如何获取PostgreSQL文本中的最后一个元素？

Question

I have a text of elements seperated by , as follows:

'{4,56,7,3,2}'

the amount of elemets is unkonwn .

How do I get the last element? in the above example 2

Answer 1

Try this:

SELECT regexp_replace('4,56,7,3,2', '^.*,', '')

FIDDLE DEMO

EDIT:

Try

SELECT replace(replace(regexp_replace('4,56,7,3,2', '^.*,', ''),'{',''),'}','')

DEMO

Answer 2

You could use simple text manipulation functions LEFT , strpos and REVERSE :

SELECT val,
     CASE WHEN strpos(REVERSE(val),',') = 0 THEN val
          ELSE REVERSE(LEFT(REVERSE(val), strpos(REVERSE(val),',')-1))  
     END AS last_element
FROM tab;

SqlFiddleDemo

Output:

╔════════════════╦══════════════╗
║      val       ║ last_element ║
╠════════════════╬══════════════╣
║ 4,56,7,3,2     ║ 2            ║      
║ 1,11111,23121  ║ 23121        ║      
║ 123            ║ 123          ║
║ (null)         ║ (null)       ║
╚════════════════╩══════════════╝

EDIT:

WITH cte AS
(
    SELECT REPLACE(REPLACE(val, '{', ''), '}', '') AS val
    FROM tab
)
SELECT val,
     CASE WHEN strpos(REVERSE(val),',') = 0 THEN val
           ELSE REVERSE(LEFT(REVERSE(val), strpos(REVERSE(val),',')-1))  
     END AS last_element
FROM cte;

SqlFiddleDemo2

Answer 3

If the value is indeed stored with the curly braces you can simply cast it into an array and pick the last array element:

select (elements::text[])[array_length(elements::text[],1)]
from the_table;

As you didn't include the table definition, I assumed the column is named elements .

If the column does not contain the curly braces, but just a comma separated list of values, you can still use this approach:

select (string_to_array(elements,','))[array_length(string_to_array(elements,','), 1)]