18 files declare their use of DatabaseException in Drupal 9

BatchStorage.php in core/lib/Drupal/Core/Batch/BatchStorage.php

Connection.php in core/lib/Drupal/Core/Database/Driver/mysql/Connection.php

DatabaseBackend.php in core/lib/Drupal/Core/Flood/DatabaseBackend.php

DatabaseBackend.php in core/lib/Drupal/Core/Cache/DatabaseBackend.php

DatabaseCacheTagsChecksum.php in core/lib/Drupal/Core/Cache/DatabaseCacheTagsChecksum.php

DatabaseLockBackend.php in core/lib/Drupal/Core/Lock/DatabaseLockBackend.php

DatabaseQueue.php in core/lib/Drupal/Core/Queue/DatabaseQueue.php

DatabaseStorage.php in core/lib/Drupal/Core/Config/DatabaseStorage.php

DbLog.php in core/modules/dblog/src/Logger/DbLog.php

FieldsOverlapException.php in core/lib/Drupal/Core/Database/Query/FieldsOverlapException.php

InstallerRedirectTrait.php in core/lib/Drupal/Core/Installer/InstallerRedirectTrait.php

InvalidMergeQueryException.php in core/lib/Drupal/Core/Database/Query/InvalidMergeQueryException.php

LargeQueryTest.php in core/tests/Drupal/KernelTests/Core/Database/LargeQueryTest.php

MatcherDumper.php in core/lib/Drupal/Core/Routing/MatcherDumper.php

MenuTreeStorage.php in core/lib/Drupal/Core/Menu/MenuTreeStorage.php

NoFieldsException.php in core/lib/Drupal/Core/Database/Query/NoFieldsException.php

NoUniqueFieldException.php in core/lib/Drupal/Core/Database/Query/NoUniqueFieldException.php

Sql.php in core/modules/migrate/src/Plugin/migrate/id_map/Sql.php