LookML terms and concepts

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This page defines the following core terms and concepts, which you will likely encounter often during LookML development:

Looks and user-defined dashboards are not described on this page, as users create them without using any LookML. However, their queries rely on the underlying LookML elements that are discussed on this page.

See the Looker glossary for a comprehensive list of terms and definitions used throughout Looker. For a comprehensive overview of the LookML parameters you can use in a LookML project, see the LookML quick reference page.

LookML project

In Looker, a project is a collection of files that describe the objects, connections, and user interface elements that will be used to carry out SQL queries. At the most basic level, these files describe how your database tables relate to each other and how Looker should interpret them. They may also include LookML parameters that define or change the options presented in Looker's UI. Each LookML project resides in its own Git repository for version control.

Once you connect Looker to your database, you can specify the database connection to use for your Looker project:

You can access your projects from the Develop section of the Looker navigation:

LookML projects are listed in the develop section of the Looker navigation.

See the Creating a new LookML project for information on creating a new project, and see the Accessing and editing project information for information on accessing and making changes to existing LookML projects.

Parts of a project

A LookML project can contain models, views, and LookML dashboards, each of which is made up other LookML elements.

As shown in the diagram above, the following are some of the more common types of files in a LookML project:

  • A model contains information about which tables to use and how they should be joined together. Here you'll typically define the model, its Explores, and its joins.
  • A view contains information about how to access or calculate information from each table (or across multiple joined tables). Here you'll typically define the view, its dimensions and measures, and its field sets.
  • An Explore is often defined within a model file, but sometimes you need a separate Explore file for a derived table or to extend or refine an Explore across models.
  • A manifest file can contain instructions for using files imported from another project or for your project's localization settings.

In addition to the above types of files, a project can have other types of files related to things like built-in dashboards, documentation, localization, and more. See the LookML project files documentation page for more information about these types of files as well as the other types of files you can have in your LookML project.

These files together make up one project. If you are using Git for version control, then each project is typically backed up by its own Git repository.

Where do LookML projects and files come from?

The most common way to create LookML files is to generate a LookML project from your database. You can also create a blank project and manually create its LookML files, or you can create a project by cloning an existing Git repository.

When you generate a new project from your database, Looker creates a baseline set of files that you can use as a template for building out the project:

  • Multiple view files, one file for every table in the database.
  • One model file. The model file declares an Explore for every view. Each Explore declaration includes join logic to join any view that Looker can determine is related to the Explore.

From here, you can customize the project by removing unwanted views and Explores and by adding custom dimensions and measures.

Major LookML structures

As shown in the preceding diagram, a project typically contains one or more model files that contain parameters defining a model and its Explores and joins. In addition, projects typically contain one or more view files, each containing parameters defining that view and its fields (including dimensions and measures) and sets of fields. The project can also contain a project manifest file containing parameters to use view files from other projects or configure localization defaults. This section describes those major structures.

Model

A model is a customized portal into the database, designed to provide intuitive data exploration for specific business users. Multiple models can exist for the same database connection in a single LookML project. Each model can expose different data to different users. For example, sales agents need different data than company executives, and so you would probably develop two models to offer views of the database appropriate for each user.

A model specifies a connection to a single database. A developer also defines a model's Explores within the model file. In Looker, queries are grouped by the model to which they belong. Your users see models listed under the Explore menu:

See the Types of files in a LookML project documentation page for more information about model files, including the structure and general syntax of model files.

See the Model parameters documentation page for details about the LookML parameters that can be used in a model file.

View

A view declaration defines a list of fields (dimensions or measures) and their linkage to an underlying table or derived table. In LookML a view typically references an underlying database table, but it can also represent a derived table.

A view may join to other views. The relationship between views is typically defined as part of an Explore declaration in a model file.

In Looker, view names appear at the beginning of dimension and measure names in the data table. This naming convention makes it clear which view the field belongs to:

See the Types of files in a LookML project documentation for more information about view files, including the structure and general syntax of view files.

See the View parameters documentation page for details about the LookML parameters that can be used in a view file.

