INSERT…返回和pl/pgsql返回之间有什么区别？_Sql_Postgresql_Sql Insert

INSERT…返回和pl/pgsql返回之间有什么区别？

sql postgresql

INSERT…返回和pl/pgsql返回之间有什么区别？,sql,postgresql,sql-insert,Sql,Postgresql,Sql Insert,（交叉过账至） INSERT INTO foo VALUES (2); CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS $$BEGIN

（交叉过账至）

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

假设如下：观察这种行为我可以在我的视图中插入：

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

它起作用了；没问题。现在，如果我将触发函数更改为
第二条语句返回的不是两条语句，而是一条语句

插入带有返回
子句的

，如下所示：

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

然后，插入会导致错误：

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

文件 :

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

带有表达式的RETURN终止函数并返回表达式对调用方的值

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

可选的RETURNING子句导致INSERT计算并返回基于实际插入的每行的值

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

（我的重点）

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

我的问题有两个：

真正意义上的区别是什么在这两个关键字之间，以一种允许我预测错误吗

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

错误的含义是什么，即自触发以来函数需要返回一个值，因为插入是触发器函数的最终语句，为什么查询没有结果数据的目的地

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

也请阅读此摘录（来自同一链接：）

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

如果INSERT命令包含RETURNING子句，则结果将为类似于包含列和的SELECT语句返回列表中定义的值，在行上计算由命令插入

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement

是的，我知道这个描述可能会让人困惑：）
简单地说：returning子句的工作原理类似于SELECT，它从表中检索行，将它们组合成一个结果集，并将该结果集直接发送到客户端（client=gui工具、java/c++程序等）。客户端必须知道如何使用某种API读取此结果集（打开它，从中检索行、值等）-例如，在java中，有用于处理结果集-->查找

resultset

类的JDBC API。

所以，returning子句创建一个resultset并将其发送到客户机，方法与普通SELECT相同。

函数中的Return语句终止该函数，并将表达式的值返回给调用方。
不是直接发送给客户机，而是发送给调用者-发送给调用此函数的其他函数/过程或SELECT语句。并且不返回结果集（一组行），而是返回值

INSERT INTO foo VALUES (2);

CREATE OR REPLACE FUNCTION insert_foo() RETURNS TRIGGER AS                                                     
$$BEGIN                                                                                                        
  INSERT INTO base_foo VALUES (NEW.size)                                                                       
  RETURNING NEW;                                                                                               
END$$ language plpgsql;

INSERT INTO foo VALUES (3);                                                                                    
ERROR:  query has no destination for result data                                                               
CONTEXT:  PL/pgSQL function insert_foo() line 2 at SQL statement