运行 Describe 语句
— 焉知非鱼Run a Describe Statement
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