// Docker is unable to map the mysql folder containing the socket file.

// Change the following line in the volumes property of your db container in the docker-compose.yml from
- 'sail-mysql:/var/lib/mysql' 

// to 
'- '${MYSQL_DOCKER_FOLDER}:/var/lib/mysql'

// The corresponding env variable might hold something like MYSQL_DOCKER_FOLDER=./mysql

// Create the "mysql" folder at the root of the file