PostgreSQL array_cat() Function

The PostgreSQL array_cat() function concatenates two specified arrays into one array and returns the result array.

`array_cat()` Syntax

Here is the syntax of the PostgreSQL array_cat() function:

array_cat(array1, array2) -> array

The PostgreSQL array_cat() function returns an array, which is the concatenation of two arrays.

The two arrays to be concatenated should have the same data type, otherwise the array_cat() function will give an error message.

If one of the arguments is NULL, the function array_cat() returns another array that is not NULL.

If both arguments are NULL, the array_cat() function will return NULL.

This example shows how to use the PostgreSQL array_cat() function to concatenate two integer arrays: {0,1,2} and {3,4,5}.

SELECT array_cat(ARRAY[0, 1, 2], ARRAY[3, 4, 5]);

   array_cat
---------------
 {0,1,2,3,4,5}

You can also use the array_cat() function to concatenate two string arrays:

SELECT
    array_cat(
        ARRAY['zero', 'one', 'two'],
        ARRAY['three', 'four', 'five']
    );

           array_cat
--------------------------------
 {zero,one,two,three,four,five}

If one of the arguments is NULL, the array_cat() function returns another array that is not NULL. E.g:

SELECT
    array_cat(ARRAY[0, 1, 2], NULL),
    array_cat(NULL, ARRAY[3, 4, 5]);

 array_cat | array_cat
-----------+-----------
 {0,1,2}   | {3,4,5}

You cannot concatenate two arrays of different data types. For example, you cannot concatenate an integer array with an string array like this:

SELECT
    array_cat(
        ARRAY[0, 1, 2],
        ARRAY['three', 'four', 'five']
    );

The array_cat() function will give an error.