sql: ignore empty statements during Prepare

Fixes #9093
Fixes #9518

GLOCKFILE

@@ -65,7 +65,7 @@ github.com/kkaneda/returncheck bf081fa7155e3a27df1f056a49d50685edfa5b1b
 github.com/kr/pretty cfb55aafdaf3ec08f0db22699ab822c50091b1c4
 github.com/kr/text 7cafcd837844e784b526369c9bce262804aebc60
 github.com/leekchan/timeutil 28917288c48df3d2c1cfe468c273e0b2adda0aa5
-github.com/lib/pq 50761b0867bd1d9d069276790bcd4a3bccf2324a
+github.com/lib/pq fcb9ef54da7cae1ea08f0b5a92f236d83e59294a
 github.com/lightstep/lightstep-tracer-go 7ec5005048fddb1fc15627e1bf58796ce01d919e
 github.com/mattn/go-isatty 66b8e73f3f5cda9f96b69efd03dd3d7fc4a5cdb8
 github.com/mattn/go-runewidth d6bea18f789704b5f83375793155289da36a3c7f

sql/executor.go

@@ -340,10 +340,20 @@ func (e *Executor) Prepare(
 	if traceSQL {
 		log.Eventf(session.Ctx(), "preparing: %s", query)
 	}
-	stmt, err := parser.ParseOne(query, parser.Syntax(session.Syntax))
+	var p parser.Parser
+	stmts, err := p.Parse(query, parser.Syntax(session.Syntax))
 	if err != nil {
 		return nil, err
 	}
+	switch len(stmts) {
+	case 0:
+		return nil, nil
+	case 1:
+		// ignore
+	default:
+		return nil, errors.Errorf("expected 1 statement, but found %d", len(stmts))
+	}
+	stmt := stmts[0]
 	if err = pinfo.ProcessPlaceholderAnnotations(stmt); err != nil {
 		return nil, err
 	}

sql/pgwire_test.go

@@ -660,9 +660,10 @@ CREATE TABLE d.str (s STRING, b BYTES);`
 }
 
 type preparedExecTest struct {
-	qargs        []interface{}
-	rowsAffected int64
-	error        string
+	qargs           []interface{}
+	rowsAffected    int64
+	error           string
+	rowsAffectedErr bool
 }
 
 func (p preparedExecTest) SetArgs(v ...interface{}) preparedExecTest {
@@ -680,6 +681,11 @@ func (p preparedExecTest) Error(err string) preparedExecTest {
 	return p
 }
 
+func (p preparedExecTest) RowsAffectedErr() preparedExecTest {
+	p.rowsAffectedErr = true
+	return p
+}
+
 func TestPGPreparedExec(t *testing.T) {
 	defer leaktest.AfterTest(t)()
 	var baseTest preparedExecTest
@@ -797,6 +803,28 @@ func TestPGPreparedExec(t *testing.T) {
 				baseTest,
 			},
 		},
+		// An empty string is valid in postgres.
+		{
+			"",
+			[]preparedExecTest{
+				baseTest.RowsAffectedErr(),
+			},
+		},
+		// Empty statements are permitted.
+		{
+			";",
+			[]preparedExecTest{
+				baseTest.RowsAffectedErr(),
+			},
+		},
+		// Any number of empty statements are permitted with a single statement
+		// anywhere.
+		{
+			"; ; SET DATABASE = system; ;",
+			[]preparedExecTest{
+				baseTest,
+			},
+		},
 	}
 
 	s, _, _ := serverutils.StartServer(t, base.TestServerArgs{})
@@ -823,8 +851,10 @@ func TestPGPreparedExec(t *testing.T) {
 					t.Errorf("%s: %v: expected error: %s, got %s", query, test.qargs, test.error, err)
 				}
 			} else {
-				if rowsAffected, err := result.RowsAffected(); err != nil {
-					t.Errorf("%s: %v: unexpected error: %s", query, test.qargs, err)
+				rowsAffected, err := result.RowsAffected()
+				hasRAErr := err != nil
+				if hasRAErr != test.rowsAffectedErr {
+					t.Errorf("%s: expected rows affected error: %v, got %v (error %+v)", query, test.rowsAffectedErr, hasRAErr, err)
 				} else if rowsAffected != test.rowsAffected {
 					t.Errorf("%s: %v: expected %v, got %v", query, test.qargs, test.rowsAffected, rowsAffected)
 				}
@@ -939,11 +969,13 @@ func TestCmdCompleteVsEmptyStatements(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	defer func() {
-		_ = recover()
-	}()
-	_, _ = empty.RowsAffected() // should panic if lib/pq returned a nil result as expected.
-	t.Fatal("should not get here -- empty result from empty query should panic first")
+	rows, err := empty.RowsAffected()
+	if rows != 0 {
+		t.Fatalf("expected 0 rows, got %d", rows)
+	}
+	if err == nil {
+		t.Fatal("expected error")
+	}
 }
 
 // Unfortunately lib/pq doesn't expose returned command tags directly, but we can test