Enhance usability of star macro by only generating column aliases whe…

…n prefix and/or suffix is specified (#468)

* The star macro should only produce column aliases when there is either a prefix or suffix specified.

* Enhanced the readme for the star macro.

* Add new integration test

Co-authored-by: Nick Perrott <nperrott@roiti.com>
Co-authored-by: Josh Elston-Green
Co-authored-by: Joel Labes <joel.labes@dbtlabs.com>

README.md

@@ -729,7 +729,9 @@ group by 1,2,3
 ```
 
 #### star ([source](macros/sql/star.sql))
-This macro generates a list of all fields that exist in the `from` relation, excluding any fields listed in the `except` argument. The construction is identical to `select * from {{ref('my_model')}}`, replacing star (`*`) with the star macro. This macro also has an optional `relation_alias` argument that will prefix all generated fields with an alias (`relation_alias`.`field_name`). The macro also has optional `prefix` and `suffix` arguments, which will be appropriately concatenated to each field name in the output (`prefix` ~ `field_name` ~ `suffix`).
+This macro generates a comma-separated list of all fields that exist in the `from` relation, excluding any fields listed in the `except` argument. The construction is identical to `select * from {{ref('my_model')}}`, replacing star (`*`) with the star macro. This macro also has an optional `relation_alias` argument that will prefix all generated fields with an alias (`relation_alias`.`field_name`). 
+
+The macro also has optional `prefix` and `suffix` arguments. When one or both are provided, they will be concatenated onto each field's alias in the output (`prefix` ~ `field_name` ~ `suffix`). NB: This prevents the output from being used in any context other than a select statement.
 
 **Usage:**
 ```sql

integration_tests/data/sql/data_star_aggregate.csv

@@ -0,0 +1,5 @@
+group_field_1,group_field_2,value_field
+a,b,1
+a,b,2
+c,d,3
+c,e,4

integration_tests/data/sql/data_star_aggregate_expected.csv

@@ -0,0 +1,4 @@
+group_field_1,group_field_2,value_field_sum
+a,b,3
+c,d,3
+c,e,4

integration_tests/models/sql/schema.yml

@@ -111,6 +111,11 @@ models:
       - dbt_utils.equality:
           compare_model: ref('data_star_prefix_suffix_expected')
 
+  - name: test_star_aggregate
+    tests:
+      - dbt_utils.equality:
+          compare_model: ref('data_star_aggregate_expected')
+
   - name: test_surrogate_key
     tests:
       - assert_equal:

integration_tests/models/sql/test_star_aggregate.sql

@@ -0,0 +1,16 @@
+{#-/*This test checks that column aliases aren't applied unless there's a prefix/suffix necessary, to ensure that GROUP BYs keep working*/-#}
+
+{% set selected_columns = dbt_utils.star(from=ref('data_star_aggregate'), except=['value_field']) %}
+
+with data as (
+
+    select
+        {{ selected_columns }},
+        sum(value_field) as value_field_sum
+
+    from {{ ref('data_star_aggregate') }}
+    group by {{ selected_columns }}
+
+)
+
+select * from data

macros/sql/star.sql

@@ -24,7 +24,7 @@
 
     {%- for col in include_cols %}
 
-        {%- if relation_alias %}{{ relation_alias }}.{% else %}{%- endif -%}{{ adapter.quote(col)|trim }} as {{ adapter.quote(prefix ~ col ~ suffix)|trim }}
+        {%- if relation_alias %}{{ relation_alias }}.{% else %}{%- endif -%}{{ adapter.quote(col)|trim }} {%- if prefix!='' or suffix!='' -%} as {{ adapter.quote(prefix ~ col ~ suffix)|trim }} {%- endif -%}
         {%- if not loop.last %},{{ '\n  ' }}{% endif %}
 
     {%- endfor -%}