在flask项目中，我已经迁移了db，并在运行升级脚本以更新表之后。 升级后的结果给了我重复的外键：

    projectsreal | CREATE TABLE `projectsreal` (
  `id` int(11) NOT NULL AUTO_INCREMENT,`projid` int(11) NOT NULL,`memberprj` int(11) DEFAULT NULL,`contrib` int(11) NOT NULL,PRIMARY KEY (`id`),UNIQUE KEY `IS_Projectsreal` (`projid`,`memberprj`),**KEY `memberprj` (`memberprj`),CONSTRAINT `projectsreal_ibfk_1` FOREIGN KEY (`projid`) REFERENCES `projects` (`projid`) ON DELETE CASCADE,CONSTRAINT `projectsreal_ibfk_10` FOREIGN KEY (`memberprj`) REFERENCES `users` (`id`),CONSTRAINT `projectsreal_ibfk_11` FOREIGN KEY (`projid`) REFERENCES `projects` (`projid`) ON DELETE CASCADE,CONSTRAINT `projectsreal_ibfk_12` FOREIGN KEY (`memberprj`) REFERENCES `users` (`id`)**,...

Alembic给出的脚本修订如下：

    # revision identifiers,used by Alembic.
revision = '5117277c7aa5'
down_revision = '9a67f348194a'

from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import mysql

def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    #op.add_column('projectsreal',sa.Column('memberprj',sa.INTEGER(),nullable=True))
    op.create_foreign_key(None,'projectsreal','projects',['projid'],ondelete='CASCADE')
    op.create_foreign_key(None,'users',['memberprj'],['id'])
    op.execute("""CREATE UNIQUE INDEX IS_TaxonomyNameLow ON taxonomy (lower(display_name))""")

是由于op.create_foreign_key(None,'projectspriv',ondelete='CASCADE') 中未命名的ForeignKey吗？