DESCRIBE 语句

DESCRIBE 语句用于描述表或视图的 schema。

执行 DESCRIBE 语句

Java

可以使用 TableEnvironment 的 executeSql() 方法执行 DESCRIBE 语句。如果 DESCRIBE 操作执行成功，executeSql() 方法会返回给定表的 schema，否则会抛出异常。

以下示例展示了如何在 TableEnvironment 中执行一条 DESCRIBE 语句。

Scala

可以使用 TableEnvironment 的 executeSql() 方法执行 DESCRIBE 语句。如果 DESCRIBE 操作执行成功，executeSql() 方法会返回给定表的 schema，否则会抛出异常。

以下示例展示了如何在 TableEnvironment 中执行一条 DESCRIBE 语句。

Python

可以使用 TableEnvironment 的 execute_sql() 方法执行 DESCRIBE 语句。如果 DESCRIBE 操作执行成功，execute_sql() 方法会返回给定表的 schema，否则会抛出异常。

以下示例展示了如何在 TableEnvironment 中执行一条 DESCRIBE 语句。

SQL CLI

DESCRIBE 语句可以在 SQL CLI 中执行。

以下示例展示了如何在 SQL CLI 中执行一条 DESCRIBE 语句。

Java

TableEnvironment tableEnv = TableEnvironment.create(...);
// 注册名为 “Orders” 的表
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 (...)");
// 打印 schema
tableEnv.executeSql("DESCRIBE Orders").print();
// 打印 schema
tableEnv.executeSql("DESC Orders").print();

Scala

val tableEnv = TableEnvironment.create(...)
// 注册名为 “Orders” 的表
 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 (...)")
// 打印 schema
tableEnv.executeSql("DESCRIBE Orders").print()
// 打印 schema
tableEnv.executeSql("DESC Orders").print()

Python

table_env = TableEnvironment.create(...)
# 注册名为 “Orders” 的表
table_env.execute_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 (...)");
# 打印 schema
table_env.execute_sql("DESCRIBE Orders").print()
# 打印 schema
table_env.execute_sql("DESC Orders").print()

SQL CLI

Flink SQL> CREATE TABLE Orders (
>  `user` BIGINT NOT NULl comment 'this is primary key',
>  product VARCHAR(32),
>  amount INT,
>  ts TIMESTAMP(3) comment 'notice: watermark',
>  ptime AS PROCTIME() comment 'this is a computed column',
>  PRIMARY KEY(`user`) NOT ENFORCED,
>  WATERMARK FOR ts AS ts - INTERVAL '1' SECONDS
> ) with (
>  ...
> );
[INFO] Table has been created.
Flink SQL> DESCRIBE Orders;
Flink SQL> DESC Orders;

上述示例的结果是：

Java

+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    name |                        type |  null |       key |        extras |                  watermark |                   comment |
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    user |                      BIGINT | FALSE | PRI(user) |               |                            |       this is primary key |
| product |                 VARCHAR(32) |  TRUE |           |               |                            |                           |
|  amount |                         INT |  TRUE |           |               |                            |                           |
|      ts |      TIMESTAMP(3) *ROWTIME* |  TRUE |           |               | `ts` - INTERVAL '1' SECOND |         notice: watermark |
|   ptime | TIMESTAMP_LTZ(3) *PROCTIME* | FALSE |           | AS PROCTIME() |                            | this is a computed column |
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
5 rows in set

Scala

+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    name |                        type |  null |       key |        extras |                  watermark |                   comment |
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    user |                      BIGINT | FALSE | PRI(user) |               |                            |       this is primary key |
| product |                 VARCHAR(32) |  TRUE |           |               |                            |                           |
|  amount |                         INT |  TRUE |           |               |                            |                           |
|      ts |      TIMESTAMP(3) *ROWTIME* |  TRUE |           |               | `ts` - INTERVAL '1' SECOND |         notice: watermark |
|   ptime | TIMESTAMP_LTZ(3) *PROCTIME* | FALSE |           | AS PROCTIME() |                            | this is a computed column |
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
5 rows in set

Python

+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    name |                        type |  null |       key |        extras |                  watermark |                   comment |
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    user |                      BIGINT | FALSE | PRI(user) |               |                            |       this is primary key |
| product |                 VARCHAR(32) |  TRUE |           |               |                            |                           |
|  amount |                         INT |  TRUE |           |               |                            |                           |
|      ts |      TIMESTAMP(3) *ROWTIME* |  TRUE |           |               | `ts` - INTERVAL '1' SECOND |         notice: watermark |
|   ptime | TIMESTAMP_LTZ(3) *PROCTIME* | FALSE |           | AS PROCTIME() |                            | this is a computed column |
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
5 rows in set

SQL CLI

root
 |-- user: BIGINT NOT NULL COMMENT 'this is primary key'
 |-- product: VARCHAR(32)
 |-- amount: INT
 |-- ts: TIMESTAMP(3) *ROWTIME* COMMENT 'notice: watermark'
 |-- ptime: TIMESTAMP(3) NOT NULL *PROCTIME* AS PROCTIME() COMMENT 'this is a computed column'
 |-- WATERMARK FOR ts AS `ts` - INTERVAL '1' SECOND
 |-- CONSTRAINT PK_3599338 PRIMARY KEY (user)

语法

{ DESCRIBE | DESC } [catalog_name.][db_name.]table_name