Materialized Views

Transform data with Materialized Views.

In ClickHouse, Materialized Views are the primary way to transform data. They are a persisted query result that is automatically updated when the underlying data changes.

You can use them to reshape, filter, or enrich data from one or more source Data Pools into a new Data Pool. For example, you could create a Materialized View that:

• Flattens nested JSON into tabular form
• Flattens JSON array into individual rows
• Combines data from multiple source Data Pools through JOINs
• Calculates new derived columns from existing data
• Performs incremental aggregations
• Sorts rows with a different sorting key
• Filters out unnecessary data based on conditions
• De-duplicates rows

The transformed data in the destination Data Pool is automatically kept up-to-date as the underlying source data changes.

How do Materialized Views work?

Materialized Views in ClickHouse work by automatically executing a specified SQL query over new data inserted into a source Data Pool and writing the query results into a destination Data Pool.

When creating a Materialized View, you define a SELECT query that transforms or aggregates data from one or more source Data Pools. You also define a destination Data Pool where the resulting data will be written.

Whenever new rows are inserted into the source Data Pools, Propel automatically triggers the Materialized View SQL query over just the new data and writes the results to the destination Data Pool. This allows incrementally updating the destination data Pool without re-computing the entire query from scratch.

Setting the Materialized View’s destination to a SummingMergeTree or AggregatingMergeTree Data Pool enables efficient incremental updates and storage of aggregations.

Materialized Views can be chained, with one Materialized View reading from the destination Data Pool of another, enabling multi-stage data transformation pipelines.

Creating a Materialized View

This section provides step-by-step instructions on creating a Materialized View in the Console, the API, and Terraform.

Console

To start, go to the “Materialized Views” section of the Console, then click on “Create new Materialized View”.

First, you need to enter the SQL query that will define the transformation. Once you have the query ready, click “Continue”.

For this example, we are going to create a new Data Pool, so select “New Data Pool” and give it a name.

For this example, we are going to use the “Append-only data” settings. Answer the questions to generate the table settings. Select the “timestamp” column on the first question and click “Continue”.

Here, you will see your recommended table settings. Click “Continue”.

To learn more, see our How to select a table engine and sorting key guide.

Next, decide whether you want to backfill the existing data in the source Data Pool to the destination Data Pool. In most cases, you’d want to backfill. Propel takes care of this process for you.

Lastly, give your Materialized View a name and description.

You’ll notice the new Data Pool is created with the new schema and data.

Click on the “Preview Data” tab to see your transformed records.

API

mutation {
  createMaterializedView(input: {
    uniqueName: "TacoSoft order item ID and name Materialized View",
    description: "Order items with only name and timestamp",
    sql: """
      SELECT
        timestamp,
        order_item_id,
        taco_name
      FROM "TacoSoft Demo Data";
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "timestamp"
        },
        uniqueName: "taco_order_item_and_name",
        accessControlEnabled: true
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
      id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "my_materialized_view" {
  unique_name = "TacoSoft order item ID and name Materialized View"
  description = "Order items with only name and timestamp"

  sql = <<-SQL
  SELECT
    timestamp,
    order_item_id,
    taco_name
  FROM "TacoSoft Demo Data";
  SQL

  new_data_pool {
    unique_name            = "taco_order_item_and_name"
    timestamp              = "timestamp"
    access_control_enabled = true
  }

  backfill = true
}

---

Materialized View examples

In this section, we will provide examples of common use cases solved with Materialized Views.

For all the examples, we’ll use a source Data Pool called events with two columns:

• _propel_received_at (TIMESTAMP)
• _propel_payload (JSON)

To replicate the examples, create a Webhook Data Pool with just the _propel_received_at and _propel_payload columns. Then click on the Data Pool, click on “Schema” tab and paste the event below to create sample records.

