Supported Versions: Current (14) / 13 / 12 / 11 / 10
Development Versions: 15 / devel
Unsupported versions: 9.6 / 9.5 / 9.4 / 9.3 / 9.2 / 9.1 / 9.0 / 8.4 / 8.3

## F.18. intarray

The `intarray` module provides a number of useful functions and operators for manipulating null-free arrays of integers. There is also support for indexed searches using some of the operators.

All of these operations will throw an error if a supplied array contains any NULL elements.

Many of these operations are only sensible for one-dimensional arrays. Although they will accept input arrays of more dimensions, the data is treated as though it were a linear array in storage order.

This module is considered trusted, that is, it can be installed by non-superusers who have `CREATE` privilege on the current database.

### F.18.1. `intarray` Functions and Operators

The functions provided by the `intarray` module are shown in Table F.9, the operators in Table F.10.

Table F.9. `intarray` Functions

Function

Description

Example(s)

`icount` ( `integer[]` ) → `integer`

Returns the number of elements in the array.

`icount('{1,2,3}'::integer[])``3`

`sort` ( `integer[]`, `dir` `text` ) → `integer[]`

Sorts the array in either ascending or descending order. `dir` must be `asc` or `desc`.

`sort('{1,3,2}'::integer[], 'desc')``{3,2,1}`

`sort` ( `integer[]` ) → `integer[]`

`sort_asc` ( `integer[]` ) → `integer[]`

Sorts in ascending order.

`sort(array[11,77,44])``{11,44,77}`

`sort_desc` ( `integer[]` ) → `integer[]`

Sorts in descending order.

`sort_desc(array[11,77,44])``{77,44,11}`

`uniq` ( `integer[]` ) → `integer[]`

`uniq(sort('{1,2,3,2,1}'::integer[]))``{1,2,3}`

`idx` ( `integer[]`, `item` `integer` ) → `integer`

Returns index of the first array element matching `item`, or 0 if no match.

`idx(array[11,22,33,22,11], 22)``2`

`subarray` ( `integer[]`, `start` `integer`, `len` `integer` ) → `integer[]`

Extracts the portion of the array starting at position `start`, with `len` elements.

`subarray('{1,2,3,2,1}'::integer[], 2, 3)``{2,3,2}`

`subarray` ( `integer[]`, `start` `integer` ) → `integer[]`

Extracts the portion of the array starting at position `start`.

`subarray('{1,2,3,2,1}'::integer[], 2)``{2,3,2,1}`

`intset` ( `integer` ) → `integer[]`

Makes a single-element array.

`intset(42)``{42}`

Table F.10. `intarray` Operators

Operator

Description

`integer[]` `&&` `integer[]``boolean`

Do arrays overlap (have at least one element in common)?

`integer[]` `@>` `integer[]``boolean`

Does left array contain right array?

`integer[]` `<@` `integer[]``boolean`

Is left array contained in right array?

`#` `integer[]``integer`

Returns the number of elements in the array.

`integer[]` `#` `integer``integer`

Returns index of the first array element matching the right argument, or 0 if no match. (Same as `idx` function.)

`integer[]` `+` `integer``integer[]`

Adds element to end of array.

`integer[]` `+` `integer[]``integer[]`

Concatenates the arrays.

`integer[]` `-` `integer``integer[]`

Removes entries matching the right argument from the array.

`integer[]` `-` `integer[]``integer[]`

Removes elements of the right array from the left array.

`integer[]` `|` `integer``integer[]`

Computes the union of the arguments.

`integer[]` `|` `integer[]``integer[]`

Computes the union of the arguments.

`integer[]` `&` `integer[]``integer[]`

Computes the intersection of the arguments.

`integer[]` `@@` `query_int``boolean`

Does array satisfy query? (see below)

`query_int` `~~` `integer[]``boolean`

Does array satisfy query? (commutator of `@@`)

The operators `&&`, `@>` and `<@` are equivalent to PostgreSQL's built-in operators of the same names, except that they work only on integer arrays that do not contain nulls, while the built-in operators work for any array type. This restriction makes them faster than the built-in operators in many cases.

The `@@` and `~~` operators test whether an array satisfies a query, which is expressed as a value of a specialized data type `query_int`. A query consists of integer values that are checked against the elements of the array, possibly combined using the operators `&` (AND), `|` (OR), and `!` (NOT). Parentheses can be used as needed. For example, the query `1&(2|3)` matches arrays that contain 1 and also contain either 2 or 3.

### F.18.2. Index Support

`intarray` provides index support for the `&&`, `@>`, and `@@` operators, as well as regular array equality.

Two parameterized GiST index operator classes are provided: `gist__int_ops` (used by default) is suitable for small- to medium-size data sets, while `gist__intbig_ops` uses a larger signature and is more suitable for indexing large data sets (i.e., columns containing a large number of distinct array values). The implementation uses an RD-tree data structure with built-in lossy compression.

`gist__int_ops` approximates an integer set as an array of integer ranges. Its optional integer parameter `numranges` determines the maximum number of ranges in one index key. The default value of `numranges` is 100. Valid values are between 1 and 253. Using larger arrays as GiST index keys leads to a more precise search (scanning a smaller fraction of the index and fewer heap pages), at the cost of a larger index.

`gist__intbig_ops` approximates an integer set as a bitmap signature. Its optional integer parameter `siglen` determines the signature length in bytes. The default signature length is 16 bytes. Valid values of signature length are between 1 and 2024 bytes. Longer signatures lead to a more precise search (scanning a smaller fraction of the index and fewer heap pages), at the cost of a larger index.

There is also a non-default GIN operator class `gin__int_ops`, which supports these operators as well as `<@`.

The choice between GiST and GIN indexing depends on the relative performance characteristics of GiST and GIN, which are discussed elsewhere.

### F.18.3. Example

```-- a message can be in one or more “sections”
CREATE TABLE message (mid INT PRIMARY KEY, sections INT[], ...);

-- create specialized index with signature length of 32 bytes
CREATE INDEX message_rdtree_idx ON message USING GIST (sections gist__intbig_ops (siglen = 32));

-- select messages in section 1 OR 2 - OVERLAP operator
SELECT message.mid FROM message WHERE message.sections && '{1,2}';

-- select messages in sections 1 AND 2 - CONTAINS operator
SELECT message.mid FROM message WHERE message.sections @> '{1,2}';

-- the same, using QUERY operator
SELECT message.mid FROM message WHERE message.sections @@ '1&2'::query_int;
```

### F.18.4. Benchmark

The source directory `contrib/intarray/bench` contains a benchmark test suite, which can be run against an installed PostgreSQL server. (It also requires `DBD::Pg` to be installed.) To run:

```cd .../contrib/intarray/bench
createdb TEST
psql -c "CREATE EXTENSION intarray" TEST
./create_test.pl | psql TEST
./bench.pl
```

The `bench.pl` script has numerous options, which are displayed when it is run without any arguments.

### F.18.5. Authors

All work was done by Teodor Sigaev () and Oleg Bartunov (). See http://www.sai.msu.su/~megera/postgres/gist/ for additional information. Andrey Oktyabrski did a great work on adding new functions and operations.

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