DESCRIBE 语句
- 执行 DESCRIBE 语句
- 语法

DESCRIBE 语句

DESCRIBE 语句用于描述表或视图的 schema，或catalog 的元数据，或 Flink 集群上的指定作业。

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() 方法会返回所有对象，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() 方法会返回所有对象，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() 方法会返回所有对象，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 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 (...)");
// 打印 schema
tableEnv.executeSql("DESCRIBE Orders").print();
// 打印 schema
tableEnv.executeSql("DESC Orders").print();
// 注册名为 “cat2” 的 catalog
tableEnv.executeSql("CREATE CATALOG cat2 WITH ('type'='generic_in_memory', 'default-database'='db')");
// 打印元数据
tableEnv.executeSql("DESCRIBE CATALOG cat2").print();
// 打印完整的元数据
tableEnv.executeSql("DESC CATALOG EXTENDED cat2").print();

Scala

val tableEnv = TableEnvironment.create(...)
// 注册名为 “Orders” 的表
 tableEnv.executeSql(
        "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 (...)")
// 打印 schema
tableEnv.executeSql("DESCRIBE Orders").print()
// 打印 schema
tableEnv.executeSql("DESC Orders").print()
// 注册名为 “cat2” 的 catalog
tableEnv.executeSql("CREATE CATALOG cat2 WITH ('type'='generic_in_memory', 'default-database'='db')")
// 打印元数据
tableEnv.executeSql("DESCRIBE CATALOG cat2").print()
// 打印完整的元数据
tableEnv.executeSql("DESC CATALOG EXTENDED cat2").print()

Python

table_env = TableEnvironment.create(...)
# 注册名为 “Orders” 的表
table_env.execute_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 (...)");
# 打印 schema
table_env.execute_sql("DESCRIBE Orders").print()
# 打印 schema
table_env.execute_sql("DESC Orders").print()
# 注册名为 “cat2” 的 catalog
table_env.execute_sql("CREATE CATALOG cat2 WITH ('type'='generic_in_memory', 'default-database'='db')")
# 打印元数据
table_env.execute_sql("DESCRIBE CATALOG cat2").print()
# 打印完整的元数据
table_env.execute_sql("DESC CATALOG EXTENDED cat2").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;
Flink SQL> CREATE CATALOG cat2 WITH ('type'='generic_in_memory', 'default-database'='db');
[INFO] Execute statement succeeded.
Flink SQL> DESCRIBE CATALOG cat2;
Flink SQL> DESC CATALOG EXTENDED cat2;
Flink SQL> DESCRIBE JOB '228d70913eab60dda85c5e7f78b5782c';
Flink SQL> DESC JOB '228d70913eab60dda85c5e7f78b5782c';

上述示例的结果是：

Java

# DESCRIBE TABLE Orders
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    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
# DESCRIBE CATALOG cat2
+-----------+-------------------+
| info name |        info value |
+-----------+-------------------+
|      name |              cat2 |
|      type | generic_in_memory |
|   comment |                   |
+-----------+-------------------+
3 rows in set
# DESCRIBE CATALOG EXTENDED cat2
+-------------------------+-------------------+
|               info name |        info value |
+-------------------------+-------------------+
|                    name |              cat2 |
|                    type | generic_in_memory |
|                 comment |                   |
| option:default-database |                db |
+-------------------------+-------------------+
4 rows in set

Scala

# DESCRIBE TABLE Orders
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    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
# DESCRIBE CATALOG cat2
+-----------+-------------------+
| info name |        info value |
+-----------+-------------------+
|      name |              cat2 |
|      type | generic_in_memory |
|   comment |                   |
+-----------+-------------------+
3 rows in set
# DESCRIBE CATALOG EXTENDED cat2
+-------------------------+-------------------+
|               info name |        info value |
+-------------------------+-------------------+
|                    name |              cat2 |
|                    type | generic_in_memory |
|                 comment |                   |
| option:default-database |                db |
+-------------------------+-------------------+
4 rows in set

Python

# DESCRIBE TABLE Orders
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    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
# DESCRIBE CATALOG cat2
+-----------+-------------------+
| info name |        info value |
+-----------+-------------------+
|      name |              cat2 |
|      type | generic_in_memory |
|   comment |                   |
+-----------+-------------------+
3 rows in set
# DESCRIBE CATALOG EXTENDED cat2
+-------------------------+-------------------+
|               info name |        info value |
+-------------------------+-------------------+
|                    name |              cat2 |
|                    type | generic_in_memory |
|                 comment |                   |
| option:default-database |                db |
+-------------------------+-------------------+
4 rows in set

SQL CLI

# DESCRIBE TABLE Orders
+---------+-----------------------------+-------+-----------+---------------+----------------------------+---------------------------+
|    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
# DESCRIBE CATALOG cat2
+-----------+-------------------+
| info name |        info value |
+-----------+-------------------+
|      name |              cat2 |
|      type | generic_in_memory |
|   comment |                   |
+-----------+-------------------+
3 rows in set
# DESCRIBE CATALOG EXTENDED cat2
+-------------------------+-------------------+
|               info name |        info value |
+-------------------------+-------------------+
|                    name |              cat2 |
|                    type | generic_in_memory |
|                 comment |                   |
| option:default-database |                db |
+-------------------------+-------------------+
4 rows in set
# DESCRIBE JOB '228d70913eab60dda85c5e7f78b5782c'
+----------------------------------+----------+---------+-------------------------+
|                           job id | job name |  status |              start time |
+----------------------------------+----------+---------+-------------------------+
| 228d70913eab60dda85c5e7f78b5782c |    myjob | RUNNING | 2023-02-11T05:03:51.523 |
+----------------------------------+----------+---------+-------------------------+
1 row in set

语法

DESCRIBE TABLE

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

DESCRIBE CATALOG

{ DESCRIBE | DESC } CATALOG [EXTENDED] catalog_name

DESCRIBE JOB

{ DESCRIBE | DESC } JOB '<job_id>'

Attention DESCRIBE JOB 语句仅适用于 SQL CLI 或者 SQL Gateway.