fix sign expr bug

tools/deploy/mysql_test/test_suite/static_engine/r/mysql/expr_sign.result

@@ -896,3 +896,17 @@ select sign(1E-400) from dual;
 +--------------+
 |            0 |
 +--------------+
+
+##bug:
+drop table if exists t1;
+create table t1(c1 bit(64),c2 bit(64));
+insert into t1(c1) values(1);
+
+select sign(c1) from t1;
++----------+
+| sign(c1) |
++----------+
+|        1 |
++----------+
+
+drop table t1;

tools/deploy/mysql_test/test_suite/static_engine/t/expr_sign.test

@@ -147,3 +147,16 @@ select sign( cast(a2 as char(1024)) ) , sign( cast(a4 as char(1024)) ) from t2 f
 --echo #
 select sign(1E-300) from dual;
 select sign(1E-400) from dual;
+
+##bug:
+
+--disable_warnings
+drop table if exists t1;
+--enable_warnings
+
+create table t1(c1 bit(64),c2 bit(64));
+insert into t1(c1) values(1);
+
+select sign(c1) from t1;
+
+drop table t1;