概览

查询 #

TableEnvironment 的 sqlQuery() 方法可以执行 SELECT 和 VALUES 语句。 这个方法把 SELECT 语句(或 VALUES 语句)的结果作为一个 Table 返回。 Table可以用在后续 SQL 和 Table API 查询中，可以转换为 DataStream， 或者 写入到TableSink。 SQL 和 Table API 查询可以无缝混合，并进行整体优化并转换为单个程序。

为了在SQL查询中访问表，它必须注册在 TableEnvironment。 表使用下列方式注册：TableSource， Table，CREATE TABLE 语句，DataStream。 也可以通过在 TableEnvironment 中注册 Catalog 来指定数据源的位置。

为了方便起见，Table.toString() 自动在 TableEnvironment 中注册一个名称唯一的表，并返回表名。 所以Table对象可以直接内嵌入 SQL 中查询使用，如下示例所示。

注意: 查询如果包含不支持的 SQL 特性，会抛出TableException异常。 下面的章节中列出了批处理和流处理上支持的 SQL 特性。

指定查询 #

下面的示例演示如何在一个注册的表和内联(inlined)的表上指定SQL查询。

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

// ingest a DataStream from an external source
DataStream<Tuple3<Long, String, Integer>> ds = env.addSource(...);

// SQL query with an inlined (unregistered) table
Table table = tableEnv.fromDataStream(ds, $("user"), $("product"), $("amount"));
Table result = tableEnv.sqlQuery(
  "SELECT SUM(amount) FROM " + table + " WHERE product LIKE '%Rubber%'");

// SQL query with a registered table
// register the DataStream as view "Orders"
tableEnv.createTemporaryView("Orders", ds, $("user"), $("product"), $("amount"));
// run a SQL query on the Table and retrieve the result as a new Table
Table result2 = tableEnv.sqlQuery(
  "SELECT product, amount FROM Orders WHERE product LIKE '%Rubber%'");

// create and register a TableSink
final Schema schema = Schema.newBuilder()
    .column("product", DataTypes.STRING())
    .column("amount", DataTypes.INT())
    .build();

final TableDescriptor sinkDescriptor = TableDescriptor.forConnector("filesystem")
    .schema(schema)
    .option("path", "/path/to/file")
    .format(FormatDescriptor.forFormat("csv")
        .option("field-delimiter", ",")
        .build())
    .build();

tableEnv.createTemporaryTable("RubberOrders", sinkDescriptor);

// run an INSERT SQL on the Table and emit the result to the TableSink
tableEnv.executeSql(
  "INSERT INTO RubberOrders SELECT product, amount FROM Orders WHERE product LIKE '%Rubber%'");

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

// read a DataStream from an external source
val ds: DataStream[(Long, String, Integer)] = env.addSource(...)

// SQL query with an inlined (unregistered) table
val table = ds.toTable(tableEnv, $"user", $"product", $"amount")
val result = tableEnv.sqlQuery(
  s"SELECT SUM(amount) FROM $table WHERE product LIKE '%Rubber%'")

// SQL query with a registered table
// register the DataStream under the name "Orders"
tableEnv.createTemporaryView("Orders", ds, $"user", $"product", $"amount")
// run a SQL query on the Table and retrieve the result as a new Table
val result2 = tableEnv.sqlQuery(
  "SELECT product, amount FROM Orders WHERE product LIKE '%Rubber%'")

// create and register a TableSink
val schema = Schema.newBuilder()
  .column("product", DataTypes.STRING())
  .column("amount", DataTypes.INT())
  .build()

val sinkDescriptor = TableDescriptor.forConnector("filesystem")
  .schema(schema)
  .format(FormatDescriptor.forFormat("csv")
    .option("field-delimiter", ",")
    .build())
  .build()

tableEnv.createTemporaryTable("RubberOrders", sinkDescriptor)

// run an INSERT SQL on the Table and emit the result to the TableSink
tableEnv.executeSql(
  "INSERT INTO RubberOrders SELECT product, amount FROM Orders WHERE product LIKE '%Rubber%'")

env = StreamExecutionEnvironment.get_execution_environment()
table_env = StreamTableEnvironment.create(env)

# SQL query with an inlined (unregistered) table
# elements data type: BIGINT, STRING, BIGINT
table = table_env.from_elements(..., ['user', 'product', 'amount'])
result = table_env \
    .sql_query("SELECT SUM(amount) FROM %s WHERE product LIKE '%%Rubber%%'" % table)

# create and register a TableSink
schema = Schema.new_builder()
    .column("product", DataTypes.STRING())
    .column("amount", DataTypes.INT())
    .build()

sink_descriptor = TableDescriptor.for_connector("filesystem")
    .schema(schema)
    .format(FormatDescriptor.for_format("csv")
        .option("field-delimiter", ",")
        .build())
    .build()

t_env.create_temporary_table("RubberOrders", sink_descriptor)

