first pass: add limit in show sql

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

@@ -0,0 +1,21 @@
+{% macro show(limit) -%}
+  {%- set sql_header = config.get('sql_header', none) -%}
+  {{ sql_header if sql_header is not none }}
+  {%- 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
@@ -23,14 +24,15 @@ def execute(self, compiled_node, manifest):
         # 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
 
-        if "sql_header" in compiled_node.unrendered_config:
-            compiled_node.compiled_code = (
-                compiled_node.unrendered_config["sql_header"] + compiled_node.compiled_code
-            )
-
-        adapter_response, execute_result = self.adapter.execute(
-            compiled_node.compiled_code, fetch=True, limit=limit
+        model_context = generate_runtime_model_context(compiled_node, self.config, manifest)
+        show_limit_sql = self.adapter.execute_macro(
+            macro_name="show",
+            manifest=manifest,
+            context_override=model_context,
+            kwargs={"limit": limit},
         )
+        adapter_response, execute_result = self.adapter.execute(show_limit_sql, fetch=True)
+
         end_time = time.time()
 
         return RunResult(