Setting a variable to CAST(NULL as X) set the result type of the variable to X. (Bug #6598)

mysql-test/r/bigint.result:
  Test to show show that the parser threats big longlong values as unsigned
mysql-test/r/user_var.result:
  Test of CAST(NULL as SIGNED/UNSIGNED)
mysql-test/t/bigint.test:
  Test to show show that the parser threats big longlong values as unsigned
mysql-test/t/user_var.test:
  Test of CAST(NULL as SIGNED/UNSIGNED)
sql/item_func.cc:
  Setting a variable to CAST(NULL as X) set the result type of the variable to X. (Bug #6598)
  Setting a variable to NULL doesn't change the old result type.
sql/item_func.h:
  Detect setting a variable to NULL
sql/unireg.cc:
  Safety fix

1 files changed, 26 insertions, 0 deletions

diff --git a/mysql-test/t/user_var.test b/mysql-test/t/user_var.test
index ef360f2231d..b9d06558f34 100644
--- a/mysql-test/t/user_var.test
+++ b/mysql-test/t/user_var.test
@@ -119,3 +119,29 @@ select coercibility(@v1),coercibility(@v2),coercibility(@v3),coercibility(@v4);
 set session @honk=99;
 --error 1382
 set one_shot @honk=99;
+
+#
+# Bug #6598: problem with cast(NULL as signed integer);
+#
+
+set @first_var= NULL;
+create table t1 select @first_var;
+show create table t1;
+drop table t1;
+set @first_var= cast(NULL as signed integer);
+create table t1 select @first_var;
+show create table t1;
+drop table t1;
+set @first_var= NULL;
+create table t1 select @first_var;
+show create table t1;
+drop table t1;
+set @first_var= concat(NULL);
+create table t1 select @first_var;
+show create table t1;
+drop table t1;
+set @first_var=1;
+set @first_var= cast(NULL as CHAR);
+create table t1 select @first_var;
+show create table t1;
+drop table t1;