如何通过 jdbc 运行命令“describe table_name”来查询 Oracle 数据库

Question

I know how to run normal select query.

        Class.forName("oracle.jdbc.driver.OracleDriver");
        String url = "jdbc:oracle:thin:@xxx";
        String uname = "";
        String passwd = "";
        Connection conn = DriverManager.getConnection(url, uname, passwd);
        Statement stmt = conn.createStatement();
        String sql = "select * from table_name";
        ResultSet rs = stmt.executeQuery(sql);
        while (rs.next()) {
            System.out.println();
        }

But how to run query like sql = "describe table_name" ?

Answer 1

describe is a SQL*Plus command; although it works elsewhere (such as in SQL Developer or TOAD), it is not a "standard" command so I don't think you can use it the way you wanted.

Therefore, as you already know how to run a "normal" query, do it again, but this time by fetching data from user_tab_columns which contains data you need. For example:

SQL> SELECT column_name, data_type, data_precision, data_length, nullable
  2  from user_tab_columns
  3  where table_name = 'TEMP';

COLUMN_NAME     DATA_TYPE       DATA_PRECISION DATA_LENGTH N
--------------- --------------- -------------- ----------- -
ID              NUMBER                                  22 Y
ENAME           VARCHAR2                                10 Y
JOB             VARCHAR2                                15 Y
DEPT            NUMBER                                  22 Y
HIREDATE        DATE                                     7 Y
LOC             VARCHAR2                                10 Y

6 rows selected.

which can be compared to

SQL> describe temp
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ID                                                 NUMBER
 ENAME                                              VARCHAR2(10)
 JOB                                                VARCHAR2(15)
 DEPT                                               NUMBER
 HIREDATE                                           DATE
 LOC                                                VARCHAR2(10)

SQL>

---

As of comments : there's that nice view named dictionary you can query and find some useful information, ie a system view which then lets you find another information. Here's how:

SQL> select * from dictionary
  2  where lower(table_name) like '%user%' and lower(comments) like '%comment%';

TABLE_NAME                COMMENTS
------------------------- --------------------------------------------------
USER_COL_COMMENTS         Comments on columns of user's tables and views
USER_INDEXTYPE_COMMENTS   Comments for user-defined indextypes
USER_MVIEW_COMMENTS       Comments on materialized views owned by the user
USER_OPERATOR_COMMENTS    Comments for user-defined operators
USER_TAB_COMMENTS         Comments on the tables and views owned by the user

OK; it is user_tab_comments and user_col_comments I need. So let's add some comments to the temp table:

SQL> comment on table temp is 'Sample table for Stack Overflow';

Comment created.

SQL> comment on column temp.ename is 'Employee''s name';

Comment created.

Result:

SQL> select * from user_tab_comments where table_name = 'TEMP';

TABLE_NAME                TABLE_TYPE  COMMENTS
------------------------- ----------- --------------------------------------------------
TEMP                      TABLE       Sample table for Stack Overflow

SQL> select * from user_col_comments where table_name = 'TEMP';

TABLE_NAME                COLUMN_NAME     COMMENTS
------------------------- --------------- --------------------------------------------------
TEMP                      ID
TEMP                      ENAME           Employee's name
TEMP                      JOB
TEMP                      DEPT
TEMP                      HIREDATE
TEMP                      LOC

6 rows selected.

SQL>