How to remove elements of array in PostgreSQL?

问题:

Is it possible to remove multiple elements from an array? Before removing elements Array1 is :

{1,2,3,4}

Array2 that contains some elements I wish to remove:

{1,4}

And I want to get:

 {2,3}

How to operate?

回答1:

Use unnest() with array_agg(), e.g.:

with cte(array1, array2) as (
    values (array[1,2,3,4], array[1,4])
    )
select array_agg(elem)
from cte, unnest(array1) elem
where elem <> all(array2);

 array_agg 
-----------
 {2,3}
(1 row)

If you often need this functionality, define the simple function:

create or replace function array_diff(array1 anyarray, array2 anyarray)
returns anyarray language sql immutable as $$
    select coalesce(array_agg(elem), '{}')
    from unnest(array1) elem
    where elem <> all(array2)
$$;

You can use the function for any array, not only int[]:

select array_diff(array['a','b','c','d'], array['a','d']);

 array_diff 
------------
 {b,c}
(1 row) 

回答2:

With the intarray extension, you can simply use -:

select '{1,2,3,4}'::int[] - '{1,4}'::int[]

Result:

{2,3}

Online demonstration

You'll need to install the intarray extension if you didn't already. It adds many convenient functions and operators if you're dealing with arrays of integers.

回答3:

With some help from this post:

select array_agg(elements) from 
   (select unnest('{1,2,3,4}'::int[]) 
except 
   select unnest('{1,4}'::int[])) t (elements)

Result:

{2,3}