Feature/safe divide (dbt-labs#697)

* add safe_divide documentation

* add safe_divide macro

* add integration test for safe_divide macro

* moved macro and documentation to new SQL generator section

Co-authored-by: Grace Goheen <graciegoheen@gmail.com>

README.md

@@ -45,6 +45,7 @@ Check [dbt Hub](https://hub.getdbt.com/dbt-labs/dbt_utils/latest/) for the lates
   - [generate_series](#generate_series-source)
   - [surrogate_key](#surrogate_key-source)
   - [safe_add](#safe_add-source)
+  - [safe_divide](#safe_divide-source)
   - [pivot](#pivot-source)
   - [unpivot](#unpivot-source)
   - [width_bucket](#width_bucket-source)
@@ -1024,6 +1025,21 @@ Implements a cross-database way to sum nullable fields using the fields specifie
 {{ dbt_utils.safe_add('field_a', 'field_b'[,...]) }}
 ```
 
+#### safe_divide ([source](macros/cross_db_utils/safe_divide.sql))
+
+This macro performs division but returns null if the denominator is 0. 
+
+**Args:**
+
+- `numerator` (required): The number you want to divide.
+- `denominator` (required): The number you want to divide by.
+
+**Usage:**
+
+```
+{{ dbt_utils.safe_divide('numerator', 'denominator') }}
+```
+
 #### pivot ([source](macros/sql/pivot.sql))
 
 This macro pivots values from rows to columns.

integration_tests/data/sql/data_safe_divide.csv

@@ -0,0 +1,9 @@
+numerator,denominator,output
+6,0,
+10,5,2
+,,
+,0,
+17,,
+0,,
+,9,
+0,5,0

integration_tests/models/sql/schema.yml

@@ -91,6 +91,12 @@ models:
           actual: actual
           expected: expected
 
+  - name: test_safe_divide
+    tests:
+      - assert_equal:
+          actual: actual
+          expected: expected
+
   - name: test_pivot
     tests:
       - dbt_utils.equality:

integration_tests/models/sql/test_safe_divide.sql

@@ -0,0 +1,12 @@
+
+with data as (
+
+    select * from {{ ref('data_safe_divide') }}
+
+)
+
+select
+    {{ dbt_utils.safe_divide('numerator', 'denominator') }} as actual,
+    output as expected
+
+from data

macros/sql/safe_divide.sql

@@ -0,0 +1,7 @@
+{% macro safe_divide(numerator, denominator) -%}
+  {{ return(adapter.dispatch('safe_divide', 'dbt_utils')(numerator, denominator)) }}
+{%- endmacro %}
+
+{% macro default__safe_divide(numerator, denominator) %}
+    {{ numerator }} / nullif( {{ denominator }}, 0)
+{% endmacro %}