The JSON events in the _propel_payload column are of the form:

{
  "customer_id": 5,
  "order_id": 34,
  "store_id": 4445,
  "order_details": {
    "taco_count": 7,
    "price": 25.90,
    "checkout_time": "2023-07-31T15:20:10Z"
  },
  "created_at": "2023-07-31T14:50:35Z"
}

For the API examples, you can copy and paste them to the API Playground.

Example 1: Flatten nested JSON into tabular form

The following Materialized View flattens the JSON into individual columns. In Propel, you can access nested JSON keys by using dot notation, as shown in the example below. We are also using the parseDateTimeBestEffort function to parse the timestamp from a string to ClickHouse timestamp.

SQL

Destination Data Pool
Table Engine	MergeTree
Sorting Key	created_at

SELECT
  _propel_received_at,
  "_propel_payload.customer_id" AS customer_id,
  "_propel_payload.order_id" AS order_id,
  "_propel_payload.store_id" AS store_id,
  "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
  "_propel_payload.order_details.price"::DOUBLE AS price,
  parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
  parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
FROM events

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Events Materialized View",
    description: "Flattens JSON into columns",
    sql: """
      SELECT
        _propel_received_at,
        "_propel_payload.customer_id" AS customer_id,
        "_propel_payload.order_id" AS order_id,
        "_propel_payload.store_id" AS store_id,
        "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
        "_propel_payload.order_details.price"::DOUBLE AS price,
        parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
        parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
      FROM events
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "created_at"
        },
        uniqueName: "flattened_events",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            mergeTree: {
              type: MERGE_TREE
            }
          }
          orderBy: ["created_at"]
        }
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "events_materialized_view" {
  unique_name = "Events Materialized View"
  description = "Flattens JSON into columns"

  sql = <<-SQL
  SELECT
    _propel_received_at,
    "_propel_payload.customer_id" AS customer_id,
    "_propel_payload.order_id" AS order_id,
    "_propel_payload.store_id" AS store_id,
    "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
    "_propel_payload.order_details.price"::DOUBLE AS price,
    parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
    parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
  FROM events
  SQL

  new_data_pool {
    unique_name            = "flattened_events"
    timestamp              = "created_at"
    access_control_enabled = true

    table_settings {
      engine {
        type = "MERGE_TREE"
      }
      order_by = ["created_at"]
    }
  }

  backfill = true
}

---

Example 2: Flatten JSON array into individual rows

The following Materialized View flattens a JSON array into rows.

Given a table TacoOrders with the following schema:

id (UInt32)
orderDetails (JSON)

With the following data:

(1, '{"orderId": 101, "orderDate": "2024-08-01", "customerName": "John Doe", "customerDetails": [{"name": "John", "address": "123 Taco St", "orderItem": "Taco Al Pastor", "quantity": 3, "price": 9.99}]}'),
(2, '{"orderId": 102, "orderDate": "2024-08-01", "customerName": "Jane Smith", "customerDetails": [{"name": "Jane", "address": "456 Burrito Blvd", "orderItem": "Taco Carnitas", "quantity": 2, "price": 8.99}]}'),
(3, '{"orderId": 103, "orderDate": "2024-08-01", "customerName": "Alice Johnson", "customerDetails": [{"name": "Alice", "address": "789 Quesadilla Ln", "orderItem": "Taco de Pescado", "quantity": 1, "price": 7.99}]}'),
(4, '{"orderId": 104, "orderDate": "2024-08-02", "customerName": "Bob Brown", "customerDetails": [{"name": "Bob", "address": "101 Tostada Ave", "orderItem": "Taco de Pollo", "quantity": 4, "price": 10.99}]}'),
(5, '{"orderId": 105, "orderDate": "2024-08-02", "customerName": "Carol White", "customerDetails": [{"name": "Carol", "address": "202 Enchilada Dr", "orderItem": "Taco Vegetariano", "quantity": 2, "price": 6.99}]}'),
(6, '{"orderId": 106, "orderDate": "2024-08-02", "customerName": "David Green", "customerDetails": [{"name": "David", "address": "303 Salsa Rd", "orderItem": "Taco de Chorizo", "quantity": 5, "price": 11.99}]}'),
(7, '{"orderId": 107, "orderDate": "2024-08-03", "customerName": "Eve Black", "customerDetails": [{"name": "Eve", "address": "404 Guacamole St", "orderItem": "Taco Al Pastor", "quantity": 3, "price": 9.99}]}'),
(8, '{"orderId": 108, "orderDate": "2024-08-03", "customerName": "Frank Brown", "customerDetails": [{"name": "Frank", "address": "505 Tortilla Blvd", "orderItem": "Taco Carnitas", "quantity": 2, "price": 8.99}]}'),
(9, '{"orderId": 109, "orderDate": "2024-08-03", "customerName": "Grace Blue", "customerDetails": [{"name": "Grace", "address": "606 Pico de Gallo Rd", "orderItem": "Taco de Pescado", "quantity": 1, "price": 7.99}]}'),
(10, '{"orderId": 110, "orderDate": "2024-08-04", "customerName": "Hank Yellow", "customerDetails": [{"name": "Hank", "address": "707 Jalapeño Ln", "orderItem": "Taco de Pollo", "quantity": 4, "price": 10.99}]}');

