How-to : https://blog.thrsh.net/339-mac-win-1-docs-root-mysql-data.html

unisql.sh

#!/bin/bash

# Simple workaround change MAMP PRO default MySQL data path
# http://stackoverflow.com/questions/4745822/mac-os-x-mysql-custom-database-path-mamp-pro
# @cecekpawon - https://blog.thrsh.net

# Start: EDIT
# Default MAMP PRO MySQL data path
mamppath="/Library/Application Support/appsolute/MAMP PRO/db"
mampsql="${mamppath}/mysql"
# Our MySQL data BACKUP path
mysqlbkp="${mamppath}/mysqlbkp"
# Our NEW MySQL data path
unipath="/Volumes/XDATA/localhost"
unisql="${unipath}/mysql"
# End: EDIT

# Check symlink
echo "Checking existing symlink.."
if [[ -L "${mampsql}" ]]; then
  echo "Symlink exist.. Removing"
  rm "${mampsql}"
fi

# Check backup
echo "Checking existing backup.."
if [[ -d "${mysqlbkp}" ]]; then
  echo "Backup exist.. Restoring"
  cp -R  "${mysqlbkp}" "${mampsql}"
fi

# Rename / backup MAMP PRO MySQL data
if [[ -d "${mampsql}" ]]; then
  # Copy existing MAMP PRO MySQL data
  echo "Copying MySQL data to new path.."
  cp -R "${mampsql}" "${unipath}"

  # Rename / backup MAMP PRO MySQL data
  echo "Create backup.."
  if [[ ! -d "${mysqlbkp}" ]]; then
    mv "${mampsql}" "${mysqlbkp}"
  else
    rm -rf "${mampsql}"
  fi

  # Create symlink to our NEW MySQL data path
  ln -s "${unisql}" "${mampsql}"

  # Check symlink
  if [[ -L "${mampsql}" ]]; then
    echo "Done: Symlink created (to: ${unisql})"
  else
    echo "Done: Fail to create Symlink.."
  fi
else
  echo "Done: Fail to locate source: (from: ${mampsql}).."
fi