# run an INSERT SQL on the Table and emit the result to the TableSink
table_env \
    .execute_sql("INSERT INTO RubberOrders SELECT product, amount FROM Orders WHERE product LIKE '%Rubber%'")

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执行查询 #

通过 TableEnvironment.executeSql() 方法可以执行 SELECT 或 VALUES 语句，并把结果收集到本地。它将SELECT语句（或VALUES语句）的结果作为 TableResult 返回。和 SELECT 语句相似，Table.execute() 方法可以执行Table对象，并把结果收集到本地客户端。 TableResult.collect() 方法返回一个可关闭的行迭代器（row iterator）。除非所有结果数据都被收集完成了，否则SELECT作业不会停止，所以应该主动使用 CloseableIterator#close() 方法关闭作业，以防止资源泄露。TableResult.print() 可以打印 SELECT 的结果到客户端的控制台中。 TableResult 上的结果数据只能被访问一次。因此 collect() 和 print() 只能二选一。

TableResult.collect() 和 TableResult.print()在不同的 checkpointing 设置下有一些差异。(流式作业开启 checkpointing，参见 checkpointing 设置)。

  • 对于没有开启 checkpoint 的批作业或流作业，TableResult.collect() 和 TableResult.print() 既不保证精确一次（exactly-once）也不保证至少一次（at-least-once）。查询结果一旦产生，客户端可以立即访问，但是，作业失败或重启将抛出异常。
  • 对于 checkpoint 设置为精确一次（exactly-once）的流式作业， TableResult.collect() 和 TableResult.print() 保证端到端的数据只传递一次。相应的checkpoint完成后，客户端才能访问结果。
  • 对于 checkpoint 设置为至少一次（at-least-once）的流式作业， TableResult.collect() 和 TableResult.print() 保证端到端的数据至少传递一次，查询结果一旦产生，客户端可以立即访问，但是可能会有同一条数据出现多次的情况。
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
StreamTableEnvironment tableEnv = StreamTableEnvironment.create(env, settings);

tableEnv.executeSql("CREATE TABLE Orders (`user` BIGINT, product STRING, amount INT) WITH (...)");

// execute SELECT statement
TableResult tableResult1 = tableEnv.executeSql("SELECT * FROM Orders");
// use try-with-resources statement to make sure the iterator will be closed automatically
try (CloseableIterator<Row> it = tableResult1.collect()) {
    while(it.hasNext()) {
        Row row = it.next();
        // handle row
    }
}

// execute Table
TableResult tableResult2 = tableEnv.sqlQuery("SELECT * FROM Orders").execute();
tableResult2.print();

val env = StreamExecutionEnvironment.getExecutionEnvironment()
val tableEnv = StreamTableEnvironment.create(env, settings)
// enable checkpointing
tableEnv.getConfig
  .set(CheckpointingOptions.CHECKPOINTING_MODE, CheckpointingMode.EXACTLY_ONCE)
tableEnv.getConfig
  .set(CheckpointingOptions.CHECKPOINTING_INTERVAL, Duration.ofSeconds(10))

tableEnv.executeSql("CREATE TABLE Orders (`user` BIGINT, product STRING, amount INT) WITH (...)")

// execute SELECT statement
val tableResult1 = tableEnv.executeSql("SELECT * FROM Orders")
val it = tableResult1.collect()
try while (it.hasNext) {
  val row = it.next
  // handle row
}
finally it.close() // close the iterator to avoid resource leak

// execute Table
val tableResult2 = tableEnv.sqlQuery("SELECT * FROM Orders").execute()
tableResult2.print()

env = StreamExecutionEnvironment.get_execution_environment()
table_env = StreamTableEnvironment.create(env, settings)
# enable checkpointing
table_env.get_config().set("execution.checkpointing.mode", "EXACTLY_ONCE")
table_env.get_config().set("execution.checkpointing.interval", "10s")

table_env.execute_sql("CREATE TABLE Orders (`user` BIGINT, product STRING, amount INT) WITH (...)")

# execute SELECT statement
table_result1 = table_env.execute_sql("SELECT * FROM Orders")
table_result1.print()

# execute Table
table_result2 = table_env.sql_query("SELECT * FROM Orders").execute()
table_result2.print()

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语法 #

Flink使用支持标准 ANSI SQL 的 Apache Calcite 解析 SQL。

下面的 BNF-grammar 描述了批处理和流处理查询中所支持 SQL 特性的超集。操作展示了支持的功能以及示例，并指示了哪些功能仅支持批处理或流处理查询。

Grammar 
query:
    values
  | WITH withItem [ , withItem ]* query
  | {
        select
      | selectWithoutFrom
      | query UNION [ ALL ] query
      | query EXCEPT query
      | query INTERSECT query
    }
    [ ORDER BY orderItem [, orderItem ]* ]
    [ LIMIT { count | ALL } ]
    [ OFFSET start { ROW | ROWS } ]
    [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY]

