MySQL compatibility: BLOB vs TEXT for String types

[slvrtrn]

Describe the issue
All the string types are reported as BLOB if use_mysql_types_in_show_columns is set to 1. This, unfortunately, causes issues with QuickSight via MySQL interface, as it cannot recognize BLOB columns as strings. For example:

As you can see, BLOB (aka LONGVARBINARY, see the explanation) does not work here as expected. However, this works fine with tools such as Looker Studio.

How to reproduce

• Which ClickHouse server version to use: the latest master build
• Which interface to use, if matters: MySQL
• Non-default settings, if any: users.xml -> add <use_mysql_types_in_show_columns>1</use_mysql_types_in_show_columns> to the default profile.
• Sample data: commits sample dataset
• Queries to run:

show full columns from commits;

Preferred solution
While BLOB is technically the correct type for representing Strings via MySQL interface, a configuration option to switch between BLOB and TEXT globally reported types for String columns in the SHOW (FULL) COLUMNS output will enable us to integrate with QuickSight better.

CC @rschu1ze

[EugeniyPetrov]

Related #52777