decode, base64 problem

Hi,

I don't know what this is about, so I could get from someone who knows
more PostgreSQL than I do,

some rational explanation of what the problem is.

I have a table that has a "lice" field that is of type byte and the
following 5 selects:

1. OK

2. error !

3. error ?

4. error ?
5. error !!!

1 -------------------------------------------------------

select

substring(encode(lice,'base64'), 110, 5) as Lokal0,
length(substring(encode(lice,'base64'), 110, 5)) as Len05

from grupa002.ispp_partner
where obrisan=0 and maticnibroj=30643;

 lokal0 | len05
--------+-------
 ICAgI  |     5
(1 row)

2 -------------------------------------------------------

select

substring(encode(lice,'base64'), 110, 5) as Lokal0,
length(substring(encode(lice,'base64'), 110, 5)) as Len05,

decode(substring(encode(lice,'base64'), 110, 5),'base64') as Lokal0decode

from grupa002.ispp_partner
where obrisan=0 and maticnibroj=30643;

ERROR:  22023: invalid end sequence
LOCATION:  b64_decode, encode.c:327

3. -------------------------------------------------------

select

substring(encode(lice,'base64'), 110, 5) as Lokal0,
length(substring(encode(lice,'base64'), 110, 5)) as Len05,

decode(substring(encode(lice,'base64'), 110, 5) || '=','base64') as
Lokal0decode

from grupa002.ispp_partner
where obrisan=0 and maticnibroj=30643;

ERROR:  22023: unexpected "="
LOCATION:  b64_decode, encode.c:295

4. -------------------------------------------------------

select

substring(encode(lice,'base64'), 110, 5) as Lokal0,
length(substring(encode(lice,'base64'), 110, 5)) as Len05,

decode(substring(encode(lice,'base64'), 110, 5) || '==','base64') as
Lokal0decode

from grupa002.ispp_partner
where obrisan=0 and maticnibroj=30643;

ERROR:  22023: unexpected "="
LOCATION:  b64_decode, encode.c:295

5. -------------------------------------------------------

select

substring(encode(lice,'base64'), 110, 5) as Lokal0,
length(substring(encode(lice,'base64'), 110, 5)) as Len05,

decode(/*substring(encode(lice,'base64'), 110, 5) ||
'=='*/'ICAgI','base64') as Lokal0decode

from grupa002.ispp_partner
where obrisan=0 and maticnibroj=30643;

ERROR:  22023: invalid end sequence
LOCATION:  b64_decode, encode.c:327
---------------------------------------------------------

My question is how to make a decode for a field for which encode text is
known and the length is 5?

Vladimir Kokovic, DP senior (69)
Serbia, Belgrade, May 22, 2020