Flink SQL 知其所以然：Explain、Show、Load、Set 子句

EXPLAIN 子句

大家好，我是老羊，今天我们来学习 Flink SQL 中的的 Explain、Show、Load、Set 共 4 个子句。

应用场景：EXPLAIN 子句其实就是用于查看当前这个 sql 查询的逻辑计划以及优化的执行计划。SQL 语法标准： 复制EXPLAIN PLAN FOR <query_statement_or_insert_statement>1. 实际案例： 复制public class Explain_Test { public static void main(String[] args) throws Exception { FlinkEnv flinkEnv = FlinkEnvUtils.getStreamTableEnv(args); flinkEnv.env().setParallelism(1); String sql = "CREATE TABLE source_table (\n" + " user_id BIGINT COMMENT 用户 id,\n" + " name STRING COMMENT 用户姓名,\n" + " server_timestamp BIGINT COMMENT 用户访问时间戳,\n" + " proctime AS PROCTIME()\n" + ") WITH (\n" + " connector = datagen,\n" + " rows-per-second = 1,\n" + " fields.name.length = 1,\n" + " fields.user_id.min = 1,\n" + " fields.user_id.max = 10,\n" + " fields.server_timestamp.min = 1,\n" + " fields.server_timestamp.max = 100000\n" + ");\n" + "\n" + "CREATE TABLE sink_table (\n" + " user_id BIGINT,\n" + " name STRING,\n" + " server_timestamp BIGINT\n" + ") WITH (\n" + " connector = print\n" + ");\n" + "\n" + "EXPLAIN PLAN FOR\n" + "INSERT INTO sink_table\n" + "select user_id,\n" + " name,\n" + " server_timestamp\n" + "from (\n" + " SELECT\n" + " user_id,\n" + " name,\n" + " server_timestamp,\n" + " row_number() over(partition by user_id order by proctime) as rn\n" + " FROM source_table\n" + ")\n" + "where rn = 1"; /** * 算子 {@link org.apache.flink.streaming.api.operators.KeyedProcessOperator} * -- {@link org.apache.flink.table.runtime.operators.deduplicate.ProcTimeDeduplicateKeepFirstRowFunction} */ for (String innerSql : sql.split(";")) { TableResult tableResult = flinkEnv.streamTEnv().executeSql(innerSql); tableResult.print(); } }}1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.39.40.41.42.43.44.45.46.47.48.49.50.51.

上述代码执行结果如下：

复制1

. 抽象语法树

== Abstract Syntax Tree ==LogicalSink(table=[default_catalog.default_database.sink_table], fields=[user_id, name, server_timestamp])+- LogicalProject(user_id=[$0], name=[$1], server_timestamp=[$2]) +- LogicalFilter(condition=[=($3, 1)]) +- LogicalProject(user_id=[$0], name=[$1], server_timestamp=[$2], rn=[ROW_NUMBER() OVER (PARTITION BY $0 ORDER BY PROCTIME() NULLS FIRST)]) +- LogicalTableScan(table=[[default_catalog, default_database, source_table]])2

. 优化后的物理计划

== Optimized Physical Plan ==Sink(table=[default_catalog.default_database.sink_table], fields=[user_id, name, server_timestamp])+- Calc(select=[user_id, name, server_timestamp]) +- Deduplicate(keep=[FirstRow], key=[user_id], order=[PROCTIME]) +- Exchange(distribution=[hash[user_id]]) +- Calc(select=[user_id, name, server_timestamp, PROCTIME() AS $3]) +- TableSourceScan(table=[[default_catalog, default_database, source_table]], fields=[user_id, name, server_timestamp])3

. 优化后的执行计划

== Optimized Execution Plan ==Sink(table=[default_catalog.default_database.sink_table], fields=[user_id, name, server_timestamp])+- Calc(select=[user_id, name, server_timestamp]) +- Deduplicate(keep=[FirstRow], key=[user_id], order=[PROCTIME]) +- Exchange(distribution=[hash[user_id]]) +- Calc(select=[user_id, name, server_timestamp, PROCTIME() AS $3]) +- TableSourceScan(table=[[default_catalog, default_database, source_table]], fields=[user_id, name, server_timestamp])1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.

USE 子句

应用场景：如果熟悉 MySQL 的同学会非常熟悉这个子句，在 MySQL 中，USE 子句通常被用于切换库，那么在 Flink SQL 体系中，它的源码库作用也是和 MySQL 中 USE 子句的功能基本一致，用于切换 Catalog，DataBase，使用 Module。SQL 语法标准：切换 Catalog： 复制USE CATALOG catalog_name1. 使用 Module： 复制USE MODULES module_name1[, module_name2, ...]1. 切换 Database： 复制USE db名称1. 实际案例： 复制StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);// create

a catalog

tEnv.executeSql("CREATE CATALOG cat1 WITH (...)");tEnv.executeSql("SHOW CATALOGS").print();// +-----------------+// | catalog name |// +-----------------+// | default_catalog |// | cat1 |// +-----------------+//

change default catalog

tEnv.executeSql("USE CATALOG cat1");tEnv.executeSql("SHOW DATABASES").print();//

databases are empty

// +---------------+// | database name |// +---------------+// +---------------+// create

a database

tEnv.executeSql("CREATE DATABASE db1 WITH (...)");tEnv.executeSql("SHOW DATABASES").print();// +---------------+// | database name |// +---------------+// | db1 |// +---------------+//

change default database

tEnv.executeSql("USE db1");// change module resolution order and

enabled status

tEnv.executeSql("USE MODULES hive");tEnv.executeSql("SHOW FULL MODULES").print();// +-------------+-------+// | module name | used |// +-------------+-------+// | hive | true |// | core | false |// +-------------+-------+1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.

