fix for bug #1946:

"You can always mysql_real_query a query with placeholders 
after mysql_prepare()"

sql/sql_class.cc

@@ -90,8 +90,8 @@ THD::THD():user_time(0), is_fatal_error(0),
 {
   host=user=priv_user=db=query=ip=0;
   host_or_ip= "connecting host";
-  locked=killed=some_tables_deleted=no_errors=password=
-    query_start_used=prepare_command=0;
+  locked=killed=some_tables_deleted=no_errors=password= 0;
+  query_start_used= 0;
   count_cuted_fields= CHECK_FIELD_IGNORE;
   db_length=query_length=col_access=0;
   query_error= tmp_table_used= 0;

sql/sql_class.h

@@ -606,7 +606,6 @@ public:
   bool	     system_thread,in_lock_tables,global_read_lock;
   bool       query_error, bootstrap, cleanup_done;
   bool	     volatile killed;
-  bool       prepare_command;
   bool	     tmp_table_used;
   bool	     charset_is_system_charset, charset_is_collation_connection;
   bool       slow_command;

sql/sql_prepare.cc

@@ -785,7 +785,6 @@ static bool parse_prepare_query(PREP_STMT *stmt,
   mysql_init_query(thd);   
   LEX *lex=lex_start(thd, (uchar*) packet, length);
   lex->safe_to_cache_query= 0;
-  thd->prepare_command= TRUE; 
   thd->lex.param_count= 0;
   if (!yyparse((void *)thd) && !thd->is_fatal_error) 
     error= send_prepare_results(stmt);

sql/sql_yacc.yy

@@ -4355,7 +4355,7 @@ param_marker:
         '?'
         {
 	  LEX *lex=Lex;
-          if (YYTHD->prepare_command)
+          if (YYTHD->command == COM_PREPARE)
           {
             lex->param_list.push_back($$=new Item_param((uint)(lex->tok_start-(uchar *)YYTHD->query)));
             lex->param_count++;

tests/client_test.c

@@ -8065,6 +8065,32 @@ static void test_bug1500()
   mysql_stmt_close(stmt);
 }
 
+static void test_bug1946()
+{
+  MYSQL_STMT *stmt;
+  int rc;
+
+  myheader("test_bug1946");
+  const char *query= "INSERT INTO prepare_command VALUES (?)";
+  
+  rc = mysql_query(mysql, "DROP TABLE IF EXISTS prepare_command");
+  myquery(rc);
+  
+  rc= mysql_query(mysql,"CREATE TABLE prepare_command(ID INT)");
+  myquery(rc);
+
+  stmt = mysql_prepare(mysql, query, strlen(query));
+  mystmt_init(stmt);
+  rc= mysql_real_query(mysql, query, strlen(query));
+  assert(rc != 0);
+  fprintf(stdout, "Got error (as expected):\n");
+  myerror(NULL);
+
+  mysql_stmt_close(stmt);
+  rc= mysql_query(mysql,"DROP TABLE prepare_command");
+}
+
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */
@@ -8208,6 +8234,8 @@ int main(int argc, char **argv)
     /* Used for internal new development debugging */
     test_drop_temp();       /* to test DROP TEMPORARY TABLE Access checks */
 #endif
+    test_bug1946(); /* test that placeholders are allowed only in 
+                               prepared queries */
     test_fetch_seek();      /* to test stmt seek() functions */
     test_fetch_nobuffs();   /* to fecth without prior bound buffers */
     test_open_direct();     /* direct execution in the middle of open stmts */