executor: cleanup entries from mysql.db on revoke (#38370)

close #38363

executor/revoke.go

@@ -242,6 +242,17 @@ func (e *RevokeExec) revokeDBPriv(internalSession sessionctx.Context, priv *ast.
 	}
 	sqlexec.MustFormatSQL(sql, " WHERE User=%? AND Host=%? AND DB=%?", userName, host, dbName)
 
+	_, err = internalSession.(sqlexec.SQLExecutor).ExecuteInternal(ctx, sql.String())
+	if err != nil {
+		return err
+	}
+
+	sql = new(strings.Builder)
+	sqlexec.MustFormatSQL(sql, "DELETE FROM %n.%n WHERE User=%? AND Host=%? AND DB=%?", mysql.SystemDB, mysql.DBTable, userName, host, dbName)
+
+	for _, v := range append(mysql.AllDBPrivs, mysql.GrantPriv) {
+		sqlexec.MustFormatSQL(sql, " AND %n='N'", v.ColumnString())
+	}
 	_, err = internalSession.(sqlexec.SQLExecutor).ExecuteInternal(ctx, sql.String())
 	return err
 }

executor/revoke_test.go

@@ -72,7 +72,13 @@ func TestRevokeDBScope(t *testing.T) {
 
 		tk.MustQuery(check).Check(testkit.Rows("Y"))
 		tk.MustExec(sql)
-		tk.MustQuery(check).Check(testkit.Rows("N"))
+		if v == mysql.AllDBPrivs[len(mysql.AllDBPrivs)-1] {
+			// When all privileges are set to 'N', then the record should be removed as well.
+			// https://github.com/pingcap/tidb/issues/38363
+			tk.MustQuery(check).Check(testkit.Rows())
+		} else {
+			tk.MustQuery(check).Check(testkit.Rows("N"))
+		}
 	}
 }