15th April 2019: PostgreSQL Code of Conduct Committee 2018 Annual Report

Development Versions:
devel

PostgreSQL 8.4.22 Documentation | ||||
---|---|---|---|---|

Prev | Fast Backward | Appendix F. Additional Supplied Modules | Fast Forward | Next |

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

Table F-7. `intarray`
Functions

Function | Return Type | Description | Example | Result |
---|---|---|---|---|

`icount(int[])` |
int |
number of elements in array | icount('{1,2,3}'::int[]) |
3 |

```
sort(int[], text
dir)
``` |
int[] |
sort array — dir must be
asc or desc |
sort('{1,2,3}'::int[],
'desc') |
{3,2,1} |

`sort(int[])` |
int[] |
sort in ascending order | sort(array[11,77,44]) |
{11,44,77} |

`sort_asc(int[])` |
int[] |
sort in ascending order | ||

`sort_desc(int[])` |
int[] |
sort in descending order | ||

`uniq(int[])` |
int[] |
remove adjacent duplicates | uniq(sort('{1,2,3,2,1}'::int[])) |
{1,2,3} |

```
idx(int[], int
item)
``` |
int |
index of first element matching item (0 if none) |
idx(array[11,22,33,22,11],
22) |
2 |

```
subarray(int[], int start,
int len)
``` |
int[] |
portion of array starting at position start, len
elements |
subarray('{1,2,3,2,1}'::int[],
2, 3) |
{2,3,2} |

```
subarray(int[], int
start)
``` |
int[] |
portion of array starting at position start |
subarray('{1,2,3,2,1}'::int[],
2) |
{2,3,2,1} |

`intset(int)` |
int[] |
make single-element array | intset(42) |
{42} |

Table F-8. `intarray`
Operators

Operator | Returns | Description |
---|---|---|

int[] &&
int[] |
boolean |
overlap — true if arrays
have at least one common element |

int[] @> int[] |
boolean |
contains — true if left
array contains right array |

int[] <@ int[] |
boolean |
contained — true if left
array is contained in right array |

# int[] |
int |
number of elements in array |

int[] # int |
int |
index (same as `idx`
function) |

int[] + int |
int[] |
push element onto array (add it to end of array) |

int[] + int[] |
int[] |
array concatenation (right array added to the end of left one) |

int[] - int |
int[] |
remove entries matching right argument from array |

int[] - int[] |
int[] |
remove elements of right array from left |

int[] | int |
int[] |
union of arguments |

int[] | int[] |
int[] |
union of arrays |

int[] & int[] |
int[] |
intersection of arrays |

int[] @@ query_int |
boolean |
true if array satisfies
query (see below) |

query_int ~~ int[] |
boolean |
true if array satisfies
query (commutator of @@) |

(Before PostgreSQL 8.2, the containment operators `@>` and `<@` were
respectively called `@` and `~`. These names are still available, but are
deprecated and will eventually be retired. Notice that the old
names are reversed from the convention formerly followed by the
core geometric datatypes!)

The containment operators `@>` and
`<@` are approximately equivalent to
PostgreSQL's built-in
operators of the same names, except that they work only on
integer arrays while the built-in operators work for any array
type. An important difference is that `intarray`'s operators do not consider an empty
array to be contained in anything else. This is consistent with
the behavior of GIN-indexed queries, but not with the usual
mathematical definition of containment.

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.

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

Two 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.

There is also a non-default GIN operator class `gin__int_ops` supporting the same operators.

The choice between GiST and GIN indexing depends on the relative performance characteristics of GiST and GIN, which are discussed elsewhere. As a rule of thumb, a GIN index is faster to search than a GiST index, but slower to build or update; so GIN is better suited for static data and GiST for often-updated data.

```
-- a message can be in one or more "sections"
CREATE TABLE message (mid INT PRIMARY KEY, sections INT[], ...);
-- create specialized index
CREATE INDEX message_rdtree_idx ON message USING GIST (sections gist__int_ops);
-- 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;
```

The source directory `contrib/intarray/bench` contains a benchmark
test suite. To run:

cd .../bench createdb TEST psql TEST < ../_int.sql ./create_test.pl | psql TEST ./bench.pl

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

All work was done by Teodor Sigaev (`<teodor@sigaev.ru>`

) and
Oleg Bartunov (`<oleg@sai.msu.su>`

). See
http://www.sai.msu.su/~megera/postgres/gist for
additional information. Andrey Oktyabrski did a great work on
adding new functions and operations.