从flink的官方文档，我们知道flink的编程模型分为四层，sql层是最高层的api，Table api是中间层，DataStream/DataSet Api 是核心，stateful Streaming process层是底层实现。

其中，

flink dataset api使用及原理介绍了DataSet Api

flink DataStream API使用及原理介绍了DataStream Api

flink中的时间戳如何使用？---Watermark使用及原理介绍了底层实现的基础Watermark

flink window实例分析介绍了window的概念及使用原理

Flink中的状态与容错介绍了State的概念及checkpoint，savepoint的容错机制

上上篇<使用flink Table &Sql api来构建批量和流式应用(1)Table的基本概念>介绍了Table的基本概念及使用方法

上篇<使用flink Table &Sql api来构建批量和流式应用(2)Table API概述>

本篇主要看看Flink Sql 有哪些功能及背后的原理

1. sql功能

 体现在org.apache.flink.table.api.TableEnvironment，目前flink仅支持select和insert操作

(1) select 

/** * Evaluates a SQL query on registered tables and retrieves the result as a {@link Table}.

*

* <p>All tables referenced by the query must be registered in the TableEnvironment.

* A {@link Table} is automatically registered when its {@link Table#toString()} method is

* called, for example when it is embedded into a String.

* Hence, SQL queries can directly reference a {@link Table} as follows:

*

* <pre>

* {@code * Table table = ...;

* String tableName = table.toString();

* // the table is not registered to the table environment

* tEnv.sqlQuery("SELECT * FROM tableName");

* }

* </pre>

*

* @param query The SQL query to evaluate.

* @return The result of the query as Table

*/ Table sqlQuery(String query);

(2) update（当前仅支持insert）

/** * Evaluates a SQL statement such as INSERT, UPDATE or DELETE; or a DDL statement;

* NOTE: Currently only SQL INSERT statements are supported.

*

* <p>All tables referenced by the query must be registered in the TableEnvironment.

* A {@link Table} is automatically registered when its {@link Table#toString()} method is

* called, for example when it is embedded into a String.

* Hence, SQL queries can directly reference a {@link Table} as follows:

*

* <pre>

* {@code * // register the configured table sink into which the result is inserted.

* tEnv.registerTableSink("sinkTable", configuredSink);

* Table sourceTable = ...

* String tableName = sourceTable.toString();

* // sourceTable is not registered to the table environment

* tEnv.sqlUpdate(s"INSERT INTO sinkTable SELECT * FROM tableName");

* }

* </pre>

*

* @param stmt The SQL statement to evaluate.

*/void sqlUpdate(String stmt);

/** * Evaluates a SQL statement such as INSERT, UPDATE or DELETE; or a DDL statement;

* NOTE: Currently only SQL INSERT statements are supported.

*

* <p>All tables referenced by the query must be registered in the TableEnvironment.

* A {@link Table} is automatically registered when its {@link Table#toString()} method is

* called, for example when it is embedded into a String.

* Hence, SQL queries can directly reference a {@link Table} as follows:

*

* <pre>

* {@code * // register the configured table sink into which the result is inserted.

* tEnv.registerTableSink("sinkTable", configuredSink);

* Table sourceTable = ...

* String tableName = sourceTable.toString();

* // sourceTable is not registered to the table environment

* tEnv.sqlUpdate(s"INSERT INTO sinkTable SELECT * FROM tableName", config);

* }

* </pre>

*

* @param stmt The SQL statement to evaluate.

* @param config The {@link QueryConfig} to use.

*/voidsqlUpdate(String stmt, QueryConfig config);