Arrays

Postgres allows columns to be defined as arrays of variable length. The type of the array can be an inbuilt type, a user-defined type or an enumerated type.

Declaring array columns in tables:

CREATE TABLE rock_band
(
 name text,
 members text[]
)

The above command will create a table rock_band with a text type column for the name of the band, and a column ‘members’ with a one-dimesional array to represent names of the members.

INSERT INTO rock_band
VALUES
('Led Zeppelin',
'{"Page", "Plant", "Jones", "Bonham"}'
)

Note that the array literals are double-quoted. Single quotes will give an error.

Querying the table will display:

postgres=# select * from rock_band;
 name | members 
--------------+---------------------------
 Led Zeppelin | {Page,Plant,Jones,Bonham}
(1 row)

An alternative syntax to insert is to use the array constructor:

INSERT INTO rock_band
VALUES
('Pink Floyd',
 ARRAY['Barrett', 'Gilmour']
)

When using the ARRAY constructor, the values are single-quoted.

postgres=# select * from rock_band;
 name | members 
--------------+---------------------------
 Led Zeppelin | {Page,Plant,Jones,Bonham}
 Pink Floyd | {Barrett,Gilmour}
(2 rows)

Array values can be accessed using subscripts or slices:

postgres=# select name from rock_band where members[2] = 'Plant';
 name 
--------------
 Led Zeppelin
(1 row)
postgres=# select members[1:2] from rock_band;
 members 
-------------------
 {Page,Plant}
 {Barrett,Gilmour}
(2 rows)

Arrays can be updated as a single element or as a whole:

Single-element update:

postgres=# UPDATE rock_band set members[2] = 'Waters' where name = 'Pink Floyd';
UPDATE 1
postgres=# select * from rock_band where name = 'Pink Floyd';
 name | members 
------------+------------------
 Pink Floyd | {Barrett,Waters}
(1 row)

Whole array update:

postgres=# UPDATE rock_band set members = '{"Mason", "Wright", "Gilmour"}' where name = 'Pink Floyd';
UPDATE 1 
postgres=# select * from rock_band where name = 'Pink Floyd'; 
name | members 
------------+------------------------
 Pink Floyd | {Mason,Wright,Gilmour}
(1 row)

To search for an array that has a particular value, the keyword ANY isused.

postgres=# select name from rock_band where 'Mason' = ANY(members);
 name 
------------
 Pink Floyd
(1 row)
postgres=# select name from rock_band where 'Barrett' = ANY(members);
 name
------
(0 rows)

To search if all values of the array match a value, ALL is used.

Article contributed by

Chandrakant Gopalan.