Domain types for validation in PostgreSQL - Step-by-Step Execution

Concept Flow - Domain types for validation

Define Domain with Base Type

↓

Add Validation Constraints

↓

Use Domain in Table Columns

↓

Insert Data

↓

Validation Checks Applied

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Data Stored

You define a domain with a base type and constraints, then use it in tables. When inserting data, PostgreSQL checks constraints and accepts or rejects the data.

Execution Sample

PostgreSQL

CREATE DOMAIN us_postal_code AS TEXT
  CHECK (VALUE ~ '^\d{5}(-\d{4})?$');

CREATE TABLE addresses (
  id SERIAL PRIMARY KEY,
  postal_code us_postal_code
);

INSERT INTO addresses (postal_code) VALUES ('12345');
INSERT INTO addresses (postal_code) VALUES ('ABCDE');

Defines a domain for US postal codes with a regex check, creates a table using it, then inserts one valid and one invalid postal code.

Execution Table

Step	Action	Input/Value	Validation Result	Outcome
1	Create domain us_postal_code	TEXT with regex check	Domain created	Domain ready for use
2	Create table addresses	id SERIAL, postal_code us_postal_code	Table created	Table ready for data
3	Insert postal_code '12345'	'12345'	Matches regex	Row inserted successfully
4	Insert postal_code 'ABCDE'	'ABCDE'	Does not match regex	Error: check constraint violation

💡 Execution stops on error at step 4 due to invalid postal code format

Variable Tracker

Variable	Start	After Step 3	After Step 4
postal_code	undefined	'12345' accepted	'ABCDE' rejected

Key Moments - 2 Insights

Why does the second insert fail even though the column type is TEXT?

Because the domain us_postal_code has a check constraint that requires the value to match a specific regex pattern. The value 'ABCDE' does not match, so PostgreSQL rejects it (see execution_table step 4).

Can I use the domain type in multiple tables?

Yes, once defined, the domain type can be used in any table column just like a regular data type, enforcing the same validation everywhere.

Visual Quiz - 3 Questions

Look at the execution_table, what happens at step 3 when inserting '12345'?

A The value fails validation and raises an error

B The value matches the regex and is inserted successfully

C The value is converted to a number before insertion

D The domain is redefined at this step

💡 Hint

Check the Validation Result and Outcome columns at step 3 in the execution_table

At which step does the check constraint cause an error?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look at the Validation Result and Outcome columns for each step in the execution_table

If the regex in the domain was changed to allow letters, how would the execution_table change?

A Step 3 would fail instead

B The domain creation would fail at step 1

C Step 4 would succeed and insert the value

D No change would happen

💡 Hint

Think about how the Validation Result and Outcome depend on the regex check in the domain

Concept Snapshot

CREATE DOMAIN name AS base_type
  CHECK (condition);
Use domain as column type.
PostgreSQL enforces constraints on insert/update.
Invalid data causes errors, valid data stores normally.

Full Transcript

This visual execution shows how PostgreSQL domain types work for validation. First, a domain is created with a base type and a check constraint using a regex pattern. Then a table is created using this domain as a column type. When inserting data, PostgreSQL checks if the value matches the domain's constraint. If it matches, the row is inserted successfully. If not, an error is raised and insertion fails. This ensures data validity at the database level. Domains can be reused in multiple tables for consistent validation.