Grouping Records
SOQL provides the GROUP BY syntax for grouping records by one or more fields. When a query contains a grouping, its results are collapsed into a single record for each unique value in the grouped field. Because you can no longer return individual field values, all fields not specified as grouped must be placed within aggregate functions.
Listing 5.3 shows a simple example of grouping records without aggregate functions. It examines all the records in the Contact object and returns only the unique values of the field Region__c.
Listing 5.3 Returning Unique Records by Grouping Them
for (AggregateResult r : [ SELECT Region__c FROM Contact GROUP BY Region__c ]) { System.debug(r.get('Region__c')); ...
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