fix for SQL_CALC_FOUND_ROWS in UNION's

Docs/manual.texi

@@ -48946,6 +48946,10 @@ Our TODO section contains what we plan to have in 4.0. @xref{TODO MySQL 4.0}.
 
 @itemize @bullet
 @item
+fixed that SQL_CALC_FOUND_ROWS works with UNIONs. It will work only if first 
+select has this option and if there is global LIMIT for entire select. For the
+moment this requires using braces for individual select's.
+@item
 Don't give an error for @code{CREATE TABLE ...(... VARCHAR(0))}.
 @item
 Fixed @code{SIGINT} and @code{SIGQUIT} problems in @file{mysql.cc} on Linux

mysql-test/r/union.result

@@ -89,6 +89,13 @@ table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	NULL	NULL	NULL	NULL	4	
 t2	ALL	NULL	NULL	NULL	NULL	4	Using filesort
 t1	ALL	NULL	NULL	NULL	NULL	4	
+(select sql_calc_found_rows  a,b from t1 limit 2)  union all (select a,b from t2 order by a) limit 2;
+a	b
+1	a
+2	b
+select found_rows();
+FOUND_ROWS()
+6
 explain select a,b from t1 union all select a,b from t2;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ALL	NULL	NULL	NULL	NULL	4	

mysql-test/t/union.test

@@ -21,7 +21,8 @@ select 't1',b,count(*) from t1 group by b UNION select 't2',b,count(*) from t2 g
 (select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1);
 (select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1) order by b desc;
 explain (select a,b from t1 limit 2)  union all (select a,b from t2 order by a limit 1) order by b desc;
-
+(select sql_calc_found_rows  a,b from t1 limit 2)  union all (select a,b from t2 order by a) limit 2;
+select found_rows();
 # Test some error conditions with UNION
 explain select a,b from t1 union all select a,b from t2;
 

sql/sql_union.cc

@@ -33,6 +33,7 @@ int mysql_union(THD *thd, LEX *lex,select_result *result)
   TABLE *table;
   int describe=(lex->select_lex.options & SELECT_DESCRIBE) ? 1 : 0;
   int res;
+  bool fr=false;
   TABLE_LIST result_table_list;
   TABLE_LIST *first_table=(TABLE_LIST *)lex->select_lex.table_list.first;
   TMP_TABLE_PARAM tmp_table_param;
@@ -60,6 +61,7 @@ int mysql_union(THD *thd, LEX *lex,select_result *result)
     */
     lex_sl= sl;
     order=  (ORDER *) lex_sl->order_list.first;
+    fr = lex->select_lex.options & OPTION_FOUND_ROWS && !describe && sl->select_limit && sl->select_limit != HA_POS_ERROR;
     if (!order || !describe) 
       last_sl->next=0;				// Remove this extra element
   }
@@ -198,6 +200,8 @@ int mysql_union(THD *thd, LEX *lex,select_result *result)
 		       item_list, NULL, (describe) ? 0 : order,
 		       (ORDER*) NULL, NULL, (ORDER*) NULL,
 		       thd->options, result);
+      if (fr && !res)
+	thd->limit_found_rows = (ulonglong)table->file->records;
     }
   }