MDEV-11172: EXPLAIN shows non-sensical value for key_len with type=index

The issue happens when the secondary keys are extended with primary
key parts. Inside the function TABLE_SHARE::init_from_binary_frm_image()
adds the length bytes for the primary key key parts to the length of the
secondary key. This is not needed because when the extended keys are
used we recalculate the length for the used key parts.

Also removed TABLE_SHARE::total_key_length as it is not used in the code
Apporved-by: Monty <monty@mariadb.org>

mysql-test/r/innodb_ext_key.result

@@ -790,3 +790,19 @@ EXPLAIN
 }
 drop table t1;
 SET optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+#
+# MDEV-11172: EXPLAIN shows non-sensical value for key_len with type=index
+#
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+CREATE TABLE t2 (
+pk VARCHAR(50),
+a VARCHAR(20),
+KEY k1(a),
+PRIMARY KEY(pk)
+)ENGINE=INNODB;
+INSERT INTO t2 SELECT a,a FROM t1;
+EXPLAIN SELECT pk FROM t2 FORCE INDEX(k1);
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t2	index	NULL	k1	23	NULL	10	Using index
+DROP TABLE t1,t2;

mysql-test/t/innodb_ext_key.test

@@ -606,3 +606,22 @@ explain format= json
 select * from t1 force index(k1)  where f2 <= 5 and pk2 <=5 and pk1 = 'abc' and f1 <= '3';
 drop table t1;
 SET optimizer_use_condition_selectivity=@save_optimizer_use_condition_selectivity;
+
+--echo #
+--echo # MDEV-11172: EXPLAIN shows non-sensical value for key_len with type=index
+--echo #
+
+CREATE TABLE t1(a INT);
+INSERT INTO t1 VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+CREATE TABLE t2 (
+  pk VARCHAR(50),
+  a VARCHAR(20),
+  KEY k1(a),
+  PRIMARY KEY(pk)
+)ENGINE=INNODB;
+
+INSERT INTO t2 SELECT a,a FROM t1;
+EXPLAIN SELECT pk FROM t2 FORCE INDEX(k1);
+
+DROP TABLE t1,t2;

sql/structs.h

@@ -90,7 +90,7 @@ class engine_option_value;
 struct ha_index_option_struct;
 
 typedef struct st_key {
-  uint	key_length;			/* Tot length of key */
+  uint	key_length;			/* total length of user defined key parts  */
   ulong flags;                          /* dupp key and pack flags */
   uint	user_defined_key_parts;	   /* How many key_parts */
   uint	usable_key_parts; /* Should normally be = user_defined_key_parts */

sql/table.cc

@@ -2273,6 +2273,12 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
           key_part->null_bit= field->null_bit;
           key_part->store_length+=HA_KEY_NULL_LENGTH;
           keyinfo->flags|=HA_NULL_PART_KEY;
+
+          /*
+            This branch is executed only for user defined key parts of the
+            secondary indexes.
+          */
+          DBUG_ASSERT(i < keyinfo->user_defined_key_parts);
           keyinfo->key_length+= HA_KEY_NULL_LENGTH;
         }
         if (field->type() == MYSQL_TYPE_BLOB ||
@@ -2285,7 +2291,8 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
           else
             key_part->key_part_flag|= HA_VAR_LENGTH_PART;
           key_part->store_length+=HA_KEY_BLOB_LENGTH;
-          keyinfo->key_length+= HA_KEY_BLOB_LENGTH;
+          if (i < keyinfo->user_defined_key_parts)
+            keyinfo->key_length+= HA_KEY_BLOB_LENGTH;
         }
         if (field->type() == MYSQL_TYPE_BIT)
           key_part->key_part_flag|= HA_BIT_PART;
@@ -2378,7 +2385,6 @@ int TABLE_SHARE::init_from_binary_frm_image(THD *thd, bool write,
 
       set_if_bigger(share->max_key_length,keyinfo->key_length+
                     keyinfo->user_defined_key_parts);
-      share->total_key_length+= keyinfo->key_length;
       /*
         MERGE tables do not have unique indexes. But every key could be
         an unique index on the underlying MyISAM table. (Bug #10400)

sql/table.h

@@ -773,7 +773,7 @@ struct TABLE_SHARE
   uint rec_buff_length;                 /* Size of table->record[] buffer */
   uint keys, key_parts;
   uint ext_key_parts;       /* Total number of key parts in extended keys */
-  uint max_key_length, max_unique_length, total_key_length;
+  uint max_key_length, max_unique_length;
   uint uniques;                         /* Number of UNIQUE index */
   uint db_create_options;		/* Create options from database */
   uint db_options_in_use;		/* Options in use */