I'm migrating a MYSQL DB from one host to another so I run the following command to backup the DB from the old hosting:
mysqldump -u **** -p **** | gzip > /home/***/***.sql.gz
zcat /home/***/***.sql.gz | mysql -u *** -p ***
If you look at the output of mysqldump (before you gzip it) you will see that it contains a sequence of
DROP TABLE x; CREATE TABLE x (...); INSERT INTO x (...) VALUES (...);
So, no, it does not do an insert / replace, it drops and recreates the tables.