How do I select a subset of an array in Postgres?

Question

Assuming I have an array in one of my postgres columns:

> select array[1,2,3,4];
   array   
-----------
 {1,2,3,4} 

How do I select a subset of the items from that array, in general? For instance, if I want to select items from the x index to the y index, how would I grab the items in that range (x to y)?

I'm using PostgreSQL 9.4.

Answer 1

From the fine manual:

8.15.3. Accessing Arrays
[...]
We can also access arbitrary rectangular slices of an array, or subarrays. An array slice is denoted by writing lower-bound:upper-bound for one or more array dimensions.
[...]
It is possible to omit the lower-bound and/or upper-bound of a slice specifier; the missing bound is replaced by the lower or upper limit of the array's subscripts.

For example:

=> select (array[1,2,3,4,5,6])[2:5];
   array   
-----------
 {2,3,4,5}
(1 row)

=> select (array[1,2,3,4,5,6])[:5];
    array    
-------------
 {1,2,3,4,5}
(1 row)

=> select (array[1,2,3,4,5,6])[2:];
    array    
-------------
 {2,3,4,5,6}
(1 row)

=> select (array[1,2,3,4,5,6])[:];
     array     
---------------
 {1,2,3,4,5,6}
(1 row)

So to get a slice from index x to y (inclusive), you'd say:

array_column[x:y]