mysql (5.5.) cmd unresponsive when selecting a huge db
The client message should read (emphasis mine)


  Reading table information for completion of table and column names You
  can turn off this feature to get a quicker startup with -A


where "-A" is the shortcut for --no-auto-rehash.

By Default, the MySQL client will, on connection, run queries on the INFORMATION_SCHEMA to discover


all the tables in the current database
all the columns for all the tables found


This is to support "auto completion", so that a human can type

SELECT * FROM EMPLO&lt;TAB&gt;


and the tool will then expand the query text to

SELECT * FROM EMPLOYEE


This feature is very costly when the database is big, and it should be disabled to improve connection time.

See the reference manual:
https://dev.mysql.com/doc/refman/5.7/en/mysql-command-options.html#option_mysql_auto-rehash