From https://graycarl.me/wiki/alembic

alembic_添加列自动产生Mysql的AFTER.py

# in env.py
from sqlalchemy.ext.compiler import compiles
from alembic.ddl.base import AddColumn, alter_table, add_column

@compiles(AddColumn)
def visit_add_column(element, compiler, **kw):
    sql = "%s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        add_column(compiler, element.column, **kw)
    )
    if 'after' in element.column.info:
        sql += ' AFTER `%s`' % element.column.info['after']
    return sql