Bug #11754461 CANNOT ALTER TABLE WHEN KEY PREFIX TOO LONG

The problem was that doing ALTER TABLE on a table which had a key
on a TEXT/BLOB column with a prefix longer than the maximum number
of characteres in this column (as per the character set), by mistake,
caused an error (Error 1170 - ER_BLOB_KEY_WITHOUT_LENGTH).

This bug not repeatable in 5.5.

This patch adds a regression test to alter_table.test and
contains no code changes.

mysql-test/r/alter_table.result

@@ -1383,3 +1383,11 @@ ALTER TABLE t1 CHANGE a id INT;
 affected rows: 0
 info: Records: 0  Duplicates: 0  Warnings: 0
 DROP TABLE t1;
+#
+# Bug#11754461 CANNOT ALTER TABLE WHEN KEY PREFIX TOO LONG
+#
+DROP DATABASE IF EXISTS db1;
+CREATE DATABASE db1 CHARACTER SET utf8;
+CREATE TABLE db1.t1 (bar TINYTEXT, KEY (bar(100)));
+ALTER TABLE db1.t1 ADD baz INT;
+DROP DATABASE db1;

mysql-test/t/alter_table.test

@@ -1144,3 +1144,18 @@ INSERT INTO t1 VALUES (1, 1), (2, 2);
 ALTER TABLE t1 CHANGE a id INT;
 --disable_info
 DROP TABLE t1;
+
+
+--echo #
+--echo # Bug#11754461 CANNOT ALTER TABLE WHEN KEY PREFIX TOO LONG
+--echo #
+
+--disable_warnings
+DROP DATABASE IF EXISTS db1;
+--enable_warnings
+
+CREATE DATABASE db1 CHARACTER SET utf8;
+CREATE TABLE db1.t1 (bar TINYTEXT, KEY (bar(100)));
+ALTER TABLE db1.t1 ADD baz INT;
+
+DROP DATABASE db1;