Explore

An Explore is a view that users can query. You can think of the Explore as a starting point for a query, or in SQL terms, as the FROM in a SQL statement. Not all views are Explores, because not all views describe an entity of interest. For example, a States view corresponding to a lookup table for state names doesn't warrant an Explore, because business users never need to query it directly. On the other hand, business users probably want a way to query an Orders view, and so defining an Explore for Orders makes sense.

In Looker, your users can see Explores listed in the Explore menu:

By convention, Explores are declared in the model file with the explore parameter. In this following example of a model file, the orders Explore for an e-commerce database is defined within the model file. The views orders and customers that are referenced within the explore declaration are defined elsewhere, in their respective view files.

connection: order_database
include: "filename_pattern"

explore: orders {
  join: customers {
    sql_on: ${orders.customer_id} = ${customers.id} ;;
  }
}

In the example above, the connection parameter is used to specify the database connection for the model, and the include parameter is used to specify the files that will be available for the model to reference.

The explore declaration in the example above also specifies join relationships between views. For details on join declarations, visit the section on joins on this page. Visit the Join parameters documentation page for more details about the LookML parameters that can be used with the join parameter.

Dimension and measure fields

Views contain fields, mostly dimensions and measures, which are the fundamental building blocks for Looker queries.

In Looker, a dimension is a groupable field and can be used to filter query results. It can be:

  • An attribute, which has a direct association to a column in an underlying table
  • A fact or numerical value
  • A derived value, computed based on the values of other fields in a single row

In Looker, dimensions always appear in the GROUP BY clause of the SQL that Looker generates.

For example, dimensions for a Products view might include product name, product model, product color, product price, product created date, and product end-of-life date.

A measure is a field that uses a SQL aggregate function, such as COUNT, SUM, AVG, MIN, or MAX. Any field computed based on the values of other measure values is also a measure. Measures can be used to filter grouped values. For example, measures for a Sales view might include total items sold (a count), total sale price (a sum), and average sale price (an average).

The behavior and expected values for a field depend on its declared type, such as string, number, or time. For measures, types include aggregate functions, such as sum and percent_of_previous. For details, refer to dimension types and measure types.

In Looker, fields are listed on the Explore page in the field picker on the left-hand side of the page.

By convention, fields are declared as part of the view they belong to, stored in a view file. The following example shows several dimension and measure declarations. Notice the use of the substitution operator ($) to reference fields without using a fully scoped SQL column name.

Here are some example declarations of dimensions and measures:

view: orders {
  dimension: id {
    primary_key: yes
    type: number
    sql: ${TABLE}.id ;;
  }
  dimension: customer_id {
    sql: ${TABLE}.customer_id ;;
  }
  dimension: amount {
    type: number
    value_format: "0.00"
    sql: ${TABLE}.amount ;;
  }
  dimension_group: created {
    type: time
    timeframes: [date, week]
    sql: ${TABLE}.created_at ;;
  }
  measure: count {
    type: count           # creates sql COUNT(orders.id)
    sql: ${id} ;;
  }
  measure: total_amount {
    type: sum             # creates sql SUM(orders.amount)
    sql: ${amount} ;;
  }
}

You can also define a dimension_group, which creates multiple time-related dimensions at once, and filter fields, which have a variety of advanced use cases such as templated filters.

See the Field parameters documentation page for complete details on declaring fields and the various settings that can be applied to them.

Joins

As part of an explore declaration, each join declaration specifies a view that can be joined into the Explore. When a user creates a query that includes fields from multiple views, Looker automatically generates SQL join logic to bring in all fields correctly.

Here is an example join in an explore declaration:

# file: ecommercestore.model.lookml

connection: order_database
include: "filename_pattern"   # include all the views

explore: orders {
  join: customers {
    sql_on: ${orders.customer_id} = ${customers.id} ;;
  }
}

For more details, visit the Working with joins in LookML documentation page.

Project manifest files

Your project may contain a project manifest file, which is used for project-level settings such as those for specifying other projects to import into the current project, defining LookML constants, specifying model localization settings, and adding extensions and custom visualizations to your project.

Each project can have only one manifest file. The file must be named manifest.lkml and be located at the root level of your Git repo. When you're using folders in the IDE, be sure that the manifest.lkml file is kept at the root level of your project's directory structure.

