DESCRIBE 语句

DESCRIBE 语句用于描述表或视图的模式。

运行一个DESCRIBE语句 #

DESCRIBE语句可以用TableEnvironment的executeSql()方法执行，也可以在SQL CLI中执行。executeSql()方法对于一个成功的DESCRIBE操作会返回给定表的模式，否则会抛出一个异常。

下面的例子展示了如何在TableEnvironment和SQL CLI中运行DESCRIBE语句。

val settings = EnvironmentSettings.newInstance()...
val tableEnv = TableEnvironment.create(settings)

// register a table named "Orders"
 tableEnv.executeSql(
        "CREATE TABLE Orders (" +
        " `user` BIGINT NOT NULl," +
        " product VARCHAR(32)," +
        " amount INT," +
        " ts TIMESTAMP(3)," +
        " ptime AS PROCTIME()," +
        " PRIMARY KEY(`user`) NOT ENFORCED," +
        " WATERMARK FOR ts AS ts - INTERVAL '1' SECONDS" +
        ") with (...)")

// print the schema
tableEnv.executeSql("DESCRIBE Orders").print()

Flink SQL> CREATE TABLE Orders (
>  `user` BIGINT NOT NULl,
>  product VARCHAR(32),
>  amount INT,
>  ts TIMESTAMP(3),
>  ptime AS PROCTIME(),
>  PRIMARY KEY(`user`) NOT ENFORCED,
>  WATERMARK FOR ts AS ts - INTERVAL '1' SECONDS
> ) with (
>  ...
> );
[INFO] Table has been created.

Flink SQL> DESCRIBE Orders;

root
 |-- user: BIGINT NOT NULL
 |-- product: VARCHAR(32)
 |-- amount: INT
 |-- ts: TIMESTAMP(3) *ROWTIME*
 |-- ptime: TIMESTAMP(3) NOT NULL *PROCTIME* AS PROCTIME()
 |-- WATERMARK FOR ts AS `ts` - INTERVAL '1' SECOND
 |-- CONSTRAINT PK_3599338 PRIMARY KEY (user)

上述例子的结果是：

+---------+----------------------------------+-------+-----------+-----------------+----------------------------+
|    name |                             type |  null |       key | computed column |                  watermark |
+---------+----------------------------------+-------+-----------+-----------------+----------------------------+
|    user |                           BIGINT | false | PRI(user) |                 |                            |
| product |                      VARCHAR(32) |  true |           |                 |                            |
|  amount |                              INT |  true |           |                 |                            |
|      ts |           TIMESTAMP(3) *ROWTIME* |  true |           |                 | `ts` - INTERVAL '1' SECOND |
|   ptime | TIMESTAMP(3) NOT NULL *PROCTIME* | false |           |      PROCTIME() |                            |
+---------+----------------------------------+-------+-----------+-----------------+----------------------------+
5 rows in set

语法 #

DESCRIBE [catalog_name.][db_name.]table_name

原文链接: https://ci.apache.org/projects/flink/flink-docs-release-1.11/dev/table/sql/describe.html