Fixes bug #14569. When no db is selected as current and we do create procedure db.sp()...

we changing current db temporarily and restore it when sp is created. however thd->db
in this case becomes empty string rather than NULL and so all checks of thd->db == NULL 
will be false. So if after this we'll issue create procedure sp2()... without specifying
db it will succeed and create sp with db=NULL, which causes mysqldto crash on 
show procedure status statement.

This patch fixes the problem.

1 files changed, 11 insertions, 2 deletions

diff --git a/sql/sql_db.cc b/sql/sql_db.cc
index a5dabc8140c..bde6522a38b 100644
--- a/sql/sql_db.cc
+++ b/sql/sql_db.cc
@@ -1163,8 +1163,17 @@ bool mysql_change_db(THD *thd, const char *name, bool no_access_check)
   }
 end:
   x_free(thd->db);
-  thd->db=dbname;				// THD::~THD will free this
-  thd->db_length=db_length;
+  if (dbname && dbname[0] == 0)
+  {
+    x_free(dbname);
+    thd->db= NULL;
+    thd->db_length= 0;
+  }
+  else
+  {
+    thd->db= dbname;				// THD::~THD will free this
+    thd->db_length= db_length;
+  }
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
   if (!no_access_check)
     sctx->db_access= db_access;