SQL

Destination Data Pool
Table Engine	MergeTree
Sorting Key	orderDate

SELECT
  JSONExtract(orderDetails, 'orderId', 'UInt32') as orderId,
  JSONExtract(orderDetails, 'orderDate', 'String') as orderDate,
  JSONExtract(orderDetails, 'customerName', 'String') as customerName,
  JSONExtract(record, 'name', 'String') AS name,
  JSONExtract(record, 'address', 'String') AS address,
  JSONExtract(record, 'orderItem', 'String') AS orderItem,
  JSONExtract(record, 'quantity', 'UInt32') AS quantity,
  JSONExtract(record, 'price', 'Float64') AS price
FROM (
  SELECT
    orderDetails,
    arrayJoin(JSONExtractArrayRaw(orderDetails, 'customerDetails')) AS record
  FROM TacoOrders
) AS t;

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Events Materialized View",
    description: "Flattens JSON into columns",
    sql: """
      SELECT
        JSONExtract(orderDetails, 'orderId', 'UInt32') as orderId,
        JSONExtract(orderDetails, 'orderDate', 'String') as orderDate,
        JSONExtract(orderDetails, 'customerName', 'String') as customerName,
        JSONExtract(record, 'name', 'String') AS name,
        JSONExtract(record, 'address', 'String') AS address,
        JSONExtract(record, 'orderItem', 'String') AS orderItem,
        JSONExtract(record, 'quantity', 'UInt32') AS quantity,
        JSONExtract(record, 'price', 'Float64') AS price
      FROM (
        SELECT
          orderDetails,
          arrayJoin(JSONExtractArrayRaw(orderDetails, 'customerDetails')) AS record
        FROM TacoOrders
      ) AS t;
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "orderDate"
        },
        uniqueName: "flattened_rows",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            mergeTree: {
              type: MERGE_TREE
            }
          }
          orderBy: ["orderDate"]
        }
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "events_materialized_view" {
  unique_name = "Events Materialized View"
  description = "Flattens JSON into columns"

  sql = <<-SQL
  SELECT
    JSONExtract(orderDetails, 'orderId', 'UInt32') as orderId,
    JSONExtract(orderDetails, 'orderDate', 'String') as orderDate,
    JSONExtract(orderDetails, 'customerName', 'String') as customerName,
    JSONExtract(record, 'name', 'String') AS name,
    JSONExtract(record, 'address', 'String') AS address,
    JSONExtract(record, 'orderItem', 'String') AS orderItem,
    JSONExtract(record, 'quantity', 'UInt32') AS quantity,
    JSONExtract(record, 'price', 'Float64') AS price
  FROM (
    SELECT
      orderDetails,
      arrayJoin(JSONExtractArrayRaw(orderDetails, 'customerDetails')) AS record
    FROM TacoOrders
  ) AS t;
  SQL

  new_data_pool {
    unique_name            = "flattened_events"
    timestamp              = "orderDate"
    access_control_enabled = true

    table_settings {
      engine {
        type = "MERGE_TREE"
      }
      order_by = ["orderDate"]
    }
  }

  backfill = true
}

---

Example 3: Combines data from multiple source tables through JOINs

Given an additional table stores with two columns,

store_id (STRING)
name (STRING)

