Oracle：
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) DNAME VARCHAR2(100) SQL> SQL> alter table emp modify ename varchar2(20) default ' '; Table altered.
LightDB：
lightdb@postgres=# alter table emp alter column ename type varchar2(20);
ALTER TABLE
lightdb@postgres=# alter table emp alter column ename set default ' ';
ALTER TABLE
lightdb@postgres=# \d emp
Table "public.emp"
Column | Type | Collation | Nullable | Default
----------+---------------+-----------+----------+---------------
empno | numeric(4,0) | | not null |
ename | varchar2(20) | | | ' '::varchar2
job | varchar2(9) | | |
mgr | numeric(4,0) | | |
hiredate | date | | |
sal | numeric(7,2) | | |
comm | numeric(7,2) | | |
deptno | numeric(2,0) | | |
dname | varchar2(100) | | |
Indexes:
"pk_emp" PRIMARY KEY, btree (empno)
lightdb@postgres=# \h alter table
Command: ALTER TABLE
Description: change the definition of a table
Syntax:
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
action [, ... ]
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
RENAME [ COLUMN ] column_name TO new_column_name
ALTER TABLE [ IF EXISTS ] [ ONLY ] name [ * ]
RENAME CONSTRAINT constraint_name TO new_constraint_name
ALTER TABLE [ IF EXISTS ] name
RENAME TO new_name
ALTER TABLE name WITH UPDATE CURRENT_TIMESTAMP
ALTER TABLE name WITH PRIMARY KEY [ smallserial | serial | bigserial ]
ALTER TABLE [ IF EXISTS ] name
SET SCHEMA new_schema
ALTER TABLE ALL IN TABLESPACE name [ OWNED BY role_name [, ... ] ]
SET TABLESPACE new_tablespace [ NOWAIT ]
ALTER TABLE [ IF EXISTS ] name
ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }
ALTER TABLE [ IF EXISTS ] name
DETACH PARTITION partition_name
where action is one of:
ADD [ COLUMN ] [ IF NOT EXISTS ] column_name data_type [ COLLATE collation ] [ column_constraint [ ... ] ]
DROP [ COLUMN ] [ IF EXISTS ] column_name [ RESTRICT | CASCADE ]
ALTER [ COLUMN ] column_name [ SET DATA ] TYPE data_type [ COLLATE collation ] [ USING expression ]
ALTER [ COLUMN ] column_name SET DEFAULT expression
ALTER [ COLUMN ] column_name DROP DEFAULT
ALTER [ COLUMN ] column_name { SET | DROP } NOT NULL
ALTER [ COLUMN ] column_name DROP EXPRESSION [ IF EXISTS ]
ALTER [ COLUMN ] column_name ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ]
ALTER [ COLUMN ] column_name { SET GENERATED { ALWAYS | BY DEFAULT } | SET sequence_option | RESTART [ [ WITH ] restart ] } [...]
ALTER [ COLUMN ] column_name DROP IDENTITY [ IF EXISTS ]
ADD AUTO_INCREMENT(column_name) [ =N ]
