EXPLAIN 语句

EXPLAIN 语句用于解释一个查询或 INSERT 语句的逻辑和优化查询计划。

运行 EXPLAIN 语句 #

EXPLAIN 语句可以用 TableEnvironment 的 executeSql() 方法执行，也可以在 SQL CLI 中执行。executeSql() 方法在 EXPLAIN 操作成功后返回解释结果，否则将抛出一个异常。

下面的例子展示了如何在 TableEnvironment 和 SQL CLI 中运行 EXPLAIN 语句。

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

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

EXPLAIN 的结果是：

== 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>

关于查询语法，请参考查询页面。关于 INSERT，请参考 INSERT 页面。