The Materialized view below performs a JOIN to enrich the event with the store name.

Materialized Views trigger off the left-most table of the join which is considered the source Data Pool. The Materialized View will pull values from right-side tables in the join but will not trigger if those tables change.

SQL

Destination Data Pool
Table Engine	MergeTree
Sorting Key	created_at

SELECT
  e._propel_received_at,
  e."_propel_payload.customer_id" AS customer_id,
  e."_propel_payload.order_id" AS order_id,
  e."_propel_payload.store_id" AS store_id,
  s.store_name AS store_name,
  e."_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
  e."_propel_payload.order_details.price"::DOUBLE AS price,
  e.parseDateTimeBestEffort(e."_propel_payload.order_details.checkout_time") AS checkout_time,
  e.parseDateTimeBestEffort(e."_propel_payload.created_at") AS created_at
FROM events e
LEFT JOIN store s on e."_propel_payload.store_id" = s.store_id

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Enriched Events Materialized View",
    description: "Flattens and enriches JSON into columns",
    sql: """
      SELECT
        e._propel_received_at,
        e."_propel_payload.customer_id" AS customer_id,
        e."_propel_payload.order_id" AS order_id,
        e."_propel_payload.store_id" AS store_id,
        s.store_name AS store_name,
        e."_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
        e."_propel_payload.order_details.price"::DOUBLE AS price,
        e.parseDateTimeBestEffort(e."_propel_payload.order_details.checkout_time") AS checkout_time,
        e.parseDateTimeBestEffort(e."_propel_payload.created_at") AS created_at
      FROM events e
      LEFT JOIN store s on e."_propel_payload.store_id" = s.store_id
    """,
    destination:{
      newDataPool:{
        timestamp:{
          columnName: "created_at"
        },
        uniqueName: "flattened_enriched_events",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            mergeTree: {
              type: MERGE_TREE
            }
          }
          orderBy: ["created_at"]
        }
      }
    },
    backfillOptions:{
      backfill: true
    }
  }) {
      materializedView {
	      id
        sql
        uniqueName
      }
  }
}

Terraform

resource "propel_materialized_view" "enriched_events_materialized_view" {
  unique_name = "Enriched Events Materialized View"
  description = "Flattens and enriches JSON into columns"

  sql = <<-SQL
  SELECT
    e._propel_received_at,
    e."_propel_payload.customer_id" AS customer_id,
    e."_propel_payload.order_id" AS order_id,
    e."_propel_payload.store_id" AS store_id,
    s.store_name AS store_name,
    e."_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
    e."_propel_payload.order_details.price"::DOUBLE AS price,
    e.parseDateTimeBestEffort(e."_propel_payload.order_details.checkout_time") AS checkout_time,
    e.parseDateTimeBestEffort(e."_propel_payload.created_at") AS created_at
  FROM events e
  LEFT JOIN store s on e."_propel_payload.store_id" = s.store_id
  SQL

  new_data_pool {
    unique_name            = "flattened_enriched_events"
    timestamp              = "created_at"
    access_control_enabled = true

    table_settings {
      engine {
        type = "MERGE_TREE"
      }
      order_by = ["created_at"]
    }
  }

  backfill = true
}

---

Example 4: Calculates new derived columns from existing data

This Materialized View calculates the total price multiplying the taco_count times the price column.