withItem:
    name
    [ '(' column [, column ]* ')' ]
    AS '(' query ')'

orderItem:
    expression [ ASC | DESC ]

select:
    SELECT [ ALL | DISTINCT ]
    { * | projectItem [, projectItem ]* }
    FROM tableExpression
    [ WHERE booleanExpression ]
    [ GROUP BY { groupItem [, groupItem ]* } ]
    [ HAVING booleanExpression ]
    [ WINDOW windowName AS windowSpec [, windowName AS windowSpec ]* ]

selectWithoutFrom:
    SELECT [ ALL | DISTINCT ]
    { * | projectItem [, projectItem ]* }

projectItem:
    expression [ [ AS ] columnAlias ]
  | tableAlias . *

tableExpression:
    tableReference [, tableReference ]*
  | tableExpression [ NATURAL ] [ LEFT | RIGHT | FULL ] JOIN tableExpression [ joinCondition ]

joinCondition:
    ON booleanExpression
  | USING '(' column [, column ]* ')'

tableReference:
    tablePrimary
    [ matchRecognize ]
    [ [ AS ] alias [ '(' columnAlias [, columnAlias ]* ')' ] ]

tablePrimary:
    [ TABLE ] tablePath [ dynamicTableOptions ] [systemTimePeriod] [[AS] correlationName]
  | LATERAL TABLE '(' functionName '(' expression [, expression ]* ')' ')'
  | [ LATERAL ] '(' query ')'
  | UNNEST '(' expression ')'

tablePath:
    [ [ catalogName . ] databaseName . ] tableName

systemTimePeriod:
    FOR SYSTEM_TIME AS OF dateTimeExpression

dynamicTableOptions:
    /*+ OPTIONS(key=val [, key=val]*) */

key:
    stringLiteral

val:
    stringLiteral

values:
    VALUES expression [, expression ]*

groupItem:
    expression
  | '(' ')'
  | '(' expression [, expression ]* ')'
  | CUBE '(' expression [, expression ]* ')'
  | ROLLUP '(' expression [, expression ]* ')'
  | GROUPING SETS '(' groupItem [, groupItem ]* ')'

windowRef:
    windowName
  | windowSpec

windowSpec:
    [ windowName ]
    '('
    [ ORDER BY orderItem [, orderItem ]* ]
    [ PARTITION BY expression [, expression ]* ]
    [
        RANGE numericOrIntervalExpression {PRECEDING}
      | ROWS numericExpression {PRECEDING}
    ]
    ')'

matchRecognize:
    MATCH_RECOGNIZE '('
    [ PARTITION BY expression [, expression ]* ]
    [ ORDER BY orderItem [, orderItem ]* ]
    [ MEASURES measureColumn [, measureColumn ]* ]
    [ ONE ROW PER MATCH ]
    [ AFTER MATCH
      ( SKIP TO NEXT ROW
      | SKIP PAST LAST ROW
      | SKIP TO FIRST variable
      | SKIP TO LAST variable
      | SKIP TO variable )
    ]
    PATTERN '(' pattern ')'
    [ WITHIN intervalLiteral ]
    DEFINE variable AS condition [, variable AS condition ]*
    ')'

measureColumn:
    expression AS alias

pattern:
    patternTerm [ '|' patternTerm ]*

patternTerm:
    patternFactor [ patternFactor ]*

patternFactor:
    variable [ patternQuantifier ]

patternQuantifier:
    '*'
  | '*?'
  | '+'
  | '+?'
  | '?'
  | '??'
  | '{' { [ minRepeat ], [ maxRepeat ] } '}' ['?']
  | '{' repeat '}'

Flink SQL使用的标识符词法规则(table，attribute，function names)和Java相似。

  • 大写或小写的标识符都是保留的，就算没有被引用。
  • 标识符的匹配区分大小写。
  • 和Java不同，反引号(\)允许标识符包含非字母数字（no-alphanumeric）字符(例如：“SELECT a AS `my field` FROM t”)。

字符串必须被单引号括起来（例如： SELECT 'Hello World'）。两个单引号用于转义（例如:SELECT 'It''s me'）。

Flink SQL> SELECT 'Hello World', 'It''s me';
+-------------+---------+
|      EXPR$0 |  EXPR$1 |
+-------------+---------+
| Hello World | It's me |
+-------------+---------+
1 row in set

字符串支持Unicode字符。 下面是显式使用Unicode编码的语法：

  • 使用反斜杠(\)作为转义字符 (默认)：SELECT U&'\263A'
  • 使用自定义的转义字符：SELECT U&'#263A' UESCAPE '#'

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操作 #

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