DESC actor;
-- 或
DESCRIBE actor;

Name         Null? Type
------------ ----- -------------
ACTOR_ID     NOT NULL NUMBER(5)
FIRST_NAME   NOT NULL VARCHAR2(45)
LAST_NAME    NOT NULL VARCHAR2(45)
LAST_UPDATE  NOT NULL DATE
CREATE_DATE  NOT NULL DATE

-- 查看指定表的所有列
SELECT 
    COLUMN_NAME,
    DATA_TYPE,
    DATA_LENGTH,
    NULLABLE,
    DATA_DEFAULT
FROM USER_TAB_COLUMNS 
WHERE TABLE_NAME = 'ACTOR'
ORDER BY COLUMN_ID;

SELECT 
    a.COLUMN_NAME,
    a.DATA_TYPE,
    a.DATA_LENGTH,
    a.NULLABLE,
    b.COMMENTS
FROM USER_TAB_COLUMNS a
LEFT JOIN USER_COL_COMMENTS b 
    ON a.TABLE_NAME = b.TABLE_NAME 
    AND a.COLUMN_NAME = b.COLUMN_NAME
WHERE a.TABLE_NAME = 'ACTOR'
ORDER BY a.COLUMN_ID;

-- 列信息 + 注釋
SELECT 
    t.COLUMN_ID,
    t.COLUMN_NAME,
    t.DATA_TYPE,
    t.DATA_LENGTH AS "LENGTH",
    t.NULLABLE,
    c.COMMENTS
FROM USER_TAB_COLUMNS t
LEFT JOIN USER_COL_COMMENTS c 
    ON t.TABLE_NAME = c.TABLE_NAME AND t.COLUMN_NAME = c.COLUMN_NAME
WHERE t.TABLE_NAME = UPPER('actor')
ORDER BY t.COLUMN_ID;

SELECT 
    a.COLUMN_NAME,
    a.CONSTRAINT_NAME
FROM USER_CONS_COLUMNS a
JOIN USER_CONSTRAINTS b 
    ON a.CONSTRAINT_NAME = b.CONSTRAINT_NAME
WHERE b.TABLE_NAME = 'ACTOR' 
    AND b.CONSTRAINT_TYPE = 'P';

-- Oracle 特有方式
SELECT DBMS_METADATA.GET_DDL('TABLE', 'ACTOR') FROM DUAL;

-- 如果表屬于其他用戶（如 SCOTT）
SELECT DBMS_METADATA.GET_DDL('TABLE', 'ACTOR', 'SCOTT') FROM DUAL;

CREATE TABLE "SCOTT"."ACTOR" (
   "ACTOR_ID"    NUMBER(5) NOT NULL ENABLE,
   "FIRST_NAME"  VARCHAR2(45) NOT NULL ENABLE,
   "LAST_NAME"   VARCHAR2(45) NOT NULL ENABLE,
   "LAST_UPDATE" DATE NOT NULL ENABLE,
   "CREATE_DATE" DATE DEFAULT TO_DATE('2020-10-01','YYYY-MM-DD') NOT NULL ENABLE,
   PRIMARY KEY ("ACTOR_ID") ENABLE
)