Extensions to support this:

SHOW CREATE DATABASE [IF NOT EXISTS] dbname

Version dependant parts are displayed in appropriative comments:
CREATE DATABASE /*!32312 IF NOT EXISTS*/ `ucs` /*!40100 DEFAULT CHARACTER SET ucs2*/


client/mysqldump.c:
  SHOW CREATE DATABASE IF NOT EXISTS
sql/mysql_priv.h:
  SHOW CREATE DATABASE IF NOT EXISTS
sql/sql_db.cc:
  SHOW CREATE DATABASE IF NOT EXISTS
sql/sql_parse.cc:
  SHOW CREATE DATABASE IF NOT EXISTS
sql/sql_yacc.yy:
  SHOW CREATE DATABASE IF NOT EXISTS

client/mysqldump.c

@@ -1252,7 +1252,7 @@ static int init_dumping(char *database)
         MYSQL_ROW row;
         MYSQL_RES *dbinfo;
 	
-        sprintf(qbuf,"SHOW CREATE DATABASE %s",database);
+        sprintf(qbuf,"SHOW CREATE DATABASE IF NOT EXISTS %s",database);
         
         if (mysql_query(sock, qbuf) || !(dbinfo = mysql_store_result(sock)))
         {

sql/mysql_priv.h

@@ -496,7 +496,7 @@ int mysqld_show_logs(THD *thd);
 void mysqld_list_fields(THD *thd,TABLE_LIST *table, const char *wild);
 int mysqld_dump_create_info(THD *thd, TABLE *table, int fd = -1);
 int mysqld_show_create(THD *thd, TABLE_LIST *table_list);
-int mysqld_show_create_db(THD *thd, const char *dbname);
+int mysqld_show_create_db(THD *thd, const char *dbname, HA_CREATE_INFO *create);
 
 void mysqld_list_processes(THD *thd,const char *user,bool verbose);
 int mysqld_show_status(THD *thd);

sql/sql_db.cc

@@ -597,7 +597,7 @@ bool mysql_change_db(THD *thd, const char *name)
 }
 
 
-int mysqld_show_create_db(THD *thd, const char *dbname)
+int mysqld_show_create_db(THD *thd, const char *dbname, HA_CREATE_INFO *create_info)
 {
   int length;
   char	path[FN_REFLEN], *to;
@@ -605,6 +605,8 @@ int mysqld_show_create_db(THD *thd, const char *dbname)
   bool found_libchar;
   HA_CREATE_INFO create;
   CONVERT *convert=thd->variables.convert_set;
+  uint create_options = create_info ? create_info->options : 0;
+  
   DBUG_ENTER("mysql_show_create_db");
   
   if (check_db_name(dbname))
@@ -660,12 +662,17 @@ int mysqld_show_create_db(THD *thd, const char *dbname)
   String *packet = &thd->packet;
   packet->length(0);
   net_store_data(packet, convert, dbname);
-  to= strxmov(path, "CREATE DATABASE `", dbname, "`", NullS);
+  to= strxmov(path, "CREATE DATABASE ", NullS);
+  if (create_options & HA_LEX_CREATE_IF_NOT_EXISTS)
+    to= strxmov(to,"/*!32312 IF NOT EXISTS*/ ", NullS);
+  to=strxmov(to,"`",dbname,"`", NullS);
+  
   if (create.table_charset)
-    to= strxmov(to," DEFAULT CHARACTER SET ", create.table_charset->name,
-		NullS);
+    to= strxmov(to," /*!40100 DEFAULT CHARACTER SET ", 
+		create.table_charset->name,"*/",NullS);
+  
   net_store_data(packet, convert, path, (uint) (to-path));
-
+  
   if (my_net_write(&thd->net,(char*) packet->ptr(), packet->length()))
     DBUG_RETURN(1);
   

sql/sql_parse.cc

@@ -2462,7 +2462,7 @@ mysql_execute_command(THD *thd)
       send_error(thd,ER_LOCK_OR_ACTIVE_TRANSACTION);
       goto error;
     }
-    res=mysqld_show_create_db(thd,lex->name);
+    res=mysqld_show_create_db(thd,lex->name,&lex->create_info);
     break;
   }
   case SQLCOM_CREATE_FUNCTION:

sql/sql_yacc.yy

@@ -2987,7 +2987,13 @@ opt_table_sym:
  
 /* Show things */
 
-show:	SHOW { Lex->wild=0;} show_param;
+show:	SHOW 
+	{ 
+	  LEX *lex=Lex;
+	  lex->wild=0;
+	  bzero((char*) &lex->create_info,sizeof(lex->create_info));
+	}
+	show_param;
 
 show_param:
 	DATABASES wild
@@ -3100,10 +3106,11 @@ show_param:
 	    lex->grant_user=$3;
 	    lex->grant_user->password.str=NullS;
 	  }
-	| CREATE DATABASE ident
+	| CREATE DATABASE opt_if_not_exists ident
 	  {
 	    Lex->sql_command=SQLCOM_SHOW_CREATE_DB;
-	    Lex->name=$3.str;
+	    Lex->create_info.options=$3;
+	    Lex->name=$4.str;
 	  }
         | CREATE TABLE_SYM table_ident
           {