Beginning SQL

Running the query, complete with a WHERE clause, produces the following final results:
State
Golden State
Mega State
New State
The GROUP BY clause isn’t limited to just one column; it can be two or more as the following query shows:
SELECT City, State
FROM MemberDetails
WHERE State IN (‘Mega State’, ‘Golden State’,’New State’)
GROUP BY City, State;
Executing the query produces the results in the following table:
City State
Big City Mega State
Dover Golden State
New Town New State
Orange Town New State
Townsville Mega State
Windy Village Golden State
The order of the columns in the GROUP BY clause affects the order of results, but it doesn’t change the
results as a whole, just the order in which they arrive.
Both examples include the same columns in the SELECT results set, as in the GROUP BY clause, and this is
no accident. Most DBMSs don’t allow the columns that appear in the results to differ from the columns
in the GROUP BY clause. The reason for this is that if you specify no group for a column in the SELECT
statement, then the DBMS has no way of deciding which value to include for a particular group.
Remember, your results can include only one identical record per group; each row represents the results
from a group of records and not the individual records themselves. You can’t include an ungrouped column;
otherwise there may be more than one row for each group, which isn’t allowed.
Summarizing and Aggregating Data
Grouping and Aggregating Data
Until now, results obtained from the database have all consisted of a set of individual records rather than
records that have been summarized by, say, including an average or counting records. Queries have
answered questions such as “Who are the members of the film club and which state do they live in?”
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