EXPLAIN 语句
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EXPLAIN 语句 #

EXPLAIN 语句用于解释 query 或 INSERT 语句的执行逻辑，也用于优化 query 语句的查询计划。

执行 EXPLAIN 语句 #

可以使用 TableEnvironment 的 executeSql() 方法执行 EXPLAIN 语句。如果 EXPLAIN 操作执行成功，executeSql() 方法会返回解释结果，否则会抛出异常。

以下示例展示了如何在 TableEnvironment 中执行一条 EXPLAIN 语句。

可以使用 TableEnvironment 的 executeSql() 方法执行 EXPLAIN 语句。如果 EXPLAIN 操作执行成功，executeSql() 方法会返回解释结果，否则会抛出异常。

以下示例展示了如何在 TableEnvironment 中执行一条 EXPLAIN 语句。

可以使用 TableEnvironment 的 execute_sql() 方法执行 EXPLAIN 语句。如果 EXPLAIN 操作执行成功，execute_sql() 方法会返回解释结果，否则会抛出异常。

以下示例展示了如何在 TableEnvironment 中执行一条 EXPLAIN 语句。

EXPLAIN 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 EXPLAIN 语句。

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

// 注册名为 “Orders” 的表
tEnv.executeSql("CREATE TABLE MyTable1 (`count` bigint, word VARCHAR(256)) WITH ('connector' = 'datagen')");
tEnv.executeSql("CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256)) WITH ('connector' = 'datagen')");

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

// 调用 TableEnvironment.executeSql() 来解释 SELECT 语句
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();

TableResult tableResult2 = tEnv.executeSql(
  "EXPLAIN ESTIMATED_COST, CHANGELOG_MODE, JSON_EXECUTION_PLAN " + 
  "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' " +
  "UNION ALL " + 
  "SELECT `count`, word FROM MyTable2");
tableResult2.print();

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

// 注册名为 “Orders” 的表
tEnv.executeSql("CREATE TABLE MyTable1 (`count` bigint, word VARCHAR(256)) WITH ('connector' = 'datagen')")
tEnv.executeSql("CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256)) WITH ('connector' = 'datagen')")

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

// 调用 TableEnvironment.executeSql() 来解释 SELECT 语句
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()

val tableResult2 = tEnv.executeSql(
  "EXPLAIN ESTIMATED_COST, CHANGELOG_MODE, JSON_EXECUTION_PLAN " + 
  "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' " +
  "UNION ALL " + 
  "SELECT `count`, word FROM MyTable2")
tableResult2.print()

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

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

# 调用 TableEnvironment.explain_sql() 来解释 SELECT 语句
explanation1 = t_env.explain_sql(
    "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' "
    "UNION ALL "
    "SELECT `count`, word FROM MyTable2")
print(explanation1)

# 调用 TableEnvironment.execute_sql() 来解释 SELECT 语句
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()

table_result2 = t_env.execute_sql(
    "EXPLAIN ESTIMATED_COST, CHANGELOG_MODE, JSON_EXECUTION_PLAN "
    "SELECT `count`, word FROM MyTable1 WHERE word LIKE 'F%' "
    "UNION ALL "
    "SELECT `count`, word FROM MyTable2")
table_result2.print()

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

Flink SQL> CREATE TABLE MyTable2 (`count` bigint, word VARCHAR(256)) WITH ('connector' = 'datagen');
[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;
                                  
Flink SQL> EXPLAIN ESTIMATED_COST, CHANGELOG_MODE, JSON_EXECUTION_PLAN SELECT `count`, word FROM MyTable1 
> WHERE word LIKE 'F%' 
> UNION ALL 
> SELECT `count`, word FROM MyTable2;

EXPLAIN 的结果如下:

== Abstract Syntax Tree ==
LogicalUnion(all=[true])
:- LogicalProject(count=[$0], word=[$1])
:  +- LogicalFilter(condition=[LIKE($1, _UTF-16LE'F%')])
:     +- LogicalTableScan(table=[[default_catalog, default_database, MyTable1]])
+- LogicalProject(count=[$0], word=[$1])
   +- LogicalTableScan(table=[[default_catalog, default_database, MyTable2]])

== Optimized Physical Plan ==
Union(all=[true], union=[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=[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])

== Abstract Syntax Tree ==
LogicalUnion(all=[true])
:- LogicalProject(count=[$0], word=[$1])
:  +- LogicalFilter(condition=[LIKE($1, _UTF-16LE'F%')])
:     +- LogicalTableScan(table=[[default_catalog, default_database, MyTable1]])
+- LogicalProject(count=[$0], word=[$1])
   +- LogicalTableScan(table=[[default_catalog, default_database, MyTable2]])

== Optimized Physical Plan ==
Union(all=[true], union=[count, word], changelogMode=[I]): rowcount = 1.05E8, cumulative cost = {3.1E8 rows, 3.05E8 cpu, 4.0E9 io, 0.0 network, 0.0 memory}
:- Calc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')], changelogMode=[I]): rowcount = 5000000.0, cumulative cost = {1.05E8 rows, 1.0E8 cpu, 2.0E9 io, 0.0 network, 0.0 memory}
:  +- TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word], changelogMode=[I]): rowcount = 1.0E8, cumulative cost = {1.0E8 rows, 1.0E8 cpu, 2.0E9 io, 0.0 network, 0.0 memory}
+- TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word], changelogMode=[I]): rowcount = 1.0E8, cumulative cost = {1.0E8 rows, 1.0E8 cpu, 2.0E9 io, 0.0 network, 0.0 memory}

== Optimized Execution Plan ==
Union(all=[true], union=[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])

== Physical Execution Plan ==
{
  "nodes" : [ {
    "id" : 37,
    "type" : "Source: TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])",
    "pact" : "Data Source",
    "contents" : "Source: TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])",
    "parallelism" : 1
  }, {
    "id" : 38,
    "type" : "Calc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')])",
    "pact" : "Operator",
    "contents" : "Calc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')])",
    "parallelism" : 1,
    "predecessors" : [ {
      "id" : 37,
      "ship_strategy" : "FORWARD",
      "side" : "second"
    } ]
  }, {
    "id" : 39,
    "type" : "Source: TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])",
    "pact" : "Data Source",
    "contents" : "Source: TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])",
    "parallelism" : 1
  } ]

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ExplainDetails # 

使用指定的 explainDetail 类型来打印语句的计划。

ESTIMATED_COST：生成优化器（optimizer）估算的物理节点相关的成本信息, 
例如：TableSourceScan(..., cumulative cost ={1.0E8 rows, 1.0E8 cpu, 2.4E9 io, 0.0 network, 0.0 memory})

CHANGELOG_MODE：为每个物理 RelNode 生成 changelog mode。
例如：GroupAggregate(..., changelogMode=[I,UA,D])

JSON_EXECUTION_PLAN：生成 json 格式的程序执行计划。

语法 # 

EXPLAIN [([ExplainDetail[, ExplainDetail]*]) | PLAN FOR] <query_statement_or_insert_statement_or_statement_set>

statement_set:
EXECUTE STATEMENT SET
BEGIN
insert_statement;
...
insert_statement;
END;

关于 query 的语法，请查阅 Queries 页面。 关于 INSERT 的语法，请查阅 INSERT 页面。