SQL

Destination Data Pool
Table Engine	MergeTree
Sorting Key	created_at

SELECT
  _propel_received_at,
  "_propel_payload.customer_id" AS customer_id,
  "_propel_payload.order_id" AS order_id,
  "_propel_payload.store_id" AS store_id,
  "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
  "_propel_payload.order_details.price"::DOUBLE AS price,
  parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
  parseDateTimeBestEffort("_propel_payload.created_at") AS created_at,
  round("_propel_payload.order_details.taco_count"::INTEGER * "_propel_payload.order_details.price"::DOUBLE, 2) AS total_price
FROM events

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Events Materialized View",
    description: "Flattens JSON and calculates total price",
    sql: """
      SELECT
        _propel_received_at,
        "_propel_payload.customer_id" AS customer_id,
        "_propel_payload.order_id" AS order_id,
        "_propel_payload.store_id" AS store_id,
        "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
        "_propel_payload.order_details.price"::DOUBLE AS price,
        parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
        parseDateTimeBestEffort("_propel_payload.created_at") AS created_at,
        round("_propel_payload.order_details.taco_count"::INTEGER * "_propel_payload.order_details.price"::DOUBLE, 2) AS total_price
      FROM events
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "created_at"
        },
        uniqueName: "flattened_events",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            mergeTree: {
              type: MERGE_TREE
            }
          }
          orderBy: ["created_at"]
        }
      }
    }
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "events_materialized_view" {
  unique_name = "Events Materialized View"
  description = "Flattens JSON and calculates total price"

  sql = <<-SQL
  SELECT
    _propel_received_at,
    "_propel_payload.customer_id" AS customer_id,
    "_propel_payload.order_id" AS order_id,
    "_propel_payload.store_id" AS store_id,
    "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
    "_propel_payload.order_details.price"::DOUBLE AS price,
    parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
    parseDateTimeBestEffort("_propel_payload.created_at") AS created_at,
    round("_propel_payload.order_details.taco_count"::INTEGER * "_propel_payload.order_details.price"::DOUBLE, 2) AS total_price
  FROM events
  SQL

  new_data_pool {
    unique_name            = "flattened_events"
    timestamp              = "created_at"
    access_control_enabled = true

    table_settings {
      engine {
        type = "MERGE_TREE"
      }
      order_by = ["created_at"]
    }
  }

  backfill = true
}

---

Example 5: Perform incremental aggregations

The Materialized View below incrementally aggregates the number of tacos sold and sales by customer_id and month. This Materialized View uses the SummingMergeTree table engine to incrementally aggregate rows as they are written. To learn more, read our guide on How to select a table engine and sorting key.

SQL

Destination Data Pool
Table Engine	SummingMergeTree
Sorting Key	month

SELECT
  toStartOfMonth(parseDateTimeBestEffort("_propel_payload.created_at")) AS month,
  "_propel_payload.customer_id" AS customer_id,
  SUM("_propel_payload.order_details.taco_count"::INTEGER) AS taco_count,
  SUM(round("_propel_payload.order_details.taco_count"::INTEGER * "_propel_payload.order_details.price"::DOUBLE, 2)) AS total_sales
FROM events
GROUP BY
  toStartOfMonth(parseDateTimeBestEffort("_propel_payload.created_at")),
  customer_id

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Event Aggregation Materialized View",
    description: "Aggregates tacos sold and sales by customer by month",
    sql: """
      SELECT
        toStartOfMonth(parseDateTimeBestEffort("_propel_payload.created_at")) AS month,
        "_propel_payload.customer_id" AS customer_id,
        SUM("_propel_payload.order_details.taco_count"::INTEGER) AS taco_count,
        SUM(round("_propel_payload.order_details.taco_count"::INTEGER * "_propel_payload.order_details.price"::DOUBLE, 2)) AS total_sales
      FROM events
      GROUP BY
        toStartOfMonth(parseDateTimeBestEffort("_propel_payload.created_at")),
        customer_id
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "month"
        },
        uniqueName: "aggregated_events",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            summingMergeTree: {
              type: SUMMING_MERGE_TREE
            }
          }
          orderBy: ["month"]
        }
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "event_aggregation_materialized_view" {
  unique_name = "Event Aggregation Materialized View"
  description = "Aggregates tacos sold and sales by customer by month"

