Getting list of values from column in QGIS

Question

I have one "column D" with a b c values for my entities (1-2-3-4). Something like that :

 1. b
 2. c
 3. c
 4. e
 5. j
 6. b

I would like to generate a list of each different value of "column D". so I would have b,c,e,j. How can I perform this?

Answer 1

Use the Field Calculator with this expression:

array_to_string(
    array_distinct(
        array_agg(expression:="column D")
        )
    )

This expression utilizes the following functions: array_to_string(), array_distinct(), and array_agg().

Answer 2

You can create a virtual layer to fetch the distinct values

Go to the menu Layer > Add Layer > Add/Edit Virtual Layer... and enter the query:

SELECT DISTINCT "column D"
FROM myLayer;

or to get it as a single list

SELECT group_concat(nme, ', ') 
FROM (
  SELECT DISTINCT "column D" as nme 
  FROM myLayer
)