PostgreSQL 约束
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Postgresql constraint
提问by Ryan
I cannot seem to get this right, I am trying to modify a field to be a foreign key, with cascading delete... what am i doing wrong?
我似乎无法做到这一点，我正在尝试将字段修改为外键，并使用级联删除...我做错了什么？
ALTER TABLE my_table
ADD CONSTRAINT
FOREIGN KEY my_field
REFERENCES my_foreign_table
ON DELETE CASCADE;
回答by Magnus Hagander
It would help if you posted the error message. But I think you are just missing the parenthesis:
如果您发布错误消息会有所帮助。但我认为你只是缺少括号：
ALTER TABLE my_table
ADD CONSTRAINT my_fk
FOREIGN KEY (my_field)
REFERENCES my_foreign_table
ON DELETE CASCADE;
回答by Anonymous Coward
Just guessing: shouldn't you add a foreign key instead of a constraint?
只是猜测：您不应该添加外键而不是约束吗？
ALTER TABLE my_table ADD FOREIGN KEY (my_field) REFERENCES my_foreign_table;
回答by Tregoreg
I'm still somehow missing here an answer with foreign column (foreign_field) explicitly specified:
我仍然不知何故在这里缺少foreign_field明确指定的外列 ( )的答案：
ALTER TABLE my_table
ADD CONSTRAINT my_fk
FOREIGN KEY (my_field)
REFERENCES my_foreign_table (foreign_field)
ON DELETE CASCADE;
回答by Gerardo Cortés Mendoza
This works to me, I add the column to the table and then add the constraint with references to the other table:
这对我有用，我将列添加到表中，然后将约束添加到另一个表的引用：
-- add column to table
ALTER TABLE schema.table ADD COLUMN my_column type;
-- add constraint to column
ALTER TABLE schema.table ADD CONSTRAINT fk_name FOREIGN KEY (column)
REFERENCES schema.table (column) MATCH SIMPLE
ON UPDATE NO ACTION ON DELETE NO ACTION;
