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The collation used by the default database. The server sets this variable whenever the default database changes. If there is no default database, the variable has the same value as collation_server . 

As of MySQL 8.0.18, setting the session value of this system variable is no longer a restricted operation. 

The global character_set_database  and collation_database  system variables are deprecated; expect them to be removed in a future version of MySQL. 

Assigning a value to the session character_set_database  and collation_database  system variables is deprecated and assignments produce a warning. Expect the session variables to become read-only (and assignments to produce an error) in a future version of MySQL in which it remains possible to access the session variables to determine the database character set and collation for the default database. 

## • collation_server 

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The server’s default collation. See Section 10.15, “Character Set Configuration” . 

## • completion_type 

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