opt/optbuilder: support using table name as projection

* Fix projection code to be able to use the column name as a table name
  by catching undefined columns error and evaluating it as a TupleStar
* Fix scope VisitPre to do something similar to above, to make this work
  for functions.

Release note (sql change): Using the table name as a projection now
works, e.g. SELECT table_name FROM table_name or SELECT
row_to_json(table_name) FROM table_name.

pkg/sql/logictest/testdata/logic_test/tuple

@@ -914,10 +914,23 @@ a  b
 1  one
 2  two
 
-
-# Pending #26719
-query error pq: column "t" does not exist
+query I rowsort
 SELECT (t).a FROM t
+----
+1
+2
+
+query T rowsort
+SELECT t FROM t
+----
+(1,one)
+(2,two)
+
+query T rowsort
+SELECT row_to_json(t) FROM t
+----
+{"a": 1, "b": "one"}
+{"a": 2, "b": "two"}
 
 statement ok
 DROP TABLE t

pkg/sql/opt/optbuilder/project.go

@@ -16,6 +16,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode"
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgerror"
 	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
+	"github.com/cockroachdb/cockroach/pkg/sql/sqlerrors"
 	"github.com/cockroachdb/cockroach/pkg/sql/types"
 )
 
@@ -186,9 +187,17 @@ func (b *Builder) resolveColRef(e tree.Expr, inScope *scope) tree.TypedExpr {
 	unresolved, ok := e.(*tree.UnresolvedName)
 	if ok && !unresolved.Star && unresolved.NumParts == 1 {
 		colName := unresolved.Parts[0]
-		_, srcMeta, _, err := inScope.FindSourceProvidingColumn(b.ctx, tree.Name(colName))
-		if err != nil {
-			panic(err)
+		_, srcMeta, _, resolveErr := inScope.FindSourceProvidingColumn(b.ctx, tree.Name(colName))
+		if resolveErr != nil {
+			if sqlerrors.IsUndefinedColumnError(resolveErr) {
+				// It may be a reference to a table, e.g. SELECT tbl FROM tbl.
+				// Attempt to resolve as a TupleStar.
+				return func() tree.TypedExpr {
+					defer wrapColTupleStarPanic(resolveErr)
+					return inScope.resolveType(columnNameAsTupleStar(colName), types.Any)
+				}()
+			}
+			panic(resolveErr)
 		}
 		return srcMeta.(tree.TypedExpr)
 	}

pkg/sql/opt/optbuilder/scope.go

@@ -925,9 +925,17 @@ func (s *scope) VisitPre(expr tree.Expr) (recurse bool, newExpr tree.Expr) {
 		return s.VisitPre(vn)
 
 	case *tree.ColumnItem:
-		colI, err := t.Resolve(s.builder.ctx, s)
-		if err != nil {
-			panic(err)
+		colI, resolveErr := t.Resolve(s.builder.ctx, s)
+		if resolveErr != nil {
+			if sqlerrors.IsUndefinedColumnError(resolveErr) {
+				// Attempt to resolve as columnname.*, which allows items
+				// such as SELECT row_to_json(tbl_name) FROM tbl_name to work.
+				return func() (bool, tree.Expr) {
+					defer wrapColTupleStarPanic(resolveErr)
+					return s.VisitPre(columnNameAsTupleStar(string(t.ColumnName)))
+				}()
+			}
+			panic(resolveErr)
 		}
 		return false, colI.(*scopeColumn)
 
@@ -1593,3 +1601,27 @@ func (s *scope) String() string {
 
 	return buf.String()
 }
+
+func columnNameAsTupleStar(colName string) *tree.TupleStar {
+	return &tree.TupleStar{
+		Expr: &tree.UnresolvedName{
+			Star:     true,
+			NumParts: 2,
+			Parts:    tree.NameParts{"", colName},
+		},
+	}
+}
+
+// wrapColTupleStarPanic checks for panics and if the pgcode is
+// UndefinedTable panics with the originalError.
+// Otherwise, it will panic with the recovered error.
+func wrapColTupleStarPanic(originalError error) {
+	if r := recover(); r != nil {
+		if err, ok := r.(error); ok {
+			if sqlerrors.IsUndefinedRelationError(err) {
+				panic(originalError)
+			}
+		}
+		panic(r)
+	}
+}

pkg/sql/opt/optbuilder/testdata/select

@@ -234,6 +234,31 @@ project
  └── scan kv
       └── columns: k:1!null v:2 crdb_internal_mvcc_timestamp:3
 
+build
+SELECT row_to_json(kv) FROM kv
+----
+project
+ ├── columns: row_to_json:4
+ ├── scan kv
+ │    └── columns: k:1!null v:2 crdb_internal_mvcc_timestamp:3
+ └── projections
+      └── row_to_json(((k:1, v:2) AS k, v)) [as=row_to_json:4]
+
+build
+SELECT kv FROM kv
+----
+project
+ ├── columns: kv:4
+ ├── scan kv
+ │    └── columns: k:1!null v:2 crdb_internal_mvcc_timestamp:3
+ └── projections
+      └── ((k:1, v:2) AS k, v) [as=kv:4]
+
+build
+SELECT log(kv) FROM kv
+----
+error (42883): unknown signature: log(tuple{char AS k, char AS v})
+
 build
 SELECT (kv.*) AS r FROM kv
 ----
@@ -1478,3 +1503,40 @@ build
 DELETE FROM inaccessible RETURNING v
 ----
 error (42703): column "v" does not exist
+
+exec-ddl
+CREATE TABLE same_name (
+  same_name TEXT PRIMARY KEY,
+  b INT
+)
+----
+
+build
+SELECT same_name FROM same_name
+----
+project
+ ├── columns: same_name:1!null
+ └── scan same_name
+      └── columns: same_name:1!null b:2 crdb_internal_mvcc_timestamp:3
+
+build
+SELECT row_to_json(same_name) FROM same_name
+----
+error (42883): unknown signature: row_to_json(string)
+
+build
+SELECT log(same_name) FROM same_name
+----
+error (42883): unknown signature: log(string)
+
+build
+SELECT t FROM (VALUES (1,2), (3,4)) t(x, y);
+----
+project
+ ├── columns: t:3!null
+ ├── values
+ │    ├── columns: column1:1!null column2:2!null
+ │    ├── (1, 2)
+ │    └── (3, 4)
+ └── projections
+      └── ((column1:1, column2:2) AS x, y) [as=t:3]