How deeply does Just Use Postgres! cover unique constraint?

Defines uniqueness and explains its foreign-key and index implications, but does not demonstrate creating a standalone unique constraint.

Unique constraint

As explained in Just Use Postgres!

A unique constraint requires that values in a specified column or set of columns be distinct within a table.

A unique constraint protects data integrity by requiring values in a specified column or group of columns to remain distinct within a table. section 2.3.1

A unique constraint supports relational integrity by:

Preventing duplicate values in the constrained column or column group. section 2.3.1
Allowing a foreign key to reference a column that is not a primary key, provided that column has an associated unique constraint. section 2.3.2
Supporting fast foreign-key verification through the index created for unique columns. section 2.3.2

Using a primary key as the unique reference

The products.catalog table uses id as its primary key, so id is unique by definition and can be referenced by products.reviews.product_id. A foreign-key definition would fail if the referenced catalog column had no matching unique constraint. section 2.3.2

How Just Use Postgres! covers it

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Also explained in

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Grokking Relational Database DesignA unique constraint is a database rule requiring every value, or every combined value across specified columns, to be distinct.
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Coding with AIA unique constraint is a database rule requiring values in a column or column group to be distinct across records.
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Graph Algorithms for Data ScienceA unique constraint is a database rule requiring specified property values to be unique among the records or graph elements to which it applies.
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Building User-Friendly DSLsA constraint that detects sufficiently similar neighboring or related things whose names are too similar or equal.
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Java Persistence with Spring Data and Hibernate epubA database constraint that requires each non-null value or combination of values in specified columns to be unique.
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Learn SQL in a Month of LunchesA unique constraint is a database rule requiring non-null values in a column or column set to be distinct.

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Related concepts

constraintkind of · A constraint is a condition or rule that restricts the permissible states, values, actions, or solutions in a system or problem.
attributeconfigures · An attribute is a named property, value, or piece of information associated with an entity, object, or program element.
nonclustered indexproduces · A nonclustered index is a separate database structure that stores keys and row locators without determining a table’s physical row order.
indexingproduces · Indexing is the organization or use of positions, keys, or lookup structures to identify and retrieve selected data or elements.
association resourceused by · An association resource is an API resource that represents a relationship between specific resources and whose associated endpoints are fixed for the resource's lifetime.
B-treeproduces · A B-tree is a balanced multiway search tree that maintains ordered keys and supports efficient searching, insertion, deletion, and sequential access.

This explainer was generated by Manning's knowledge graph from the text of Just Use Postgres!. The section links point to the parts of the book it draws on.