  sql = <<-SQL
  SELECT
    toStartOfMonth(parseDateTimeBestEffort("_propel_payload.created_at")) AS month,
    "_propel_payload.customer_id" AS customer_id,
    SUM("_propel_payload.order_details.taco_count"::INTEGER) AS taco_count,
    SUM(round("_propel_payload.order_details.taco_count"::INTEGER * "_propel_payload.order_details.price"::DOUBLE, 2)) AS total_sales
  FROM events
  GROUP BY
    toStartOfMonth(parseDateTimeBestEffort("_propel_payload.created_at")),
    customer_id
  SQL

  new_data_pool {
    unique_name            = "aggregated_events"
    timestamp              = "month"
    access_control_enabled = true

    table_settings {
      engine {
        type = "SUMMING_MERGE_TREE"
      }
      order_by = ["month"]
    }
  }

  backfill = true
}

---

Example 6: Sorts rows with a different sorting key

The Materialized View below creates a destination Data Pool with a different sorting key. It sorts the rows by the checkout_time column instead of the _propel_received_at column of the source Data Pool.

SQL

Destination Data Pool
Table Engine	MergeTree
Sorting Key	checkout_time

SELECT
  *,
  parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time
FROM events

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Events Materialized View",
    description: "Sorts by checkout_time",
    sql: """
      SELECT
        *,
        parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time
      FROM events
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "checkout_time"
        },
        uniqueName: "events_sorted_by_checkout_time",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            mergeTree: {
              type: MERGE_TREE
            }
          }
          orderBy: ["checkout_time"]
        }
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "events_materialized_view_sorted_by_checkout_time" {
  unique_name = "Events Materialized View"
  description = "Sorts by checkout_time"

  sql = <<-SQL
  SELECT
    *,
    parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time
  FROM events
  SQL

  new_data_pool {
    unique_name            = "events_sorted_by_checkout_time"
    timestamp              = "checkout_time"
    access_control_enabled = true

    table_settings {
      engine {
        type = "MERGE_TREE"
      }
      order_by = ["checkout_time"]
    }
  }

  backfill = true
}

---

Example 7: Filters out unnecessary data based on conditions

The Materialized View below filters out rows older than 2024.

SQL

Destination Data Pool
Table Engine	MergeTree
Sorting Key	created_at

SELECT
  *,
  parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
FROM events
WHERE parseDateTimeBestEffort("_propel_payload.created_at") > '2024-01-01'

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Events Materialized View",
    description: "Filters out older rows",
    sql: """
      SELECT
        *,
        parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
      FROM events
      WHERE parseDateTimeBestEffort("_propel_payload.created_at") > '2024-01-01'
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "created_at"
        },
        uniqueName: "filtered_events",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            mergeTree: {
              type: MERGE_TREE
            }
          }
          orderBy: ["created_at"]
        }
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "filtered_events_materialized_view" {
  unique_name = "Events Materialized View"
  description = "Filters out older rows"

  sql = <<-SQL
  SELECT
    *,
    parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
  FROM events
  WHERE parseDateTimeBestEffort("_propel_payload.created_at") > '2024-01-01'
  SQL

  new_data_pool {
    unique_name            = "filtered_events"
    timestamp              = "created_at"
    access_control_enabled = true

    table_settings {
      engine {
        type = "MERGE_TREE"
      }
      order_by = ["created_at"]
    }
  }

  backfill = true
}

---

Example 8: Deduplicating rows

The Materialized View below flattens and deduplicates events. It uses the ReplacingMergeTree table engine to duplicate events with the same sorting key. To learn more, read our guide on How to select a table engine and sorting key.

