allow SELECT; and column name for cast result fix

Author: jennifersp

postgres/parser/parser/sql.y

@@ -10685,6 +10685,12 @@ empty_select:
       Window:  $7.window(),
     }
   }
+| SELECT
+  {
+    $$.val = &tree.SelectClause{
+      Exprs:   make(tree.SelectExprs, 0, 0),
+    }
+  }
 
 // %Help: SELECT - retrieve rows from a data source and compute a result
 // %Category: DML
@@ -10747,7 +10753,6 @@ simple_select_clause:
       Window:     $9.window(),
     }
   }
-| SELECT error // SHOW HELP: SELECT
 
 opt_join_hint_comment:
   {

server/ast/select.go

@@ -133,9 +133,30 @@ func nodeSelectExpr(ctx *Context, node tree.SelectExpr) (vitess.SelectExpr, erro
 		if err != nil {
 			return nil, err
 		}
-		// cast part is not part of column name, e.g. `id::INT2` should create column name as `id`.
+
 		if ce, ok := expr.(*tree.CastExpr); ok && node.As == "" {
-			node.As = tree.UnrestrictedName(tree.AsString(ce.Expr))
+			hasConst := false
+			_, _ = tree.SimpleVisit(expr, func(visitingExpr tree.Expr) (recurse bool, newExpr tree.Expr, err error) {
+				switch visitingExpr.(type) {
+				case tree.Constant:
+					hasConst = true
+					return false, visitingExpr, nil
+				}
+				return true, visitingExpr, nil
+			})
+			if hasConst {
+				_, dt, err := nodeResolvableTypeReference(ctx, ce.Type, false)
+				if err != nil {
+					return nil, err
+				}
+				// constant value is not part of column name
+				// e.g. `1::INT2` should create column name as `int2`.
+				node.As = tree.UnrestrictedName(dt.Name())
+			} else {
+				// cast type is not part of column name
+				// e.g. `id::INT2` should create column name as `id`.
+				node.As = tree.UnrestrictedName(tree.AsString(ce.Expr))
+			}
 		}
 
 		return &vitess.AliasedExpr{

testing/go/select_test.go

@@ -23,6 +23,15 @@ import (
 // TestSelect covers SELECT syntax not covered by our MySQL select tests
 func TestSelect(t *testing.T) {
 	RunScripts(t, []ScriptTest{
+		{
+			Name: "SELECT empty",
+			Assertions: []ScriptTestAssertion{
+				{
+					Query:    "SELECT;",
+					Expected: []sql.Row{nil},
+				},
+			},
+		},
 		{
 			Name: "SELECT DISTINCT ON",
 			SetUpScript: []string{

testing/go/types_test.go

@@ -41,8 +41,9 @@ var typesTests = []ScriptTest{
 				},
 			},
 			{
-				Query:    `SELECT 1::pg_catalog.int8;`,
-				Expected: []sql.Row{{1}},
+				Query:            `SELECT 1::pg_catalog.int8;`,
+				ExpectedColNames: []string{"int8"},
+				Expected:         []sql.Row{{1}},
 			},
 		},
 	},
@@ -415,13 +416,15 @@ var typesTests = []ScriptTest{
 				},
 			},
 			{
-				Query: "SELECT '!'::bpchar;",
+				Query:            "SELECT '!'::bpchar;",
+				ExpectedColNames: []string{"bpchar"},
 				Expected: []sql.Row{
 					{"!"},
 				},
 			},
 			{
-				Query: "SELECT '!'::bpchar(1);",
+				Query:            "SELECT '!'::bpchar(1);",
+				ExpectedColNames: []string{"bpchar"},
 				Expected: []sql.Row{
 					{"!"},
 				},
@@ -547,7 +550,8 @@ var typesTests = []ScriptTest{
 				},
 			},
 			{
-				Query: `SELECT 'def'::name::"char";`,
+				Query:            `SELECT 'def'::name::"char";`,
+				ExpectedColNames: []string{"char"},
 				Expected: []sql.Row{
 					{"d"},
 				},
@@ -799,7 +803,8 @@ var typesTests = []ScriptTest{
 				},
 			},
 			{
-				Query: "SELECT date '2022-02-02'",
+				Query:            "SELECT date '2022-02-02'",
+				ExpectedColNames: []string{"date"},
 				Expected: []sql.Row{
 					{"2022-02-02"},
 				},
@@ -3669,6 +3674,16 @@ var enumTypeTests = []ScriptTest{
 				Query:    `INSERT INTO person VALUES ('Moe', 'happy'), ('Larry', 'sad'), ('Curly', 'ok');`,
 				Expected: []sql.Row{},
 			},
+			{
+				Query:            `SELECT 'happy'::mood;`,
+				ExpectedColNames: []string{"mood"},
+				Expected:         []sql.Row{{"happy"}},
+			},
+			{
+				Query:            `SELECT current_mood::mood from person where name = 'Moe';`,
+				ExpectedColNames: []string{"current_mood"},
+				Expected:         []sql.Row{{"happy"}},
+			},
 			{
 				Query:    `SELECT * FROM person order by current_mood;`,
 				Expected: []sql.Row{{"Larry", "sad"}, {"Curly", "ok"}, {"Moe", "happy"}},