Thread: showing the DEFAULT of a field

Hi,
I'm new to psql and used mysql before. With mysql I could get with "show columns
from table 'table_name'" a table with the rows "Field", "Type", "NULL", "Key",
"Default" and "Extra".

But with "\d 'table_name'" in qsql I get only a table with the rows "Field",
"Type", and "Length". How can I get the other Information for example the
Default or if the field has the primary key? 

Klaus Woelfel

Hi.

Please look carefully at the sequence of commands:

shell#>createdb tmp
shell#>psql tmp
Welcome to the POSTGRESQL interactive sql monitor: Please read the file COPYRIGHT for copyright terms of POSTGRESQL
[PostgreSQL 6.5.2 on i386-pc-bsdi4.0.1, compiled by gcc 2.7.2.1]
  type \? for help on slash commands  type \q to quit  type \g or terminate with semicolon to execute queryYou are
currentlyconnected to the database: tmp
 

tmp=> \d
Couldn't find any tables, sequences or indices!
tmp=> create table test (i int4 primary key, j int4 default 1, t text not 
null);
NOTICE:  CREATE TABLE/PRIMARY KEY will create implicit index 'test_pkey' 
for table 'test'
CREATE
tmp=> \d
Database    = tmp+------------------+----------------------------------+----------+|  Owner           |
Relation            |   Type   |+------------------+----------------------------------+----------+| genov            |
test                            | table    || genov            | test_pkey                        | index
|+------------------+----------------------------------+----------+

tmp=> \d test
Table    = test
+----------------------------------+----------------------------------+-----
--+
|              Field               |              Type                | 
Length|
+----------------------------------+----------------------------------+-----
--+
| i                                | int4 not null                    |     
4 |
| j                                | int4 default 1                   |     
4 |
| t                                | text not null                    |   
var |
+----------------------------------+----------------------------------+-----
--+
Index:    test_pkey
tmp=> \q
shell#>pg_dump tmp
\connect - genov
CREATE TABLE "test" (       "i" int4 NOT NULL,       "j" int4 DEFAULT 1,       "t" text NOT NULL);
COPY "test" FROM stdin;
\.
CREATE UNIQUE INDEX "test_pkey" on "test" using btree ( "i" "int4_ops" );
shell#>

So, I hope you see how restrictions upon fields are expressed and created.
The probably confusing stuff is about the primary key. Primary keys are 
const-
ructed using unique indices upon the fields you say "primary key" about 
during
the creation of a table. These unique indices will not allow a duplicate 
value
in the field, which is, technically speaking, the primary goal of a primary 
key
field.

Watch this:
tmp=> insert into test (i) values (1);
ERROR:  ExecAppend: Fail to add null value in not null attribute t
tmp=> insert into test (i,t) values (1,'a line');
INSERT 31375 1
tmp=> insert into test (i,t) values (1,'another line');
ERROR:  Cannot insert a duplicate key into a unique index
tmp=> \q

This is it. If something is unclear, do write back.

Stoyan Genov