EXPLAIN 语句

EXPLAIN 语句用来解释一条 query 语句或者 INSERT 语句的逻辑计划和优化后的计划。

运行一条 EXPLAIN 语句

EXPLAIN 语句可以通过 TableEnvironment 的 executeSql() 执行。 若 EXPLAIN 操作执行成功，executeSql() 方法返回解释的结果，否则会抛出异常。

以下的例子展示了如何在 TableEnvironment 中执行一条 EXPLAIN 语句。

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();

执行 EXPLAIN 语句后的结果为：

== 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

语法

EXPLAIN PLAN FOR <query_statement_or_insert_statement>

请参阅 Queries 页面获得 query 的语法。 请参阅 INSERT 页面获得 INSERT 的语法。