SHOW 子句

应用场景：如果熟悉 MySQL 的同学会非常熟悉这个子句，在 MySQL 中，SHOW 子句常常用于查询库、表、函数等，在 Flink SQL 体系中也类似。Flink SQL 支持 SHOW 以下内容。SQL 语法标准：

复制SHOW CATALOGS：展示所有 Catalog

SHOW CURRENT CATALOG：展示当前的 Catalog

SHOW DATABASES：展示当前 Catalog 下所有 Database

SHOW CURRENT DATABASE：展示当前的 Database

SHOW TABLES：展示当前 Database 下所有表

SHOW VIEWS：展示所有视图

SHOW FUNCTIONS：展示所有的函数

SHOW MODULES：展示所有的 Module（Module 是用于 UDF 扩展）1.2.3.4.5.6.7.8. 实际案例： 复制StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);//

show catalogs

tEnv.executeSql("SHOW CATALOGS").print();// +-----------------+// | catalog name |// +-----------------+// | default_catalog |// +-----------------+//

show current catalog

tEnv.executeSql("SHOW CURRENT CATALOG").print();// +----------------------+// | current catalog name |// +----------------------+// | default_catalog |// +----------------------+//

show databases

tEnv.executeSql("SHOW DATABASES").print();// +------------------+// | database name |// +------------------+// | default_database |// +------------------+//

show current database

tEnv.executeSql("SHOW CURRENT DATABASE").print();// +-----------------------+// | current database name |// +-----------------------+// | default_database |// +-----------------------+// create a tabletEnv.executeSql("CREATE TABLE my_table (...) WITH (...)");//

show tables

tEnv.executeSql("SHOW TABLES").print();// +------------+// | table name |// +------------+// | my_table |// +------------+// create

a view

tEnv.executeSql("CREATE VIEW my_view AS ...");//

show views

tEnv.executeSql("SHOW VIEWS").print();// +-----------+// | view name |// +-----------+// | my_view |// +-----------+//

show functions

tEnv.executeSql("SHOW FUNCTIONS").print();// +---------------+// | function name |// +---------------+// | mod |// | sha256 |// | ... |// +---------------+// create

a user defined function

tEnv.executeSql("CREATE FUNCTION f1 AS ...");//

show user defined functions

tEnv.executeSql("SHOW USER FUNCTIONS").print();// +---------------+// | function name |// +---------------+// | f1 |// | ... |// +---------------+//

show modules

tEnv.executeSql("SHOW MODULES").print();// +-------------+// | module name |// +-------------+// | core |// +-------------+//

show full modules

tEnv.executeSql("SHOW FULL MODULES").print();// +-------------+-------+// | module name | used |// +-------------+-------+// | core | true |// | hive | false |// +-------------+-------+1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.32.33.34.35.36.37.38.39.40.41.42.43.44.45.46.47.48.49.50.51.52.53.54.55.56.57.58.59.60.61.62.63.64.65.66.67.68.69.70.71.72.73.74.75.76.77.78.79.80.81.82.

LOAD、亿华云UNLOAD 子句

应用场景：我们可以使用 LOAD 子句去加载 Flink SQL 体系内置的或者用户自定义的 Module，UNLOAD 子句去卸载 Flink SQL 体系内置的或者用户自定义的 Module。SQL 语法标准： 复制-- 加载LOAD MODULE module_name [WITH (key1 = val1, key2 = val2, ...)]-- 卸载UNLOAD MODULE module_name1.2.3.4. 实际案例：LOAD 案例： 复制StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);//

加载 Flink SQL 体系内置的 Hive module

tEnv.executeSql("LOAD MODULE hive WITH (hive-version = 3.1.2)");tEnv.executeSql("SHOW MODULES").print();// +-------------+// | module name |// +-------------+// | core |// | hive |// +-------------+1.2.3.4.5.6.7.8.9.10.11. UNLOAD 案例： 复制StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);//

卸载唯一的一个 CoreModule

tEnv.executeSql("UNLOAD MODULE core");tEnv.executeSql("SHOW MODULES").print();// 结果啥 Moudle 都没有了1.2.3.4.5.6.

SET、RESET 子句

应用场景：SET 子句可以用于修改一些 Flink SQL 的环境配置，RESET 子句是可以将所有的环境配置恢复成默认配置，但只能在 SQL CLI 中进行使用，主要是为了让用户更纯粹的使用 SQL 而不必使用其他方式或者切换系统环境。SQL 语法标准： 复制SET (key = value)?RESET (key)?1.2. 实际案例：

启动一个 SQL CLI 之后，在 SQL CLI 中可以进行以下 SET 设置：

复制Flink SQL> SET table.planner = blink;[INFO] Session property has been set

.

Flink SQL> SET;table.planner=blink;Flink SQL> RESET table.planner;[INFO]

Session property has been reset.

Flink SQL> RESET;[INFO] All session properties have been set to their default values.1.2.3.4.5.6.7.8.云服务器

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