sql / expert
Snippet
User-Defined Type Constraints via CREATE DOMAIN
A DOMAIN is a global schema object that allows you to define a data type with localized constraints. Unlike simple column checks, domains promote reusability and centralize validation logic across multiple tables within the same database schema.
snippet.sql
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CREATE DOMAIN valid_email AS VARCHAR(255)CHECK (VALUE LIKE '%@%.%');CREATE TABLE subscribers (id INTEGER PRIMARY KEY,email valid_email);
Breakdown
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CREATE DOMAIN valid_email AS VARCHAR(255)
Initializes a custom domain based on the VARCHAR type.
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CHECK (VALUE LIKE '%@%.%')
Applies a constraint that every instance of this domain must contain an '@' and a dot.
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email valid_email
Uses the custom domain as the type for a table column, enforcing the pattern check automatically.