Content Comparison

Problem

• Query only needs a subset of the data from some entities, such as a summary of orders for several customers without all of the order details. How to extract data from relevant entities.

Solution

• Typical uses of the events published by the event store are to maintain materialized views of entities as actions in the application change them, and for integration with external systems.

• Materialized views, which only contain data required by a query, allow applications to quickly obtain the information they need.

• Data it contains is completely disposable because it can be entirely rebuilt from the source data stores.

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Materialized View in Practice

CREATE MATERIALIZED VIEW user_purchase_summary AS SELECT
  u.id as user_id,
  COUNT(*) as total_purchases,
  SUM(CASE when p.status = 'cancelled' THEN 1 ELSE 0 END) as cancelled_purchases
FROM users u
JOIN purchases p ON p.user_id = u.id;