EXPLAIN Statements

This documentation is for an out-of-date version of Apache Flink. We recommend you use the latest stable version.

EXPLAIN Statements #

EXPLAIN statements are used to explain the logical and optimized query plans of a query or an INSERT statement.

Run an EXPLAIN statement #

Java

EXPLAIN statements can be executed with the executeSql() method of the TableEnvironment. The executeSql() method returns explain result for a successful EXPLAIN operation, otherwise will throw an exception.

The following examples show how to run an EXPLAIN statement in TableEnvironment.

Scala

The following examples show how to run an EXPLAIN statement in TableEnvironment.

Python

EXPLAIN statements can be executed with the execute_sql() method of the TableEnvironment. The execute_sql() method returns explain result for a successful EXPLAIN operation, otherwise will throw an exception.

The following examples show how to run an EXPLAIN statement in TableEnvironment.

SQL CLI

EXPLAIN statements can be executed in SQL CLI.

The following examples show how to run an EXPLAIN statement in SQL CLI.

Java

StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);

// register a table named "Orders"
tEnv.executeSql("CREATE TABLE MyTable1 (`count` bigint, word VARCHAR(256) WITH (...)");
tEnv.executeSql("CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256) WITH (...)");

// explain SELECT statement through TableEnvironment.explainSql()
String explanation = tEnv.explainSql(
  "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' " +
  "UNION ALL " + 
  "SELECT `count`, word FROM MyTable2");
System.out.println(explanation);

// explain SELECT statement through TableEnvironment.executeSql()
TableResult tableResult = tEnv.executeSql(
  "EXPLAIN PLAN FOR " + 
  "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' " +
  "UNION ALL " + 
  "SELECT `count`, word FROM MyTable2");
tableResult.print();

Scala

val env = StreamExecutionEnvironment.getExecutionEnvironment()
val tEnv = StreamTableEnvironment.create(env)

// register a table named "Orders"
tEnv.executeSql("CREATE TABLE MyTable1 (`count` bigint, word VARCHAR(256) WITH (...)")
tEnv.executeSql("CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256) WITH (...)")

// explain SELECT statement through TableEnvironment.explainSql()
val explanation = tEnv.explainSql(
  "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' " +
  "UNION ALL " + 
  "SELECT `count`, word FROM MyTable2")
println(explanation)

// explain SELECT statement through TableEnvironment.executeSql()
val tableResult = tEnv.executeSql(
  "EXPLAIN PLAN FOR " + 
  "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' " +
  "UNION ALL " + 
  "SELECT `count`, word FROM MyTable2")
tableResult.print()

Python

settings = EnvironmentSettings.new_instance()...
table_env = StreamTableEnvironment.create(env, settings)

t_env.execute_sql("CREATE TABLE MyTable1 (`count` bigint, word VARCHAR(256) WITH (...)")
t_env.execute_sql("CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256) WITH (...)")

# explain SELECT statement through TableEnvironment.explain_sql()
explanation1 = t_env.explain_sql(
    "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' "
    "UNION ALL "
    "SELECT `count`, word FROM MyTable2")
print(explanation1)

# explain SELECT statement through TableEnvironment.execute_sql()
table_result = t_env.execute_sql(
    "EXPLAIN PLAN FOR "
    "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' "
    "UNION ALL "
    "SELECT `count`, word FROM MyTable2")
table_result.print()

SQL CLI

Flink SQL> CREATE TABLE MyTable1 (`count` bigint, word VARCHAR(256);
[INFO] Table has been created.

Flink SQL> CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256);
[INFO] Table has been created.

Flink SQL> EXPLAIN PLAN FOR SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' 
> UNION ALL 
> SELECT `count`, word FROM MyTable2;

The EXPLAIN result is:

Blink Planner

== Abstract Syntax Tree ==
LogicalUnion(all=[true])
  LogicalFilter(condition=[LIKE($1, _UTF-16LE'F%')])
    LogicalTableScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  LogicalTableScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])

== Optimized Physical Plan ==
Union(all=[true], union all=[count, word])
  Calc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')])
    TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])

== Optimized Execution Plan ==
Union(all=[true], union all=[count, word])
  Calc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')])
    TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])

Legacy Planner

== Abstract Syntax Tree ==
LogicalUnion(all=[true])
  LogicalFilter(condition=[LIKE($1, _UTF-16LE'F%')])
    FlinkLogicalTableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  FlinkLogicalTableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])

== Optimized Logical Plan ==
DataStreamUnion(all=[true], union all=[count, word])
  DataStreamCalc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')])
    TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])

== Physical Execution Plan ==
Stage 1 : Data Source
	content : collect elements with CollectionInputFormat

Stage 2 : Data Source
	content : collect elements with CollectionInputFormat

	Stage 3 : Operator
		content : from: (count, word)
		ship_strategy : REBALANCE

		Stage 4 : Operator
			content : where: (LIKE(word, _UTF-16LE'F%')), select: (count, word)
			ship_strategy : FORWARD

			Stage 5 : Operator
				content : from: (count, word)
				ship_strategy : REBALANCE

Syntax #

EXPLAIN PLAN FOR <query_statement_or_insert_statement>

For query syntax, please refer to Queries page. For INSERT, please refer to INSERT page.