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，也可以在 SQL CLI 中执行 EXPLAIN 语句。 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 和 SQL CLI 中执行一条 EXPLAIN 语句。

  1. StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
  2. StreamTableEnvironment tEnv = StreamTableEnvironment.create(env);
  4. // register a table named "Orders"
  5. tEnv.executeSql("CREATE TABLE MyTable1 (count bigint, work VARCHAR(256) WITH (...)");
  6. tEnv.executeSql("CREATE TABLE MyTable2 (count bigint, work VARCHAR(256) WITH (...)");
  8. // explain SELECT statement through TableEnvironment.explainSql()
  9. String explanation = tEnv.explainSql(
  10.   "SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' " +
  11.   "UNION ALL " + 
  12.   "SELECT count, word FROM MyTable2");
  13. System.out.println(explanation);
  15. // explain SELECT statement through TableEnvironment.executeSql()
  16. TableResult tableResult = tEnv.executeSql(
  17.   "EXPLAIN PLAN FOR " + 
  18.   "SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' " +
  19.   "UNION ALL " + 
  20.   "SELECT count, word FROM MyTable2");
  21. tableResult.print();
  1. val env = StreamExecutionEnvironment.getExecutionEnvironment()
  2. val tEnv = StreamTableEnvironment.create(env)
  4. // register a table named "Orders"
  5. tEnv.executeSql("CREATE TABLE MyTable1 (count bigint, work VARCHAR(256) WITH (...)")
  6. tEnv.executeSql("CREATE TABLE MyTable2 (count bigint, work VARCHAR(256) WITH (...)")
  8. // explain SELECT statement through TableEnvironment.explainSql()
  9. val explanation = tEnv.explainSql(
  10.   "SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' " +
  11.   "UNION ALL " + 
  12.   "SELECT count, word FROM MyTable2")
  13. println(explanation)
  15. // explain SELECT statement through TableEnvironment.executeSql()
  16. val tableResult = tEnv.executeSql(
  17.   "EXPLAIN PLAN FOR " + 
  18.   "SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' " +
  19.   "UNION ALL " + 
  20.   "SELECT count, word FROM MyTable2")
  21. tableResult.print()
  1. settings = EnvironmentSettings.new_instance()...
  2. table_env = StreamTableEnvironment.create(env, settings)
  4. t_env.execute_sql("CREATE TABLE MyTable1 (count bigint, work VARCHAR(256) WITH (...)")
  5. t_env.execute_sql("CREATE TABLE MyTable2 (count bigint, work VARCHAR(256) WITH (...)")
  7. # explain SELECT statement through TableEnvironment.explain_sql()
  8. explanation1 = t_env.explain_sql(
  9.     "SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' "
  10.     "UNION ALL "
  11.     "SELECT count, word FROM MyTable2")
  12. print(explanation1)
  14. # explain SELECT statement through TableEnvironment.execute_sql()
  15. table_result = t_env.execute_sql(
  16.     "EXPLAIN PLAN FOR "
  17.     "SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' "
  18.     "UNION ALL "
  19.     "SELECT count, word FROM MyTable2")
  20. table_result.print()
  1. Flink SQL> CREATE TABLE MyTable1 (count bigint, work VARCHAR(256);
  2. [INFO] Table has been created.
  4. Flink SQL> CREATE TABLE MyTable2 (count bigint, work VARCHAR(256);
  5. [INFO] Table has been created.
  7. Flink SQL> EXPLAIN PLAN FOR SELECT count, word FROM MyTable1 WHERE word LIKE 'F%' 
  8. > UNION ALL 
  9. > SELECT count, word FROM MyTable2;

执行 EXPLAIN 语句后的结果为：

  1. == Abstract Syntax Tree ==
  2. LogicalUnion(all=[true])
  3.   LogicalFilter(condition=[LIKE($1, _UTF-16LE'F%')])
  4.     FlinkLogicalTableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  5.   FlinkLogicalTableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])
  8. == Optimized Logical Plan ==
  9. DataStreamUnion(all=[true], union all=[count, word])
  10.   DataStreamCalc(select=[count, word], where=[LIKE(word, _UTF-16LE'F%')])
  11.     TableSourceScan(table=[[default_catalog, default_database, MyTable1]], fields=[count, word])
  12.   TableSourceScan(table=[[default_catalog, default_database, MyTable2]], fields=[count, word])
  14. == Physical Execution Plan ==
  15. Stage 1 : Data Source
  16.     content : collect elements with CollectionInputFormat
  18. Stage 2 : Data Source
  19.     content : collect elements with CollectionInputFormat
  21.     Stage 3 : Operator
  22.         content : from: (count, word)
  23.         ship_strategy : REBALANCE
  25.         Stage 4 : Operator
  26.             content : where: (LIKE(word, _UTF-16LE'F%')), select: (count, word)
  27.             ship_strategy : FORWARD
  29.             Stage 5 : Operator
  30.                 content : from: (count, word)
  31.                 ship_strategy : REBALANCE

语法

  1. 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。