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
