Questions about "varchar" NOT NULL default = char(1) ?

Emi Lu wrote:

Greetings,

If one column "col1" is defined as :

col1 varchar(1) not null default ''

Does it means that col1's definition is equal to

col1 char(1) not null default ''

Not quite; for example,

neilc=# create table t1 (x char(1) not null);
CREATE TABLE
neilc=# create table t2 (x varchar(1) not null);
CREATE TABLE
neilc=# insert into t1 values ('');
INSERT 0 1
neilc=# insert into t2 values ('');
INSERT 0 1
neilc=# select octet_length(x) from t1;
octet_length
--------------
1
(1 row)

neilc=# select octet_length(x) from t2;
octet_length
--------------
0
(1 row)

Put it another way, will char '' be saved as char(1) or char '' does not
use space at all?

I'm not sure what you mean.

-Neil