DESCRIBE 语句
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DESCRIBE 语句 #

DESCRIBE 语句用于描述表或视图的 schema 或 catalog 的元数据。

执行 DESCRIBE 语句 #

可以使用 TableEnvironmentexecuteSql() 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。

可以使用 TableEnvironmentexecuteSql() 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。

可以使用 TableEnvironmentexecute_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。

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。

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();
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()
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()
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;

上述示例的结果是:

# 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 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 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 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

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语法 #

  • DESCRIBE TABLE
{ DESCRIBE | DESC } [catalog_name.][db_name.]table_name
  • DESCRIBE CATALOG
{ DESCRIBE | DESC } CATALOG [EXTENDED] catalog_name