Fix panic with select database() in OLAP mode (#6200)

Signed-off-by: Adam Saponara <[email protected]>

go/vt/vtgate/executor.go

@@ -1100,6 +1100,11 @@ func (e *Executor) StreamExecute(ctx context.Context, method string, safeSession
 		return err
 	}
 
+	err = e.addNeededBindVars(plan.BindVarNeeds, bindVars, safeSession)
+	if err != nil {
+		return err
+	}
+
 	execStart := time.Now()
 	logStats.PlanTime = execStart.Sub(logStats.StartTime)
 

go/vt/vtgate/executor_test.go

@@ -2344,3 +2344,21 @@ func TestGenerateCharsetRows(t *testing.T) {
 		})
 	}
 }
+
+func TestOlapSelectDatabase(t *testing.T) {
+	executor, _, _, _ := createExecutorEnv()
+	executor.normalize = true
+
+	session := &vtgatepb.Session{Autocommit: true}
+
+	sql := `select database()`
+	target := querypb.Target{}
+	cbInvoked := false
+	cb := func(r *sqltypes.Result) error {
+		cbInvoked = true
+		return nil
+	}
+	err := executor.StreamExecute(context.Background(), "TestExecute", NewSafeSession(session), sql, nil, target, cb)
+	assert.NoError(t, err)
+	assert.True(t, cbInvoked)
+}