sql - 错误 : there is no unique constraint matching given keys for referenced table "bar"

Question

尝试在 Postgres 9.1 中创建此示例表结构:

CREATE TABLE foo (
    name        VARCHAR(256) PRIMARY KEY
);

CREATE TABLE bar (
    pkey        SERIAL PRIMARY KEY,
    foo_fk      VARCHAR(256) NOT NULL REFERENCES foo(name), 
    name        VARCHAR(256) NOT NULL, 
    UNIQUE (foo_fk,name)
);

CREATE TABLE baz(   
    pkey        SERIAL PRIMARY KEY,
    bar_fk      VARCHAR(256) NOT NULL REFERENCES bar(name),
    name        VARCHAR(256)
);

运行上面的代码会产生错误，这对我来说没有意义:

NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "foo_pkey" for table "foo"
NOTICE:  CREATE TABLE will create implicit sequence "bar_pkey_seq" for serial column "bar.pkey"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "bar_pkey" for table "bar"
NOTICE:  CREATE TABLE / UNIQUE will create implicit index "bar_foo_fk_name_key" for table "bar"
NOTICE:  CREATE TABLE will create implicit sequence "baz_pkey_seq" for serial column "baz.pkey"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "baz_pkey" for table "baz"
ERROR:  there is no unique constraint matching given keys for referenced table "bar"

********** Error **********

ERROR: there is no unique constraint matching given keys for referenced table "bar"
SQL state: 42830

谁能解释为什么会出现这个错误？

Answer 1

这是因为 name bar 上的专栏表没有UNIQUE 约束。

假设您在 bar 上有 2 行包含名称 'ams' 的表然后在 baz 上插入一行与 'ams'在 bar_fk , 哪一行在 bar 上是指因为有两行匹配吗？