SQL

Destination Data Pool
Table Engine	ReplacingMergeTree
Sorting Key	created_at, order_ids

SELECT
  _propel_received_at,
  "_propel_payload.customer_id" AS customer_id,
  "_propel_payload.order_id" AS order_id,
  "_propel_payload.store_id" AS store_id,
  "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
  "_propel_payload.order_details.price"::DOUBLE AS price,
  parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
  parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
FROM events

API

mutation {
  createMaterializedView(input: {
    uniqueName: "Event Deduplication Materialized View",
    description: "Flattens JSON and deduplicates events",
    sql: """
      SELECT
        _propel_received_at,
        "_propel_payload.customer_id" AS customer_id,
        "_propel_payload.order_id" AS order_id,
        "_propel_payload.store_id" AS store_id,
        "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
        "_propel_payload.order_details.price"::DOUBLE AS price,
        parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
        parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
      FROM events
    """,
    destination: {
      newDataPool: {
        timestamp: {
          columnName: "created_at"
        },
        uniqueName: "deduplicated_events",
        accessControlEnabled: true
        tableSettings: {
          engine: {
            replacingMergeTree: {
              type: REPLACING_MERGE_TREE
            }
          }
          orderBy: ["created_at", "order_id"]
        }
      }
    },
    backfillOptions: {
      backfill: true
    }
  }) {
    materializedView {
	    id
      sql
      uniqueName
    }
  }
}

Terraform

resource "propel_materialized_view" "event_deduplication_materialized_view" {
  unique_name = "Event Deduplication Materialized View"
  description = "Flattens JSON and deduplicates events"

  sql = <<-SQL
  SELECT
    _propel_received_at,
    "_propel_payload.customer_id" AS customer_id,
    "_propel_payload.order_id" AS order_id,
    "_propel_payload.store_id" AS store_id,
    "_propel_payload.order_details.taco_count"::INTEGER AS taco_count,
    "_propel_payload.order_details.price"::DOUBLE AS price,
    parseDateTimeBestEffort("_propel_payload.order_details.checkout_time") AS checkout_time,
    parseDateTimeBestEffort("_propel_payload.created_at") AS created_at
  FROM events
  SQL

  new_data_pool {
    unique_name            = "deduplicated_events"
    timestamp              = "created_at"
    access_control_enabled = true

    table_settings {
      engine {
        type = "REPLACING_MERGE_TREE"
      }
      order_by = ["created_at", "order_id"]
    }
  }

  backfill = true
}

---

Frequently asked questions

What is the difference between materialized views and views?

In ClickHouse, a view is a virtual table based on the result set of a SELECT statement. It is used to simplify complex queries by breaking them up into manageable parts. A view always shows up-to-date data—the query is run every time the view is referenced in a query.

On the other hand, a Materialized View is a persisted version of a SELECT query’s result set, which is automatically updated when the data underlying the query changes.

Do Materialized Views transform data in real-time or on a schedule?

Materialized Views in ClickHouse transform data in real-time. Whenever new data is inserted into the source Data Pool, the Materialized View is automatically triggered to transform the new data and write the results to the destination Data Pool.

How much do Materialized Views cost?

Materialized Views do not have a cost per se, but they incur data write costs just like any other Data Pool. Similarly, the destination Data Pools consume storage just like any other Data Pool.

What happens if I delete a Materialized View?

If you delete a Materialized View in Propel, new data will stop being inserted into the destination Data Pool. The destination Data Pool associated with it will not be automatically deleted.

Can a Materialized View be modified?

In ClickHouse, Materialized Views cannot be directly modified. If you need to change the fields or the query, you would need to create a new Materialized View.

What happens if I update or delete data in the source Data Pool with the update or delete API?

Data deleted or updated with the Batch update or delete API will not trigger the Materialized View and will not be propagated to the destination Data Pool.