PostgreSQL在逗号分隔的值列表中获取最后一个值

Question

In a PostgreSQL table I have a column which has values like

AX,B,C
A,BD
X,Y
J,K,L,M,N

In short , it will have a few comma separated strings in the column for each record. I wanted to get the last one in each record. I ended up with this.

select id, reverse(substr(reverse(mycolumn),1,position(',' in reverse(mycolumn)))) from mytable order by id ; 

Is there an easier way?

Answer 1

With regexp_replace :

select id, regexp_replace(mycolumn, '.*,', '')
from mytable
order by id;

Answer 2

我会这样：

select reverse(split_part(reverse(myColumn), ',', 1))

Answer 3

Is there an easier way?

With your current data, Gordon's answer works best imo. Other options would be a regex (messy), or converting the column to a text[] array eg ('{' || col || '}')::text[] or variations thereof.

If you were using a text[] array instead of plain text for your column, you'd want to use array functions directly:

select col[array_length(col, 1)]

http://www.postgresql.org/docs/current/static/functions-array.html

Example with dummy data:

 with bar as (
 select '{a,b,c}'::text[] as foo
 )
 select foo[array_length(foo, 1)] from bar;

You could, of course, also create a parse_csv() function or get_last_csv_value() function to avoid writing the above.