在 postgres 中插入之前截断表

Question

我正在尝试创建一种机制，每次调用插入命令时都会截断表。

首先我尝试创建一个函数，该函数获取行数组并在插入之前截断表格：

CREATE OR REPLACE FUNCTION insert_customers(customers customer[])
    RETURNS VOID AS 
$$  
BEGIN
    TRUNCATE TABLE Customers;
    INSERT INTO Customers (CustomerID, CustomerName) SELECT * FROM UNNEST(customers::Customer[]);
END
$$
LANGUAGE plpgsql;

其中 Customer 是用户定义的类型，表示 Customers 表中的一行：

CREATE TYPE Customer AS (
  customerid VARCHAR(100),
  customername VARCHAR(100));

当我从 psql 调用函数时，它起作用了：

SELECT * FROM insert_customers(ARRAY[ROW('ID1', 'Name1'),ROW('ID2', 'Name2')]::Customer[]);

但我还没有找到从我的 java 代码中执行此插入的方法：

String[][] customers = new String[2][];
customers[0] = new String[] { "ID1", "Name1" };
customers[1] = new String[] { "ID2", "Name2" };    

Array sqlArray = connection.createArrayOf("customer", customers);    

CallableStatement cstmt = connection.prepareCall("{ call insert_customers(?) }");
cstmt.setArray(1, sqlArray);
cstmt.execute();

创建了以下语句：

select * from insert_customers ('{{"ID1", "Name1"},{"ID2", "Name2"}}') as result

并抛出以下异常：

org.postgresql.util.PSQLException: ERROR: malformed record literal: "ID1"\n Detail: Missing left parenthesis.

然后我尝试创建一个触发器，该触发器将在插入事件时截断表：

CREATE TRIGGER on_insert_customers
    BEFORE INSERT ON Customers
    EXECUTE PROCEDURE truncate_customers();

truncate_customers 是：

CREATE OR REPLACE FUNCTION truncate_customers()
    RETURNS TRIGGER AS 
$$  
BEGIN
    TRUNCATE TABLE Customers;   
END
$$
LANGUAGE plpgsql;

这引发了异常：

cannot TRUNCATE "customers" because it is being used by active queries in this session

有什么想法？？？

Answer 1

修改函数

查询一个文本数组的非嵌套元素对：

select cols[1], cols[2]
from (
    select (ordinality- 1)/2, array_agg(unnest) cols
    from unnest('{"id1", "name1", "id2", "name2"}'::text[]) with ordinality
    group by 1
    ) s

 cols | cols  
------+-------
 id1  | name1
 id2  | name2
(2 rows)

在你的函数中使用它，这样它就可以有一个文本数组作为参数：

create or replace function insert_customers(text[])
returns void language plpgsql as $$  
begin
    truncate table customers;
    insert into customers (customerid, customername)
    select cols[1], cols[2]
    from (
        select (ordinality- 1)/2, array_agg(unnest) cols
        from unnest($1) with ordinality
        group by 1
        ) s;
end $$;

select insert_customers('{"id1", "name1", "id2", "name2"}');

修改触发函数

您不能在触发器中截断表，但可以删除所有行：

...
    delete from Customers;
    return new;
...