postgresql – 如何从执行的预准备语句中获取$1参数的值(使用cur

发布时间：2020-12-13 18:10:56 所属栏目：百科来源：网络整理

导读：在触发器中我想看看sql查询触发了这个触发器.我使用了 postgresql(8.4)的current_query()函数. 一切都很好,但是如果触发器是通过预备语句执行的,我会获得占位符($1)而不是正确的值.例如(已记录的查询)： delete from some_table where id=$1 有没有办法获得/

在触发器中我想看看sql查询触发了这个触发器.我使用了 postgresql(8.4)的current_query()函数.

一切都很好,但是如果触发器是通过预备语句执行的,我会获得占位符($1)而不是正确的值.例如(已记录的查询)：

delete from some_table where id=$1

有没有办法获得/拥有这个值/参数？

已编辑(已添加示例)：

--table for saving query
create table log_table (
query text
)

--table for trigger
create table some_table (
id text
)
--function itself
CREATE FUNCTION save_query() RETURNS trigger AS $$
    switch $TG_op {
    DELETE {
            spi_exec "INSERT INTO log_table (query) VALUES (current_query())"
        }
    default {
            return OK
        }
    }
    return OK
$$LANGUAGE pltcl;

创建一个触发器：

create trigger test_trigger before delete on some_table for each row execute procedure save_query();

准备好的语句是从hibernate执行的.

再次编辑(添加了java部分)

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

public class DeleteUsingPreparedStmt {

    public static void main(String[] args) {
        try {
            String deleteString = "delete from floors where id = ? ";
            final int idToDelte = 1;

            Class.forName("org.postgresql.Driver");
            String url = "jdbc:postgresql://127.0.0.1:5432/YOUR_DATABASE";
            Connection conn = DriverManager.getConnection(url,"user","password");

            PreparedStatement deleteStmt = conn.prepareStatement(deleteString);
            deleteStmt.setInt(1,idToDelte);
            deleteStmt.executeUpdate();
        } catch (Exception e) {
            //hide me :)
        }
    }
}

你需要一个jdbc驱动程序 – click.

这是一些工作代码(对于Debian用户：只需安装postgresql-pltcl-8.4包并运行CREATE LANGUAGE pltcl;)

CREATE TABLE log_table (
    id serial,query text
);

CREATE TABLE floors (
    id serial,value text
);

INSERT INTO floors(value) VALUES ('aaa'),('bbb');

CREATE OR REPLACE FUNCTION save_query() RETURNS trigger AS $$
    switch $TG_op {
        DELETE {
            spi_exec "INSERT INTO log_table (query) VALUES (current_query())"
        }
        default {
            return OK
        }
    }
    return OK
$$LANGUAGE pltcl;

CREATE TRIGGER test_trigger
    BEFORE DELETE ON floors
    FOR EACH ROW
    EXECUTE PROCEDURE save_query();

但是我无法在预准备语句中获取占位符(它返回EXECUTE deleteFromFloors(2);)：

TABLE log_table;
 id | query 
----+-------
(0 rows)
DELETE FROM floors WHERE id = 1;
DELETE 1
TABLE log_table;
 id |              query               
----+----------------------------------
  1 | DELETE FROM floors WHERE id = 1;
(1 row)
PREPARE deleteFromFloors(integer) AS
    DELETE FROM floors WHERE id = $1;
PREPARE
EXECUTE deleteFromFloors(2);
DELETE 1
TABLE log_table;
 id |              query               
----+----------------------------------
  1 | DELETE FROM floors WHERE id = 1;
  2 | EXECUTE deleteFromFloors(2);
(2 rows)

编辑：

作为一种解决方法使用OLD记录(在Tcl中表示为数组),从那里获取id列并使用replace函数来代替$1.这里有两个解决方案：PL / pgSQL和PL / Tcl：

CREATE OR REPLACE FUNCTION save_query() RETURNS TRIGGER AS $$
BEGIN
    INSERT INTO log_table (query)
        VALUES (replace(current_query(),'$1',OLD.id::text));
    RETURN OLD;
END;
$$LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION save_query() RETURNS trigger AS $$
    switch $TG_op {
        DELETE {
            spi_exec "INSERT INTO log_table (query)
                VALUES (replace(current_query(),'$1','$OLD(id)'))"
        }
        default {
            return OK
        }
    }
    return OK
$$LANGUAGE pltcl;

结果：

java -classpath '.:postgresql-8.4-702.jdbc4.jar' DeleteUsingPreparedStmt

TABLE log_table;
 id |              query              
----+---------------------------------
  1 | delete from floors where id = 1

(1排)

（编辑：李大同）

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