Unique Indexes

Indexes can also be used to enforce uniqueness of a column's value, or the uniqueness of the combined values of more than one column.

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Indexes on Expressions

An index column need not be just a column of the underlying table, but can be a function or scalar expression computed from one or more columns of the table. This feature is

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Multicolumn Indexes

An index can be defined on more than one column of a table. For example, if you have a table of this form:

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Examining Index Usage

Although indexes in PostgreSQL do not need maintenance or tuning, it is still important to check which indexes are actually used by the real-life

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Index-Only Scans

All indexes in PostgreSQL are secondary indexes, meaning that each index is stored separately from the table's main

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Combining Multiple Indexes

A single index scan can only use query clauses that use the index's columns with operators of its operator class and are joined with AND. For example

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Operator Classes and Operator Families

An index definition can specify an operator class for each column of an index.

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Index Types

PostgreSQL provides several index types: B-tree, Hash, GiST, SP-GiST, GIN and BRIN. Each index type uses a different algorithm that is best

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Indexes and Collations

An index can support only one collation per index column. If multiple collations are of interest, multiple indexes may be needed. Consider these

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Partial Indexes

A partial index is an index built over a subset of a table; the subset is defined by a conditional expression (called the predicate

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