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2024-12-23 17:41:41 +00:00 · 2024-10-06 14:16:09 +08:00 · 2024-10-06 14:16:09 +08:00 · 6a18ee1f28
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+---
+language: dbt
+filename: learndbt.sql
+contributors:
+  - ["isabel faulds", "https://github.com/manyshapes"]
+
+---
+
+Data Build Tool or dbt™ (core) is an open-source command-line tool and framework
+for data transformation workflows. There is also a dbt cloud for managed, hosted
+ dbt services with extended capabilities. dbt (core) utilizes .sql, .py, .yml,
+ and .bash or any cli for orchestrating data warehouse command executions and
+generating .json artifacts.
+
+dbt is agnostic to cloud provider, warehouse, and sql dialect. dbt works most
+effectively with version controlled systems and is implemented commonly with
+[git](git.html.markdown). dbt leverages [jinja](jinja.html.markdown) functions
+for dynamic values within [yaml](yaml.html.markdown), [sql](sql.html.markdown)
+and [python](python.html.markdown) .
+
+### dbt SQL Models
+
+```sql
+-- models can have optional configs specified within them
+{{ config( 
+--  names in database will be filenames unless an alias
+    alias='report' ,
+--  models can be views, tables, incremental (updated tables), 
+-- ephemeral (temp tables), and snapshots (historical tables)
+    materialized='incremental',
+--  if incremental, data capture methods can be specified with a strategy 
+    incremental_strategy='delete+insert',
+    -- that can fail if the data schema changes
+    on_schema_change='fail'
+-- 
+)}}
+
+-- dbt emphasizes cte based development
+with staging_data as (
+    select * ,
+        current_timestamp() as loaded_date
+-- with refs to use other dbt seeds and models
+    from {{ ref('seed_data') }}
+)
+
+select
+    _id,
+    account_id,
+    transaction_date,
+    total_usd,
+    loaded_date
+
+from staging_data
+-- dbt can use {% if %} statements for conditional code block executions and
+-- is_incremental() to check if the current model is incremental
+{% if is_incremental() %}
+-- {{ this }} self references the current model
+where transaction_date > ( select max(transaction_date) from {{ this }} )
+-- the code block is not executed if the if statement is not met
+{% endif %}
+
+
+-- Snapshot models preserve historical data, or slowly changing dimensions
+{% snapshot snapshotted_model %}
+{{
+    config(
+-- specifying a unique id 
+        unique_key='_id'
+-- dbt will create new records for snapshotted data if there are changes in the
+-- tracked columns
+        strategy='check'
+        check_cols=['account_manager'],
+        snapshot_date='snapshot_date'
+    )
+}}
+
+with staging_data as (
+    select * from {{ ref('staging_account_transactions')}}
+),
+
+final as (
+    select
+        _id,
+        transaction_date,
+        account_id,
+    -- when a change is detected in account_manager a new row will be saved
+        account_manager,
+        -- the row can have the more recent date of the snapshot for ordering
+        CURRENT_TIMESTAMP() as snapshot_date,
+        total_transaction_amount,
+    -- saved, reusable sql operations can be performed with dbt macros
+        {{ get_account_status('last_transaction_date', 'last_payment_date') 
+            }} as account_status,
+
+    from
+        account_transactions
+)
+
+select * from final
+{% endsnapshot %}
+
+
+-- macros are saved in files like macros/account_management_macros
+-- a macro is defined with the variables it's expecting
+{% macro get_account_status(last_transaction_date, last_payment_date) %}
+-- the sql saved for a macro will be performed on the given fields
+case
+    when {{ last_transaction_date }} < {{last_payment_date}} and 
+        last_payment_date < CURRENT_DATE - INTERVAL '1 year' then 'Dormant'
+    when {{ last_transaction_date }} > {{last_payment_date}} - INTERVAL 
+        '90 days' then 'Overdue'
+    else 'Active'
+end
+-- % endmacro marks the end of the macro code block
+{% endmacro %}
+
+```
+
+## Configurations
+
+```yml
+#########################################################
+# dbt_project.yml
+#########################################################
+#
+# cli commands are executed in same working directory as dbt_project.yml
+# dbt_project.yml will always have following values 
+name: organization_project_name        
+version: "1.0"                           
+profile:  database_profile
+
+# And many optional values with implicit defaults
+# like folder locations
+model-paths: ["models"]
+# or the output of the model 
+models:
+  organization_project:
+    +materialized: view     # Default materialization for models
+    # these configurations are hierarchical and will act as defaults for files 
+    # without config blocks
+
+#########################################################
+# profiles.yml
+#########################################################
+# The profile specified in dbt_project.yml is defined within `profiles.yml`
+database_profile:
+# Like all dbt files it can contain hard coded values
+  target: hardcoded_target_environment_name
+  outputs:
+    dev:
+        type: postgres
+# or environment variables using jinja
+        user: "{{ env_var('POSTGRES_USER') }}"
+        password: "{{ env_var('POSTGRES_PW') }}"
+    # with defaults for variables if not available
+        database: "{{ env_var('POSTGRES_DB', 'core') }}"
+    # and python augmentation of variables
+        schema: "{{ '_'.join([env_var('POSTGRES_USER').replace('.', '_').upper()
+        , env_var('POSTGRES_SCHEMA') ]) }}"
+        role: "{{ env_var('POSTGRES_ROLE')}}"
+```
+
+### CLI Commands
+
+```bash
+# cli commands are executed in same working directory as dbt_project.yml
+
+# .csv files are seeded into database
+dbt seed
+# .sql or .py models are materialized in the database as tables or view
+dbt run
+# .sql or .yml tests can be performed
+dbt test
+# models can be materialized, ran, and shapshotted
+dbt build
+# a command can specify a model
+dbt build --select final_model
+    # with upstream dependencies
+dbt build --select +final_model
+    # and / or downstream dependencies
+dbt build --select +final_model+
+# metadata can be generated on materialized models
+dbt docs generate
+# full command list available in
+dbt list
+```
+
+### Repository Structure
+
+```text
+dbt has a default file structure when configurations do not define location
+
+repository/
+└── dbt/
+    ├── dbt_project.yml                        # Required
+    ├── profiles.yml                           # Required 
+    ├── models/                                # Required , optional name
+    │   ├── staging/                           # Optional subfolders
+    │   |   └── staging_model.sql
+    │   └── final_model.sql
+    ├── macros/                                # Optional macro functions
+    │   └── custom_macros.sql
+    ├── snapshots/                             # Optional snapshot models
+    │   └── snapshot.sql
+    ├── seeds/                                 # Optional csv files
+    │   └── seed_data.csv
+    ├── logs/                                  # Output location
+    ├── target/                                # Output location
+    └── tests/                                 # Optional model tests
+        └── custom_tests.sql
+```
+
+## Further Reading
+
+* [dbt logging](https://docs.getdbt.com/reference/global-configs/logs) - dbt documentation on outputs logs that can capture execution &
+debug logging
+* [dbt metadata artifacts](https://docs.getdbt.com/reference/artifacts/dbt-artifacts) - dbt documentation on generated artifacts, such as
+json documents for detailing attributes & metadata of a project