called vector aggregates.
GROUP BY syntax included in the SELECT statement:
SELECT select_list FROM table/view_list [WHERE search_conditions] [GROUP BY group_by_list] [ORDER BY order_by_list ]
- Just as you can sort multiple items, you can form groups within groups.
- You separate the grouping elements with commas, and go from large groups to progressively smaller ones.
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GROUP BY parts tables in a set of rows, but not
necessarily sort them in an orderly sequence.
Here is an example of using one item in the GROUP BY clause:MySQL, Oracle, SQL server, PostgreSQL:
select publisher, min(price) "Low Price", max(price) as "High price", count(*) "Numbers" from bookstore group by publisher order by publisher, count(*);
The result should be:publisher Low Price High price Numbers Addison Wesley 39 39 1 Apress 1 OReilly 32 32 1 Sams Publishing 49 49 1 Wrox 29 42 5
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