Aggregations Reference

Aggregations allow you to determine further information about the overall result in addition to the actual search results. These include totals, unique values, or the average of a field.

The DAL knows two types of aggregations:

• metric aggregation - This type of aggregation applies a mathematical formula to a field. A metric aggregation always has a calculated result. These are aggregations to calculate sums or maximum values.
• bucket aggregation - With this type of aggregation, a list of keys is determined. Further aggregations can then be determined for each key.

Name	Type	Description
avg	metric	Average of all numeric values for the specified field
count	metric	Number of records for the specified field
max	metric	Maximum value for the specified field
min	metric	Minimal value for the specified field
stats	metric	Stats overall numeric values for the specified field
sum	metric	Sum of all numeric values for the specified field
entity	bucket	Groups the result for each value of the provided field and fetches the entities for this field
filter	bucket	Allows to filter the aggregation result
terms	bucket	Groups the result for each value of the provided field and fetches the count of affected documents
histogram	bucket	Groups the result for each value of the provided field and fetches the count of affected documents. Although allows to provide date interval (day, month, ...)
range	bucket	Groups the result for each defined set of ranges into each bucket - bucket of numerical data and a count of items/documents for each bucket

Avg aggregation

The Avg aggregation calculates the average value for a field. The following SQL statement is executed in the background: AVG(price).

Count aggregation

The count aggregation allows you to determine the number of entries in a field that contain a value. The following SQL statement is executed in the background: COUNT(DISTINCT(manufacturerId)).

Max aggregation

The max aggregation returns the maximum value of a field. The following SQL statement is executed in the background: MAX(price).

Min aggregation

The min aggregation returns the minimum value of a field. The following SQL statement is executed in the background: MIN(price).

Sum aggregation

The sum aggregation allows you to compute the total of a field. The following SQL statement is executed in the background: SUM(price).

Stats aggregation

The stats aggregation allows you to calculate multiple values for a field at once. This includes the previous max, min, avg, and sum aggregations. The following SQL statement is executed in the background: SELECT MAX(price), MIN(price), AVG(price), SUM(price).

Terms aggregation

The terms aggregation belongs to the bucket aggregations. This allows you to determine the values of a field. The result contains each value once, along with how often it occurs. The terms aggregation also supports the following parameters:

• limit - Defines a maximum number of entries to be returned (default: zero)
• sort - Defines the order of the entries. By default, the following is not sorted
• aggregation - Enables you to calculate further aggregations for each key

The following SQL statement is executed in the background: SELECT DISTINCT(manufacturerId) as key, COUNT(manufacturerId) as count.

Filter aggregation

The filter aggregation belongs to the bucket aggregations. Unlike all other aggregations, this one does not produce a result. It can't be used alone. It is used only further to restrict the result of an aggregation in a criterion. Filters defined inside the filter property of this aggregation type are only used when calculating this aggregation. The filters have no effect on other aggregations or on the search results.

Entity aggregation

The entity aggregation is similar to the terms aggregation. It belongs to the bucket aggregations. As with terms aggregation, all unique values are determined for a field. The aggregation then uses the determined keys to load the defined entity. The keys are used here as IDs.

Histogram aggregation

The histogram aggregation is used as soon as the data to be determined refers to a date field. For histogram aggregation, one of the following date intervals can be specified: minute, hour, day, week, month, quarter, year, day. This interval groups the results and calculates the corresponding count of hits.

Range aggregations

Allows for aggregation of data on a predefined range of values for more flexibility in the DAL - for example, it provides faceted filters on a predefined range.

• from will be compared with greater than or equal to
• to will be compared with lower than

Nesting aggregations

A metric aggregation calculates the value for a specific field. This can be a total or, for example, a minimum or maximum value of the field. Bucket aggregations are different. This determines how often a value occurs in a search result and returns the count along with it. The special thing about bucket aggregation is that it can contain further aggregations. This allows the API to perform complex queries, like, for example:

• Calculate the number of manufacturers per category that have a price over 500 euros. *