sql - 如何查看oracle数据库中一个表的所有列的元数据？

Question

我想知道允许我们查看为 oracle 数据库中的表定义的所有列的查询。

阐述:

表名:Some_Table 有 10 列。

我想知道如何检索所有列名、它们的数据类型以及为任何列定义的任何约束。

Answer 1

I want to know how I can retrieve the all column names, their data type, and any constraints that are defined for any column.

为此，您可以查询(取决于授予您的权限)[user|all|dba]_tab_columns, [user|all|dba]_cons_columns, [user|all|dba]_constraints View 。

这是一个简单的例子:

 select decode( t.table_name
              , lag(t.table_name, 1) over(order by t.table_name)
              , null
             , t.table_name ) as table_name -- <- just to eliminate 
      , t.column_name                       -- repeated tab_name    
      , t.data_type
      , cc.constraint_name
      , uc.constraint_type
   from user_tab_columns t
        left join user_cons_columns cc
          on (cc.table_name = t.table_name and
              cc.column_name = t.column_name)
        left join user_constraints uc
          on (t.table_name = uc.table_name and
              uc.constraint_name = cc.constraint_name )
 where t.table_name in ('EMPLOYEES', 'DEPARTMENTS');

结果:

TABLE_NAME    COLUMN_NAME       DATA_TYPE      CONSTRAINT_NAME   CONSTRAINT_TYPE
------------- ----------------- -------------- -------------------------------
DEPARTMENTS   LOCATION_ID       NUMBER         DEPT_LOC_FK       R
              DEPARTMENT_ID     NUMBER         DEPT_ID_PK        P
              DEPARTMENT_NAME   VARCHAR2       DEPT_NAME_NN      C
              MANAGER_ID        NUMBER         DEPT_MGR_FK       R
EMPLOYEES     SALARY            NUMBER         EMP_SALARY_MIN    C
              PHONE_NUMBER      VARCHAR2                            
              EMPLOYEE_ID       NUMBER         EMP_EMP_ID_PK     P
              DEPARTMENT_ID     NUMBER         EMP_DEPT_FK       R
              JOB_ID            VARCHAR2       EMP_JOB_FK        R
              MANAGER_ID        NUMBER         EMP_MANAGER_FK    R
              COMMISSION_PCT    NUMBER                              
              FIRST_NAME        VARCHAR2                            
              JOB_ID            VARCHAR2       EMP_JOB_NN        C
              HIRE_DATE         DATE           EMP_HIRE_DATE_NN  C
              EMAIL             VARCHAR2       EMP_EMAIL_NN      C
              LAST_NAME         VARCHAR2       EMP_LAST_NAME_NN  C
              EMAIL             VARCHAR2       EMP_EMAIL_UK      U

17 rows selected

还可以检索表的完整规范(如果需要)，您可以使用 dbms_metadata 包和该包的 get_ddl 函数:

select dbms_metadata.get_ddl('TABLE', 'EMPLOYEES') as table_ddl
  from dual;

 table_ddl
 --------------------------------------------------------------------------------

  CREATE TABLE "HR"."EMPLOYEES"
   ("EMPLOYEE_ID" NUMBER(6,0),
    "FIRST_NAME" VARCHAR2(20),
    "LAST_NAME" VARCHAR2(25) CONSTRAINT "EMP_LAST_NAME_NN" NOT NULL ENABLE,
    "EMAIL" VARCHAR2(25) CONSTRAINT "EMP_EMAIL_NN" NOT NULL ENABLE,
    "PHONE_NUMBER" VARCHAR2(20),
    "HIRE_DATE" DATE CONSTRAINT "EMP_HIRE_DATE_NN" NOT NULL ENABLE,
    "JOB_ID" VARCHAR2(10) CONSTRAINT "EMP_JOB_NN" NOT NULL ENABLE,
    "SALARY" NUMBER(8,2),
    "COMMISSION_PCT" NUMBER(2,2),
    "MANAGER_ID" NUMBER(6,0),
    "DEPARTMENT_ID" NUMBER(4,0),
     CONSTRAINT "EMP_SALARY_MIN" CHECK (salary > 0) ENABLE,
     CONSTRAINT "EMP_EMAIL_UK" UNIQUE ("EMAIL")

   -- ... other attributes

   )