select.result, select.test:

  Added a test case for bug #5333.
null_key.result, key_primary.result:
  Made covering index usable for const tables.
sql_select.cc:
  Made covering index usable for const tables:
  downported the corresponding code from 4.1.
  Simultaneously fixed bug #5333 reported for 4.1.
  The bug was due to the fact that field index in join
  structures was always set to 0 for const tables.


sql/sql_select.cc:
  Made covering index usable for const tables:
  downported the corresponding code from 4.1.
  Simultaneously fixed bug #5333 reported for 4.1.
  The bug was due to the fact that field index in join
  structures was always set to 0 for const tables.
mysql-test/t/select.test:
  Added a test case for bug #5333.
mysql-test/r/key_primary.result:
  Made covering index usable for const tables.
mysql-test/r/null_key.result:
  Made covering index usable for const tables.
mysql-test/r/select.result:
  Added a test case for bug #5333.

5 files changed, 49 insertions, 3 deletions

diff --git a/mysql-test/r/key_primary.result b/mysql-test/r/key_primary.result
index 87289f1cf54..3216ead667b 100644
--- a/mysql-test/r/key_primary.result
+++ b/mysql-test/r/key_primary.result
@@ -13,7 +13,7 @@ t1
 AB%
 describe select * from t1 where t1="ABC";
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	const	PRIMARY	PRIMARY	3	const	1	
+t1	const	PRIMARY	PRIMARY	3	const	1	Using index
 describe select * from t1 where t1="ABCD";
 Comment
 Impossible WHERE noticed after reading const tables
diff --git a/mysql-test/r/null_key.result b/mysql-test/r/null_key.result
index 009a3e06eb2..41b0ae26617 100644
--- a/mysql-test/r/null_key.result
+++ b/mysql-test/r/null_key.result
@@ -12,7 +12,7 @@ table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	ref	a,b	a	9	const,const	1	Using where; Using index
 explain select * from t1 where a=2 and b = 2;
 table	type	possible_keys	key	key_len	ref	rows	Extra
-t1	const	a,b	a	9	const,const	1	
+t1	const	a,b	a	9	const,const	1	Using index
 explain select * from t1 where a<=>b limit 2;
 table	type	possible_keys	key	key_len	ref	rows	Extra
 t1	index	NULL	a	9	NULL	12	Using where; Using index
diff --git a/mysql-test/r/select.result b/mysql-test/r/select.result
index 206fa507615..ce5ea94a08e 100644
--- a/mysql-test/r/select.result
+++ b/mysql-test/r/select.result
@@ -2327,3 +2327,19 @@ select * from t2,t3 where t2.s = t3.s;
 s	s
 two		two	
 drop table t1, t2, t3;
+CREATE TABLE t1 (
+i int(11) NOT NULL default '0',
+c char(10) NOT NULL default '',
+PRIMARY KEY  (i),
+UNIQUE KEY c (c)
+) TYPE=MyISAM;
+INSERT INTO t1 VALUES (1,'a');
+INSERT INTO t1 VALUES (2,'b');
+INSERT INTO t1 VALUES (3,'c');
+EXPLAIN SELECT i FROM t1 WHERE i=1;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	const	PRIMARY	PRIMARY	4	const	1	Using index
+EXPLAIN SELECT i FROM t1 WHERE i=1;
+table	type	possible_keys	key	key_len	ref	rows	Extra
+t1	const	PRIMARY	PRIMARY	4	const	1	Using index
+DROP TABLE t1;
diff --git a/mysql-test/t/select.test b/mysql-test/t/select.test
index 7cb157f194e..dae44159683 100644
--- a/mysql-test/t/select.test
+++ b/mysql-test/t/select.test
@@ -1874,3 +1874,24 @@ select * from t3 where s = 'one';
 select * from t1,t2 where t1.s = t2.s;
 select * from t2,t3 where t2.s = t3.s;
 drop table t1, t2, t3;
+
+#
+# Covering index is mentioned in EXPLAIN output for const tables (bug #5333)
+#
+
+CREATE TABLE t1 (
+  i int(11) NOT NULL default '0',
+  c char(10) NOT NULL default '',
+  PRIMARY KEY  (i),
+  UNIQUE KEY c (c)
+) TYPE=MyISAM;
+
+INSERT INTO t1 VALUES (1,'a');
+INSERT INTO t1 VALUES (2,'b');
+INSERT INTO t1 VALUES (3,'c');
+
+EXPLAIN SELECT i FROM t1 WHERE i=1;
+
+EXPLAIN SELECT i FROM t1 WHERE i=1;
+
+DROP TABLE t1;
\ No newline at end of file
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 882f345a1ca..d2b9f9d4588 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -4901,6 +4901,15 @@ join_read_const_table(JOIN_TAB *tab, POSITION *pos)
   }
   else
   {
+    if (!table->key_read &&
+        (table->used_keys & ((key_map) 1 << tab->ref.key)) &&
+    	!table->no_keyread &&
+        (int) table->reginfo.lock_type <= (int) TL_READ_HIGH_PRIORITY)
+    {
+      table->key_read=1;
+      table->file->extra(HA_EXTRA_KEYREAD);
+      tab->index= tab->ref.key;
+    }
     if ((error=join_read_const(tab)))
     {
       tab->info="unique row not found";
@@ -7617,7 +7626,7 @@ static void select_describe(JOIN *join, bool need_tmp_table, bool need_order,
       sprintf(buff3,"%.0f",join->best_positions[i].records_read);
       item_list.push_back(new Item_string(buff3,strlen(buff3)));
       my_bool key_read=table->key_read;
-      if (tab->type == JT_NEXT &&
+      if ((tab->type == JT_NEXT || tab->type == JT_CONST) &&
 	  ((table->used_keys & ((key_map) 1 << tab->index))))
 	key_read=1;