Use Replace Function in Case When Condition

Question

Table Name is tabelea columns are name,expdate . Both Column have not null contraints. Both column had character varying data type.

Values

name expdate

A     '10-05-2015'
B     '    '

Now i want to fetch the value which expdate is not empty then convert to date format otherwise so empty. So i tried like this

select name,case when replace(expdate,' ','') <> '' then
to_char(cast(expdate as date),'dd-MM-yyyy') else null end from tablea

But is not work its show error invalid input syntax for type date: "' '" .

How to solve this?

i tried trim also.

Postgresql 9.3

Answer 1

You can combine that in a single call if you convert empty strings to a null value:

select name,
       to_char(cast(nullif(trim(expdate), '') as date),'dd-MM-yyyy') 
from tablea;

The cast relies on some implicit data type conversion. It would be better to use to_date() with an explicit format instead:

to_char(to_date(nullif(trim(expdate), ''), 'dd-mm-yyyy'),'dd-MM-yyyy') 

SQLFiddle example: http://sqlfiddle.com/#!15/a9831/1

Answer 2

You can use the tilde to compare your string with the desired date pattern, before making it a date:

select
  name,
  case when expdate ~ '^[[:digit:]]{2}-[[:digit:]]{2}-[[:digit:]]{4}$' then
    to_date(expdate, 'dd-MM-yyyy')
  else
    null
  end as the_date
from tablea;

(Of course it is a bad idea to use a string data type to store dates in the first place.)

SQL fiddle: http://sqlfiddle.com/#!15/a66cf/2 .