ERROR: there is no unique constraint matching given keys for referenced table "bar"
Solution 1
It's because the name
column on the bar
table does not have the UNIQUE constraint.
So imagine you have 2 rows on the bar
table that contain the name 'ams'
and you insert a row on baz
with 'ams'
on bar_fk
, which row on bar
would it be referring since there are two rows matching?
Solution 2
In postgresql all foreign keys must reference a unique key in the parent table, so in your bar
table you must have a unique (name)
index.
See also http://www.postgresql.org/docs/9.1/static/ddl-constraints.html#DDL-CONSTRAINTS-FK and specifically:
Finally, we should mention that a foreign key must reference columns that either are a primary key or form a unique constraint.
Emphasis mine.
Solution 3
You should have name column as a unique constraint. here is a 3 lines of code to change your issues
-
First find out the primary key constraints by typing this code
\d table_name
you are shown like this at bottom
"some_constraint" PRIMARY KEY, btree (column)
-
Drop the constraint:
ALTER TABLE table_name DROP CONSTRAINT some_constraint
-
Add a new primary key column with existing one:
ALTER TABLE table_name ADD CONSTRAINT some_constraint PRIMARY KEY(COLUMN_NAME1,COLUMN_NAME2);
That's All.
Solution 4
when you do UNIQUE
as a table level constraint as you have done then what your defining is a bit like a composite primary key see ddl constraints, here is an extract
This specifies that the combination of values in the indicated columns is unique across the whole table, though any one of the columns need not be (and ordinarily isn't) unique.
this means that either field could possibly have a non unique value provided the combination is unique and this does not match your foreign key constraint.
most likely you want the constraint to be at column level. so rather then define them as table level constraints, 'append' UNIQUE
to the end of the column definition like name VARCHAR(60) NOT NULL UNIQUE
or specify indivdual table level constraints for each field.
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Comments
-
ams almost 2 years
Trying to create this example table structure in Postgres 9.1:
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) );
Running the above code produces an error, which does not make sense to me:
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
Can anyone explain why this error arises?
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ams almost 12 yearsColumn level constraint in my situation will not work I really should be defining a compound primary key, but I backed away from it because mapping it to JPA its a bit of a pain :)
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amphibient over 7 yearswhy isn't the declared PK considered as a unique constraint ? it's not like you can have a nonunique PK...
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Matteo Tassinari over 7 yearsIt must be unique on the table it "points to", because if it is not, the database engine will have no way to know which row you are actually referring to.
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Charming Robot over 5 yearsComposite keys? @amphibient
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Mufachir Hossain about 5 yearsI think having a unique key on the referenced column on parent table is not required in postgresql only but also it other RDBMSs too like oracle, sql server etc.
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Matteo Tassinari about 5 yearsMaybe, but certainly not all of them, for example MySQL requires just a simple index, which may be non unique
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Ninjakannon almost 5 yearsNote that the answer is true also for composite foreign keys, where a composite unique constraint or primary key is required on the parent table.
-
Marc Sloth Eastman over 4 years@CharmingRobot "it can be said that the PRIMARY KEY of a table is a combination of NOT NULL and UNIQUE constraint." w3resource.com/PostgreSQL/primary-key-constraint.php
-
Erwin Brandstetter almost 3 years@amphibient Because the
UNIQUE
constraint is required on the target column(s). The FK targetsbar.name
, but the PK is onbar.id
.