sql: add SHOW CREATE FUNCTION support

Release note (sql change): This commit adds support for the
SHOW CREATE FUNCTION statement. If given function name is
qualified, the explicit schema will be searched. If function
name is not qualified, the schemas on search path are searched
and functions from the most significant schema are returned.

pkg/sql/crdb_internal.go

@@ -2629,7 +2629,6 @@ CREATE TABLE crdb_internal.create_function_statements (
 				)
 			})
 		})
-		return nil
 	},
 }
 

pkg/sql/delegate/show_function.go

@@ -11,10 +11,42 @@
 package delegate
 
 import (
+	"fmt"
+
+	"github.com/cockroachdb/cockroach/pkg/sql/lexbase"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
-	"github.com/cockroachdb/cockroach/pkg/util/errorutil/unimplemented"
+	"github.com/cockroachdb/errors"
 )
 
 func (d *delegator) delegateShowCreateFunction(n *tree.ShowCreateFunction) (tree.Statement, error) {
-	return nil, unimplemented.New("SHOW CREATE FUNCTION", "this statement is not yet supported")
+	// We don't need to filter by db since we don't allow cross-database
+	// references.
+	query := `
+SELECT function_name, create_statement
+FROM crdb_internal.create_function_statements
+WHERE schema_name = %[1]s
+AND function_name = %[2]s
+`
+	un, ok := n.Name.FunctionReference.(*tree.UnresolvedName)
+	if !ok {
+		return nil, errors.AssertionFailedf("not a valid function name")
+	}
+
+	fn, err := d.catalog.ResolveFunction(d.ctx, un, &d.evalCtx.SessionData().SearchPath)
+	if err != nil {
+		return nil, err
+	}
+
+	var udfSchema string
+	for _, o := range fn.Overloads {
+		if o.IsUDF {
+			udfSchema = o.Schema
+		}
+	}
+	if udfSchema == "" {
+		return nil, errors.Errorf("function %s does not exist", tree.AsString(un))
+	}
+
+	fullQuery := fmt.Sprintf(query, lexbase.EscapeSQLString(udfSchema), lexbase.EscapeSQLString(un.Parts[0]))
+	return parse(fullQuery)
 }

pkg/sql/logictest/testdata/logic_test/show_create

@@ -140,8 +140,3 @@ CREATE TABLE public.t (
   CONSTRAINT t_pkey PRIMARY KEY (rowid ASC)
 );
 COMMENT ON COLUMN public.t.c IS 'first comment'
-
-subtest show_create_function
-
-statement error this statement is not yet supported
-SHOW CREATE FUNCTION lower

pkg/sql/logictest/testdata/logic_test/udf

@@ -333,54 +333,58 @@ $$  104  test  118  sc  119  proc_f_2
 
 subtest show_create_function
 
-query TT
-SHOW CREATE FUNCTION proc_f;
+query T
+SELECT @2 FROM [SHOW CREATE FUNCTION proc_f];
 ----
-proc_f  CREATE FUNCTION public.proc_f(IN INT8)
-RETURNS INT8
-VOLATILE
-NOT LEAKPROOF
-CALLED ON NULL INPUT
-AS $$
-SELECT 1;
+CREATE FUNCTION public.proc_f(IN INT8)
+    RETURNS INT8
+    VOLATILE
+    NOT LEAKPROOF
+    CALLED ON NULL INPUT
+    LANGUAGE SQL
+    AS $$
+    SELECT 1;
 $$
-proc_f  CREATE FUNCTION public.proc_f(IN STRING, IN b INT8)
-RETURNS SETOF STRING
-IMMUTABLE
-LEAKPROOF
-STRICT
-AS $$
-SELECT 'hello';
+CREATE FUNCTION public.proc_f(IN STRING, IN b INT8)
+    RETURNS SETOF STRING
+    IMMUTABLE
+    LEAKPROOF
+    STRICT
+    LANGUAGE SQL
+    AS $$
+    SELECT 'hello';
 $$
 
 statement error pq: unknown function: proc_f_2()
 SHOW CREATE FUNCTION proc_f_2;
 
-query TT
-SHOW CREATE FUNCTION sc.proc_f_2;
+query T
+SELECT @2 FROM [SHOW CREATE FUNCTION sc.proc_f_2];
 ----
-proc_f_2  CREATE FUNCTION sc.proc_f_2(IN STRING)
-RETURNS STRING
-VOLATILE
-NOT LEAKPROOF
-CALLED ON NULL INPUT
-AS $$
-SELECT 'hello';
+CREATE FUNCTION sc.proc_f_2(IN STRING)
+    RETURNS STRING
+    VOLATILE
+    NOT LEAKPROOF
+    CALLED ON NULL INPUT
+    LANGUAGE SQL
+    AS $$
+    SELECT 'hello';
 $$
 
 statement ok
 SET search_path = sc;
 
-query TT
-SHOW CREATE FUNCTION proc_f_2;
+query T
+SELECT @2 FROM [SHOW CREATE FUNCTION proc_f_2];
 ----
-proc_f_2  CREATE FUNCTION sc.proc_f_2(IN STRING)
-RETURNS STRING
-VOLATILE
-NOT LEAKPROOF
-CALLED ON NULL INPUT
-AS $$
-SELECT 'hello';
+CREATE FUNCTION sc.proc_f_2(IN STRING)
+    RETURNS STRING
+    VOLATILE
+    NOT LEAKPROOF
+    CALLED ON NULL INPUT
+    LANGUAGE SQL
+    AS $$
+    SELECT 'hello';
 $$
 
 statement ok

pkg/sql/opt_catalog.go

@@ -331,13 +331,13 @@ func (oc *optCatalog) ResolveType(
 func (oc *optCatalog) ResolveFunction(
 	ctx context.Context, name *tree.UnresolvedName, path tree.SearchPath,
 ) (*tree.ResolvedFunctionDefinition, error) {
-	return nil, errors.AssertionFailedf("unimplemented")
+	return oc.planner.ResolveFunction(ctx, name, path)
 }
 
 func (oc *optCatalog) ResolveFunctionByOID(
 	ctx context.Context, oid oid.Oid,
 ) (*tree.Overload, error) {
-	return nil, errors.AssertionFailedf("unimplemented")
+	return oc.planner.ResolveFunctionByOID(ctx, oid)
 }
 
 func getDescFromCatalogObjectForPermissions(o cat.Object) (catalog.Descriptor, error) {