https://www.postgresql.org/docs/9.6/static/functions-conditional.html

SELECT * FROM test;
 a
---
 1
 2
 3

SELECT a,
       CASE WHEN a=1 THEN 'one'
            WHEN a=2 THEN 'two'
            ELSE 'other'
       END
    FROM test;

 a | case
---+-------
 1 | one
 2 | two
 3 | other

SELECT a,
       CASE a WHEN 1 THEN 'one'
              WHEN 2 THEN 'two'
              ELSE 'other'
       END
    FROM test;

 a | case
---+-------
 1 | one
 2 | two
 3 | other



SELECT SUBSTR("Accounting"."ChartOfAccounts".Account, 7, 3) as "Act", 
       CASE SUBSTR("Accounting"."ChartOfAccounts".Account, 9, 1) 
   	       WHEN '0' THEN 'cero' 
   	       WHEN '1' THEN 'one' 
   	       WHEN '2' THEN 'two' 
   	       WHEN '3' THEN 'three' 
   	       WHEN '4' THEN 'four' 
              		ELSE 'other' 
       END AS "Ending" 
    FROM "ChartOfAccounts" LIMIT 20;