Checking if mysql user exists

When in need to check if a user exists without deleting it (for instance when just skipping some instructions instead of executing them in any case), one can use this (where $USER is the user to check):

if [ $(echo "SELECT COUNT(*) FROM mysql.user WHERE user = '$USER'" | mysql | tail -n1) -gt 0 ]
then
  echo "User exists"
else
  echo "User doesn't exist"
fi

NB:

• mysql command requires extra args and/or configuration for authentication)
• tail -n1 is used for removing the query result header

As newer versions of MySQL allow this option:

DROP USER IF EXISTS 'username'@'host';

MySQL stores user data in a table called user in a database named mysql (by default). The following query will return 1 if a user with the specified username exists, 0 otherwise.

SELECT EXISTS(SELECT 1 FROM mysql.user WHERE user = 'username')

If you're deleting the MySQL user anyways, then there's really no need to check if it exists first. MySQL won't throw any errors if there's nothing to delete:

DELETE FROM mysql.user WHERE User = 'username';