Fix show warnings limit 0 and show warnings limit 0, 0.

Add test coverage for SHOW WARNINGS LIMIT a, b;

mysql-test/r/warnings.result

@@ -179,3 +179,56 @@ drop table t1;
 set table_type=MYISAM;
 Warnings:
 Warning	1287	'table_type' is deprecated; use 'storage_engine' instead
+create table t1 (a int);
+insert into t1 (a) values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);
+update t1 set a='abc';
+Warnings:
+Warning	1265	Data truncated for column 'a' at row 1
+Warning	1265	Data truncated for column 'a' at row 2
+Warning	1265	Data truncated for column 'a' at row 3
+Warning	1265	Data truncated for column 'a' at row 4
+Warning	1265	Data truncated for column 'a' at row 5
+Warning	1265	Data truncated for column 'a' at row 6
+Warning	1265	Data truncated for column 'a' at row 7
+Warning	1265	Data truncated for column 'a' at row 8
+Warning	1265	Data truncated for column 'a' at row 9
+Warning	1265	Data truncated for column 'a' at row 10
+show warnings limit 2, 1;
+Level	Code	Message
+Warning	1265	Data truncated for column 'a' at row 3
+show warnings limit 0, 10;
+Level	Code	Message
+Warning	1265	Data truncated for column 'a' at row 1
+Warning	1265	Data truncated for column 'a' at row 2
+Warning	1265	Data truncated for column 'a' at row 3
+Warning	1265	Data truncated for column 'a' at row 4
+Warning	1265	Data truncated for column 'a' at row 5
+Warning	1265	Data truncated for column 'a' at row 6
+Warning	1265	Data truncated for column 'a' at row 7
+Warning	1265	Data truncated for column 'a' at row 8
+Warning	1265	Data truncated for column 'a' at row 9
+Warning	1265	Data truncated for column 'a' at row 10
+show warnings limit 9, 1;
+Level	Code	Message
+Warning	1265	Data truncated for column 'a' at row 10
+show warnings limit 10, 1;
+Level	Code	Message
+show warnings limit 9, 2;
+Level	Code	Message
+Warning	1265	Data truncated for column 'a' at row 10
+show warnings limit 0, 0;
+Level	Code	Message
+show warnings limit 1;
+Level	Code	Message
+Warning	1265	Data truncated for column 'a' at row 1
+show warnings limit 0;
+Level	Code	Message
+show warnings limit 1, 0;
+Level	Code	Message
+select * from t1 limit 0;
+a
+select * from t1 limit 1, 0;
+a
+select * from t1 limit 0, 0;
+a
+drop table t1;

mysql-test/t/warnings.test

@@ -133,3 +133,25 @@ drop table t1;
 # Test for deprecated table_type variable
 #
 set table_type=MYISAM;
+
+#
+# Tests for show warnings limit a, b
+#
+create table t1 (a int);
+insert into t1 (a) values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);
+# should generate 10 warnings
+update t1 set a='abc';
+show warnings limit 2, 1;
+show warnings limit 0, 10;
+show warnings limit 9, 1;
+show warnings limit 10, 1;
+show warnings limit 9, 2;
+show warnings limit 0, 0;
+show warnings limit 1;
+show warnings limit 0;
+show warnings limit 1, 0;
+# make sure behaviour is consistent with select ... limit
+select * from t1 limit 0;
+select * from t1 limit 1, 0;
+select * from t1 limit 0, 0;
+drop table t1;

sql/sql_error.cc

@@ -203,6 +203,8 @@ my_bool mysqld_show_warnings(THD *thd, ulong levels_to_show)
       offset--;
       continue;
     }
+    if (limit-- == 0)
+      break;
     protocol->prepare_for_resend();
     protocol->store(warning_level_names[err->level],
 		    warning_level_length[err->level], system_charset_info);
@@ -210,8 +212,6 @@ my_bool mysqld_show_warnings(THD *thd, ulong levels_to_show)
     protocol->store(err->msg, strlen(err->msg), system_charset_info);
     if (protocol->write())
       DBUG_RETURN(1);
-    if (!--limit)
-      break;
   }
   send_eof(thd);  
   DBUG_RETURN(0);