Inline limit in SQL sent from dbt show (#8641)

.changes/unreleased/Fixes-20230913-153924.yaml

@@ -0,0 +1,6 @@
+kind: Fixes
+body: 'update dbt show to include limit in DWH query '
+time: 2023-09-13T15:39:24.591805+01:00
+custom:
+  Author: michelleark
+  Issue: 8496, 8417

core/dbt/include/global_project/macros/adapters/show.sql

@@ -0,0 +1,24 @@
+{% macro get_show_sql(compiled_code, sql_header, limit) -%}
+  {%- set sql_header = sql_header -%}
+  {{ sql_header if sql_header is not none }}
+  {%- if sql_header -%}
+  {{ sql_header }}
+  {%- endif -%}
+  {%- if limit is not none -%}
+  {{ get_limit_subquery_sql(compiled_code, limit) }}
+  {%- else -%}
+  {{ compiled_code }}
+  {%- endif -%}
+{% endmacro %}
+
+{% macro get_limit_subquery_sql(sql, limit) %}
+  {{ adapter.dispatch('get_limit_subquery_sql', 'dbt')(sql, limit) }}
+{% endmacro %}
+
+{% macro default__get_limit_subquery_sql(sql, limit) %}
+    select *
+    from (
+        {{ sql }}
+    ) as model_limit_subq
+    limit {{ limit }}
+{% endmacro %}

core/dbt/task/show.py

@@ -2,6 +2,7 @@
 import threading
 import time
 
+from dbt.context.providers import generate_runtime_model_context
 from dbt.contracts.graph.nodes import SeedNode
 from dbt.contracts.results import RunResult, RunStatus
 from dbt.events.base_types import EventLevel
@@ -20,14 +21,24 @@ def __init__(self, config, adapter, node, node_index, num_nodes):
     def execute(self, compiled_node, manifest):
         start_time = time.time()
 
-        if "sql_header" in compiled_node.unrendered_config:
-            compiled_node.compiled_code = (
-                compiled_node.unrendered_config["sql_header"] + compiled_node.compiled_code
-            )
-
+        # Allow passing in -1 (or any negative number) to get all rows
+        limit = None if self.config.args.limit < 0 else self.config.args.limit
+
+        model_context = generate_runtime_model_context(compiled_node, self.config, manifest)
+        compiled_node.compiled_code = self.adapter.execute_macro(
+            macro_name="get_show_sql",
+            manifest=manifest,
+            context_override=model_context,
+            kwargs={
+                "compiled_code": model_context["compiled_code"],
+                "sql_header": model_context["config"].get("sql_header"),
+                "limit": limit,
+            },
+        )
         adapter_response, execute_result = self.adapter.execute(
             compiled_node.compiled_code, fetch=True
         )
+
         end_time = time.time()
 
         return RunResult(

tests/adapter/dbt/tests/adapter/dbt_show/fixtures.py

@@ -0,0 +1,34 @@
+models__sql_header = """
+{% call set_sql_header(config) %}
+set session time zone '{{ var("timezone", "Europe/Paris") }}';
+{%- endcall %}
+select current_setting('timezone') as timezone
+"""
+
+models__ephemeral_model = """
+{{ config(materialized = 'ephemeral') }}
+select
+    coalesce(sample_num, 0) + 10 as col_deci
+from {{ ref('sample_model') }}
+"""
+
+models__second_ephemeral_model = """
+{{ config(materialized = 'ephemeral') }}
+select
+    col_deci + 100 as col_hundo
+from {{ ref('ephemeral_model') }}
+"""
+
+models__sample_model = """
+select * from {{ ref('sample_seed') }}
+"""
+
+seeds__sample_seed = """sample_num,sample_bool
+1,true
+2,false
+3,true
+4,false
+5,true
+6,false
+7,true
+"""

tests/adapter/dbt/tests/adapter/dbt_show/test_dbt_show.py

@@ -0,0 +1,62 @@
+import pytest
+from dbt.tests.util import run_dbt
+
+from dbt.tests.adapter.dbt_show.fixtures import (
+    models__sql_header,
+    models__ephemeral_model,
+    models__second_ephemeral_model,
+    models__sample_model,
+    seeds__sample_seed,
+)
+
+
+# -- Below we define base classes for tests you import based on if your adapter supports dbt show or not --
+class BaseShowLimit:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "sample_model.sql": models__sample_model,
+            "ephemeral_model.sql": models__ephemeral_model,
+        }
+
+    @pytest.fixture(scope="class")
+    def seeds(self):
+        return {"sample_seed.csv": seeds__sample_seed}
+
+    @pytest.mark.parametrize(
+        "args,expected",
+        [
+            ([], 5),  # default limit
+            (["--limit", 3], 3),  # fetch 3 rows
+            (["--limit", -1], 7),  # fetch all rows
+        ],
+    )
+    def test_limit(self, project, args, expected):
+        run_dbt(["build"])
+        dbt_args = ["show", "--inline", models__second_ephemeral_model, *args]
+        results = run_dbt(dbt_args)
+        assert len(results.results[0].agate_table) == expected
+        # ensure limit was injected in compiled_code when limit specified in command args
+        limit = results.args.get("limit")
+        if limit > 0:
+            assert f"limit {limit}" in results.results[0].node.compiled_code
+
+
+class BaseShowSqlHeader:
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "sql_header.sql": models__sql_header,
+        }
+
+    def test_sql_header(self, project):
+        run_dbt(["build", "--vars", "timezone: Asia/Kolkata"])
+        run_dbt(["show", "--select", "sql_header", "--vars", "timezone: Asia/Kolkata"])
+
+
+class TestPostgresShowSqlHeader(BaseShowSqlHeader):
+    pass
+
+
+class TestPostgresShowLimit(BaseShowLimit):
+    pass

tests/functional/show/fixtures.py

@@ -12,7 +12,7 @@
 
 models__sql_header = """
 {% call set_sql_header(config) %}
-set session time zone 'Asia/Kolkata';
+set session time zone '{{ var("timezone", "Europe/Paris") }}';
 {%- endcall %}
 select current_setting('timezone') as timezone
 """

tests/functional/show/test_show.py

@@ -9,7 +9,6 @@
     models__second_model,
     models__ephemeral_model,
     schema_yml,
-    models__sql_header,
     private_model_yml,
 )
 
@@ -21,7 +20,6 @@ def models(self):
             "sample_model.sql": models__sample_model,
             "second_model.sql": models__second_model,
             "ephemeral_model.sql": models__ephemeral_model,
-            "sql_header.sql": models__sql_header,
         }
 
     @pytest.fixture(scope="class")
@@ -88,15 +86,6 @@ def test_second_ephemeral_model(self, project):
         )
         assert "col_hundo" in log_output
 
-    def test_seed(self, project):
-        (results, log_output) = run_dbt_and_capture(["show", "--select", "sample_seed"])
-        assert "Previewing node 'sample_seed'" in log_output
-
-    def test_sql_header(self, project):
-        run_dbt(["build"])
-        (results, log_output) = run_dbt_and_capture(["show", "--select", "sql_header"])
-        assert "Asia/Kolkata" in log_output
-
 
 class TestShowModelVersions:
     @pytest.fixture(scope="class")