Bug#35497623: SHOW INDEXES with generated column may access wrong key-part

In SHOW INDEXES we iterate over the KEY_PART_INFOs
of a KEY, and if it's a functional index, we try
to show its gcol_info (as in, "generated column info").

Unfortunately in the unpatched server, we try to obtain
that gcol_info from the first key-part in the key,
rather than from the current key-part.

This patch rectifies this.

While we're at it, we also make Column_name NULLable,
seeing as we occasionally set it to NULL (as we do in
the test case added by this patch). This aligns the
result of SHOW INDEXES for temporary tables with that
of regular tables.

Change-Id: I021c905150e38cd84739e5f4f69494781fb3d88e

Author: Tatiana Azundris Nuernberg

mysql-test/r/functional_index.result

@@ -158,13 +158,13 @@ DROP TABLE t1;
 CREATE TABLE t1 (col1 INT, INDEX ((ABS(col1))));
 DROP TABLE t1;
 # Print out functional indexes on a temporary table. Note that
-# "Column_name" should be empty (NULL), and Expression should contain the
+# "Column_name" should be NULL, and Expression should contain the
 # expression for the functional index.
 CREATE TEMPORARY TABLE t1(a INT);
 CREATE INDEX idx ON t1 ((ABS(a)));
 SHOW KEYS FROM t1;
 Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment	Visible	Expression
-t1	1	idx	1		A	0	NULL	NULL	YES	BTREE			YES	abs(`a`)
+t1	1	idx	1	NULL	A	0	NULL	NULL	YES	BTREE			YES	abs(`a`)
 DROP TABLE t1;
 CREATE TABLE t1 (col1 INT, INDEX ((CONCAT(''))));
 ERROR HY000: The used storage engine cannot index the expression 'concat(_utf8mb4'')'.
@@ -776,3 +776,31 @@ INDEX i1((FIND_IN_SET('Admin', roles)))
 
 # Clean up.
 DROP TABLE t1;
+
+#
+# Bug#35497623: SHOW INDEXES with generated column may access wrong key-part
+#
+
+# SHOW INDEXES on regular table:
+CREATE TABLE t1 (c1 INT);
+CREATE TABLE t2
+(UNIQUE i3 TYPE BTREE (c1, (c1 REGEXP c1))) TABLE t1;
+SHOW INDEXES IN t2;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment	Visible	Expression
+t2	0	i3	1	c1	A	0	NULL	NULL	YES	BTREE			YES	NULL
+t2	0	i3	2	NULL	A	0	NULL	NULL	YES	BTREE			YES	regexp_like(`c1`,`c1`)
+/* regular table */
+DROP TABLE t2;
+DROP TABLE t1;
+
+# SHOW INDEXES on temporary table (different code path!):
+CREATE TABLE t1 (c1 INT);
+CREATE TEMPORARY TABLE t2
+(UNIQUE i3 TYPE BTREE (c1, (c1 REGEXP c1))) TABLE t1;
+SHOW INDEXES IN t2;
+Table	Non_unique	Key_name	Seq_in_index	Column_name	Collation	Cardinality	Sub_part	Packed	Null	Index_type	Comment	Index_comment	Visible	Expression
+t2	0	i3	1	c1	A	0	NULL	NULL	YES	BTREE			YES	NULL
+t2	0	i3	2	NULL	A	0	NULL	NULL	YES	BTREE			YES	regexp_like(`c1`,`c1`)
+/* temporary table */
+DROP TABLE t2;
+DROP TABLE t1;

mysql-test/t/functional_index.test

@@ -137,7 +137,7 @@ CREATE TABLE t1 (col1 INT, INDEX ((ABS(col1))));
 DROP TABLE t1;
 
 --echo # Print out functional indexes on a temporary table. Note that
---echo # "Column_name" should be empty (NULL), and Expression should contain the
+--echo # "Column_name" should be NULL, and Expression should contain the
 --echo # expression for the functional index.
 CREATE TEMPORARY TABLE t1(a INT);
 CREATE INDEX idx ON t1 ((ABS(a)));
@@ -678,7 +678,29 @@ CREATE TABLE t1 (
   INDEX i1((FIND_IN_SET('Admin', roles)))
 );
 
-
 --echo
 --echo # Clean up.
 DROP TABLE t1;
+
+--echo
+--echo #
+--echo # Bug#35497623: SHOW INDEXES with generated column may access wrong key-part
+--echo #
+
+--echo
+--echo # SHOW INDEXES on regular table:
+CREATE TABLE t1 (c1 INT);
+CREATE TABLE t2
+             (UNIQUE i3 TYPE BTREE (c1, (c1 REGEXP c1))) TABLE t1;
+SHOW INDEXES IN t2; /* regular table */
+DROP TABLE t2;
+DROP TABLE t1;
+
+--echo
+--echo # SHOW INDEXES on temporary table (different code path!):
+CREATE TABLE t1 (c1 INT);
+CREATE TEMPORARY TABLE t2
+       (UNIQUE i3 TYPE BTREE (c1, (c1 REGEXP c1))) TABLE t1;
+SHOW INDEXES IN t2; /* temporary table */
+DROP TABLE t2;
+DROP TABLE t1;

sql/sql_show.cc

@@ -4397,7 +4397,7 @@ static int get_schema_tmp_table_keys_record(THD *thd, Table_ref *tables,
       // Expression for functional key parts
       if (key_part->field != nullptr &&
           key_part->field->is_field_for_functional_index()) {
-        Value_generator *gcol = key_info->key_part->field->gcol_info;
+        Value_generator *gcol = key_part->field->gcol_info;
 
         table->field[TMP_TABLE_KEYS_EXPRESSION]->store(
             gcol->expr_str.str, gcol->expr_str.length, cs);
@@ -4965,7 +4965,7 @@ ST_FIELD_INFO tmp_table_keys_fields_info[] = {
     {"INDEX_SCHEMA", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, nullptr, 0},
     {"INDEX_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, "Key_name", 0},
     {"SEQ_IN_INDEX", 2, MYSQL_TYPE_LONGLONG, 0, 0, "Seq_in_index", 0},
-    {"COLUMN_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 0, "Column_name", 0},
+    {"COLUMN_NAME", NAME_CHAR_LEN, MYSQL_TYPE_STRING, 0, 1, "Column_name", 0},
     {"COLLATION", 1, MYSQL_TYPE_STRING, 0, 1, "Collation", 0},
     {"CARDINALITY", MY_INT64_NUM_DECIMAL_DIGITS, MYSQL_TYPE_LONGLONG, 0, 1,
      "Cardinality", 0},