Generated column and inheritance: strange default error
| От | Rémi Cura |
|---|---|
| Тема | Generated column and inheritance: strange default error |
| Дата | |
| Msg-id | CAJvUf_u4h0DxkCMCeEKAWCuzGUTnDP-G5iVmSwxLQSXn0_FWNQ@mail.gmail.com обсуждение исходный текст |
| Список | pgsql-hackers |
Hello dear Hackers,
I encountered a strange issue with generated column and inheritance.
The core of the problem is that when inheriting from a table, you can re-declare the same column (provided it has the same type).
But when doing this and introducing a generated column, an error is raised
`[0A000] ERROR: cannot use column reference in DEFAULT expression`
This is too bad, as generated columns are an awesome new feature.
I don't think that is an expected behavior, and at the very least the error is misleading.
Here is a super short synthetic demo, along with 2 workarounds
```SQL
---- testing an issue with inheritance and generated columnDROP SCHEMA IF EXISTS test_inheritance_and_generated_column CASCADE ;
CREATE SCHEMA IF NOT EXISTS test_inheritance_and_generated_column ;
----------------------------------------------------------------------------------------------------
--- ERROR (set a generated column in an inherited table)
DROP TABLE IF EXISTS test_inheritance_and_generated_column.parent_table CASCADE;
CREATE TABLE test_inheritance_and_generated_column.parent_table(
science_grade float DEFAULT 0.7
, avg_grade float
);
-- THIS RAISE THE ERROR : [0A000] ERROR: cannot use column reference in DEFAULT expression
DROP TABLE IF EXISTS test_inheritance_and_generated_column.child_basic;
CREATE TABLE test_inheritance_and_generated_column.child_basic(
literature_grade float DEFAULT 0.3,
-- avg_grade float is inherited
avg_grade float GENERATED ALWAYS AS ( (science_grade+literature_grade)/2.0 ) STORED
)INHERITS (test_inheritance_and_generated_column.parent_table);
------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------
--- WORKS (removing the column from parent)
DROP TABLE IF EXISTS test_inheritance_and_generated_column.parent_table CASCADE;
CREATE TABLE test_inheritance_and_generated_column.parent_table(
science_grade float DEFAULT 0.7
-- , avg_grade float
);
--
DROP TABLE IF EXISTS test_inheritance_and_generated_column.child_basic;
CREATE TABLE test_inheritance_and_generated_column.child_basic(
literature_grade float DEFAULT 0.3,
avg_grade float GENERATED ALWAYS AS ( (science_grade+literature_grade)/2.0 ) STORED
)INHERITS (test_inheritance_and_generated_column.parent_table);
------------------------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------
-- THIS WORKS (droping inheritance, dropping column, creating column with generating, adding inheritance )
DROP TABLE IF EXISTS test_inheritance_and_generated_column.parent_table CASCADE;
CREATE TABLE test_inheritance_and_generated_column.parent_table(
science_grade float DEFAULT 0.7
, avg_grade float
);
--
DROP TABLE IF EXISTS test_inheritance_and_generated_column.child_basic;
CREATE TABLE test_inheritance_and_generated_column.child_basic(
literature_grade float DEFAULT 0.3,
avg_grade float
)INHERITS (test_inheritance_and_generated_column.parent_table);
ALTER TABLE test_inheritance_and_generated_column.child_basic NO INHERIT test_inheritance_and_generated_column.parent_table;
ALTER TABLE test_inheritance_and_generated_column.child_basic DROP COLUMN avg_grade;
ALTER TABLE test_inheritance_and_generated_column.child_basic
ADD COLUMN avg_grade float GENERATED ALWAYS AS ( (science_grade+literature_grade)/2.0 ) STORED;
ALTER TABLE test_inheritance_and_generated_column.child_basic INHERIT test_inheritance_and_generated_column.parent_table;
----------------------------------------------------------------------------------------------------
```
PostgreSQL 12.2 (Ubuntu 12.2-2.pgdg18.04+1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0, 64-bit
Cheers,
Remi-C
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