To import LookML files from a different project, use the project manifest file to specify a name for your current project and the location of any external projects, which could be stored locally or remotely. For example:

# This project
project_name: "my_project"

# The project to import
local_dependency: {
  project: "my_other_project"
}

remote_dependency: ga_360_block {
  url: "https://github.com/llooker/google_ga360"
  ref: "4be130a28f3776c2bf67a9acc637e65c11231bcc"
}

After defining the external projects in the project manifest file, you can use the include parameter in your model file to add files from those external project to your current project. For example:

include: "//my_other_project/imported_view.view"
include: "//ga_360_block/*.view"

For more information, see the Importing files from other projects documentation page.

To add localization to your model, use the project manifest file to specify default localization settings. For example:

localization_settings: {
  default_locale: en
  localization_level: permissive
}

Specifying default localization settings is one step in localizing your model. For more information, see the Localizing your LookML model documentation page.

Sets

In Looker, a set is a list that defines a group of fields that are used together. Typically sets are used to specify which fields to display after a user drills down into data. Drill sets are specified on a field-by-field basis, so you get complete control over what data is displayed when a user clicks a value in a table or dashboard. Sets can also be used as a security feature to define groups of fields visible to specific users.

The following example shows a set declaration in a view order_items, defining fields that list relevant details about a purchased item. Note that the set references fields from other views by specifying scope.

set: order_items_stats_set {
  fields: [
    id,  # scope defaults to order_items view
    orders.created_date,  # scope is "orders" view
    orders.id,
    users.name,
    users.history,  # show all products this user has purchased
    products.item_name,
    products.brand,
    products.category,
    total_sale_price
  ]
}

See the set parameter documentation page for complete usage details for sets.

Drill down

In Looker, you can drill down on any fields that are set up that way when writing LookML. Drilling works in both query results tables and dashboards. Drilling starts a new query that is restricted by the value you clicked on.

Drill behavior is different for dimensions and measures:

  • When drilling on a dimension, the new query filters on the drilled value. For example, if you click on a specific date in a query of customer orders by date, the new query will show orders only on the specific date.
  • When drilling on a measure, the new query will show the dataset that contributed to the measure. For example, when drilling on a count, the new query will show the rows to calculate that count. When drilling on max, min, and average measures, drilling still shows all the rows that contributed to that measure. This means that drilling on a max measure, for example, shows all the rows that were used to calculate the max value, not just a single row for the max value.

The fields to show for the new drill query can be defined by a set, or can be defined by the drill_fields parameter (for fields) or the drill_fields parameter (for views).

Derived tables

A derived table is a query whose results are used as if it were an actual table in the database. Derived tables are created by using the derived_table parameter in a view declaration. Looker accesses derived tables as though they were physical tables with their own set of columns. A derived table is exposed as its own view using the derived_table parameter, and defines dimensions and measures in the same manner as conventional views. The view for a derived table can be queried and joined into other views, just like any other view.

Derived tables can also be defined as persistent derived tables (PDTs), which are derived tables that are written into a scratch schema on your database and automatically regenerated on the schedule that you specify with a persistence strategy.

See the Derived tables in Looker documentation page for more information.

Database connection

Another important element of a LookML project is the database connection that Looker will use to run queries on your database. A Looker admin uses the Connections page to configure database connections, and LookML developers use the connection parameter in a model file to specify which connection to use for the model. If you generate a LookML project from your database, Looker will automatically populate the connection parameter in the model file.

Case sensitivity

LookML is case-sensitive, so be sure to match the case when referring to LookML elements. Looker will alert you if you have referred to an element that doesn't exist. In the example below, the developer has incorrectly capitalized "FLIGHTS." The Looker IDE shows a warning that the e_FLIGHTS_pdt does not exist. In addition, the IDE suggests the name of an existing Explore, which is e_flights_pdt:

However, if your project contained both e_FLIGHTS_pdt and e_flights_pdt, the Looker IDE would not be able to correct you, so you would have to be sure which version you intended. Generally, it's a good idea to stick with lowercase when naming LookML objects.

IDE folder names are also case-sensitive. You must match the capitalization of folder names whenever you specify file paths. For example, if you have a folder named Views, you must use this same capitalization in the include parameter. Again, the Looker IDE will indicate an error if your capitalization doesn't match an existing folder in your project: