Usage

derived_table: {
  create_process: {
    sql_step:
      CREATE TABLE ${SQL_TABLE_NAME}
      (customer_id int(11),
      lifetime_orders int(11)) ;;
    sql_step:
      INSERT INTO ${SQL_TABLE_NAME}
      (customer_id,
      lifetime_orders)
      SELECT customer_id, COUNT(*)
      AS lifetime_orders
      FROM order
      GROUP BY customer_id ;;
  }
}

Hierarchy

View File

view

derived_table

create_process

Default Value

None

Accepts

One or more sql_step subparameters

Definition

If your database dialect uses custom Data Definition Language (DDL) commands, you can use create_process to create persistent derived tables (PDTs). create_process defines a list of SQL statements that will be executed in the order listed. Each individual SQL statement is specified using the sql_step subparameter. Each sql_step subparameter can include any legal SQL query. You can define multiple sql_step subparameters, and they will be executed one at a time, in the order they are specified. Looker issues the statements in the sql_step subparameters as is, without Looker’s usual error correction.

For example, some database dialects don’t support CREATE TABLE as SELECT issued as a single SQL statement; they require separate SQL statements. As a result, traditional SQL-based persistent derived tables can’t be created on these dialects. The create_process parameter provides an alternate way to create PDTs, by creating a list of separate SQL statements that are issued in sequence.

You can also use create_process to support dialects such as Google’s predictive BigQuery ML (BQML) machine learning models.

The create_process parameter indicates that you are writing the full CREATE statements for the derived table, including any indexes. To add an index for a derived table with create_process, use a sql_step parameter to specify the SQL for the index.

For PDTs defined using create_process, you cannot use any of the following parameters:

Example

Create a ctasless_customer_order_facts persistent derived table on a MySQL database in two steps. First, issue the CREATE TABLE SQL statement, defined by the first sql_step subparameter. Second, issue the INSERT INTO SQL statement with a SELECT statement, defined by the second sql_step subparameter:

view: ctasless_customer_order_facts { derived_table: { datagroup_trigger: some_datagroup create_process: { sql_step: CREATE TABLE ${SQL_TABLE_NAME} ( customer_id int(11), lifetime_orders int(11) ) ;; sql_step: INSERT INTO ${SQL_TABLE_NAME}(customer_id, lifetime_orders) SELECT customer_id, COUNT(*) AS lifetime_orders FROM order GROUP BY customer_id ;; } } }

Things to consider

`${SQL_TABLE_NAME}` substitution operator

You can use the ${SQL_TABLE_NAME} substitution operator to substitute in the computed name of the PDT being created. This ensures the SQL statement will correctly include the PDT name given in the LookML view parameter.

create_process must create a table with the name indicated by the ${SQL_TABLE_NAME} substitution operator, or it will be rebuilt from scratch on every trigger check interval specified in a connection’s PDT and Datagroup Maintenance Schedule setting (the default is five minutes). This can cause unexpected query traffic on your database or data warehouse.

Use `sql_create` to create a PDT in one step

If your database dialect requires custom DDL commands, and you want to create a PDT in a single step, you can use sql_create to define a full SQL CREATE statement to execute and create a PDT in a single step.

Tables defined with `create_process` can’t be used for incremental PDTs

To be used as an incremental PDT, a SQL-based PDT must have a query defined using the sql parameter. SQL-based PDTs that are defined with the sql_create parameter or the create_process parameter cannot be incrementally built.

This is because Looker uses an INSERT or a MERGE command to create the increments for an incremental PDT. The derived table cannot be defined using custom Data Definition Language (DDL) statements, since Looker wouldn’t be able to determine which DDL statements would be required to create an accurate increment.

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