como criar tabela no oracle

COMMENT ON TABLE <table_name> IS '<comment>';

Oracle cria tabela com valor padrão

CREATE TABLE EXP
(
NAME VARCHAR2(20),
SAL number(8,2) DEFAULT 800,
hire_date DATE DEFAULT SYSDATE ,
birthdate DATE DEFAULT SYSDATE -10
)

O Oracle cria alterações no valor padrão da tabela em 12c

Example:
create table test
(
id number generated as identity,
name varchar2(100),
email varchar2(100),
password varchar2(100),
firstname varchar2(100),
lastname varchar2(100)
);

Sequence as Default Value
With Oracle Database 12c, we can directly assign sequence nextval as a default value for a column, So you no longer need to create a trigger to populate the column with the next value of sequence, you just need to declare it with table definition.It is a sort of auto-increment feature for a column in oracle just like MySQL

Example:
create sequence tech_test_seq start with 1 increment by 1 nocycle;create table test
(
id number default tech_test_seq.nextval primary key
name varchar(30)
);

Tabelas e visualizações do dicionário de dados

Como listar todas as tabelas no Oracle

To list all tables owned by the current user, type:
select tablespace_name, table_name from user_tables;

To list all tables in a database:

select tablespace_name, table_name from dba_tables;

To list all tables accessible to the current user, type:

select tablespace_name, table_name from all_tables

To describe the table in SQLPLUS

desc <table_name>

Como determinar o tamanho da tabela

select
owner as "Schema"
, segment_name as "Object Name"
, segment_type as "Object Type"
, round(bytes/1024/1024,2) as "Object Size (Mb)"
, tablespace_name as "Tablespace"
from dba_segments
where segment_name=’<table_name>’;

Tabelas com número de linhas e comentários

select tab.owner as schema_name,
tab.table_name as table_name,
obj.created,
obj.last_ddl_time as last_modified,
tab.num_rows,
tab.last_analyzed,
comm.comments
from all_tables tab
inner join all_objects obj
on obj.owner = tab.owner
and obj.object_name = tab.table_name
left outer join all_tab_comments comm
on tab.table_name = comm.table_name
and tab.owner = comm.owner
where tab.owner = 'SCOTT'
order by tab.owner,
tab.table_name;

Perguntas frequentes sobre a tabela de criação do Oracle

SQL>CREATE TABLE "DEPT"
( "DEPTNO" NUMBER(2,0),
"DNAME" VARCHAR2(14),
"LOC" VARCHAR2(13),
CONSTRAINT "PK_DEPT" PRIMARY KEY ("DEPTNO")
)

SQL>CREATE TABLE "EMP"
( "EMPNO" NUMBER(4,0),
"ENAME" VARCHAR2(10),
"JOB" VARCHAR2(9),
"MGR" NUMBER(4,0),
"HIREDATE" DATE,
"SAL" NUMBER(7,2),
"COMM" NUMBER(7,2),
"DEPTNO" NUMBER(2,0),
CONSTRAINT "PK_EMP" PRIMARY KEY ("EMPNO"),
CONSTRAINT "FK_DEPTNO" FOREIGN KEY ("DEPTNO")
REFERENCES "DEPT" ("DEPTNO") ENABLE
);

SQL> desc emp
Name Null? Type
----------------------------------------- -------- -----------------------
EMPNO NOT NULL NUMBER(4)
ENAME VARCHAR2(10)
JOB VARCHAR2(9)
MGR NUMBER(4)
HIREDATE DATE
SAL NUMBER(7,2)
COMM NUMBER(7,2)
DEPTNO NUMBER(2)

SQL>

SQL> desc dept
Name Null? Type
----------------------------------------- -------- -----------------------

DEPTNO NOT NULL NUMBER(2)
DNAME VARCHAR2(14)
LOC VARCHAR2(13)

SQL>

insert into DEPT values(10, 'ACCOUNTING', 'NEW YORK');
insert into dept values(20, 'RESEARCH', 'DALLAS');
insert into dept values(30, 'RESEARCH', 'DELHI');
insert into dept values(40, 'RESEARCH', 'MUMBAI');

insert into emp values( 7698, 'Blake', 'MANAGER', 7839, to_date('1-5-2007','dd-mm-yyyy'), 2850, null, 10 );
insert into emp values( 7782, 'Clark', 'MANAGER', 7839, to_date('9-6-2008','dd-mm-yyyy'), 2450, null, 10 );
insert into emp values( 7788, 'Scott', 'ANALYST', 7566, to_date('9-6-2012','dd-mm-yyyy'), 3000, null, 20 );

insert into emp values( 7789, 'TPM', 'ANALYST', 7566, to_date('9-6-2017','dd-mm-yyyy'), 3000, null, null );
insert into emp values( 7560, 'T1OM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, 20 );
insert into emp values( 7790, 'TOM', 'ANALYST', 7567, to_date('9-7-2017','dd-mm-yyyy'), 4000, null, null );

SQL> select * from emp;
EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO
---------- ---------- --------- ---------- --------- ---------- ---------- ----------
7698 BLAKE MANAGER 7839 01-MAY-07 2850 10
7782 CLARK MANAGER 7839 09-JUN-08 2450 10
7788 SCOTT ANALYST 7566 09-JUN-12 3000 20
7789 TPM ANALYST 7566 09-JUN-17 3000
7790 TOM ANALYST 7567 09-JUL-17 4000
7560 T1OM ANALYST 7567 09-JUL-17 4000 20

After the practice is over, you can drop the tables
SQL>drop table emp;

SQL>drop table dept;