Concatenate three columns data into one column in Postgres

Question

Can anyone tell me which command is used for concatenate three columns data into one column in PostgreSQL database?

e.g.

If the columns are

begin | Month | Year
   12 |     1 | 1988
   13 |     3 | 1900
   14 |     4 | 2000
   15 |     5 | 2012

result like

Begin
12-1-1988 
13-3-1900
14-4-2000
15-5-2012

Answer 1

Just use concatenation operator || : http://www.sqlfiddle.com/#!1/d66bb/2

select begin || '-' || month || '-' || year as begin 
from t;

Output:

|     BEGIN |
-------------
| 12-1-1988 |
| 13-3-1900 |
| 14-4-2000 |
| 15-5-2012 |

---

If you want to change the begin column itself, begin column must be of string type first, then do this: http://www.sqlfiddle.com/#!1/13210/2

update t set begin = begin || '-' || month || '-' || year ;

Output:

|     BEGIN |
-------------
| 12-1-1988 |
| 13-3-1900 |
| 14-4-2000 |
| 15-5-2012 |

---

UPDATE

About this:

but m not getting null value column date

Use this:

select (begin || '-' || month || '-' || year)::date as begin 
from t