Kadb中的ecpg编程
测试程序：
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
// 相当于高级程序语言的全局变量定义
EXEC SQL BEGIN DECLARE SECTION; // 主变量声明开始
const char* target1 = "postgres@192.168.85.155:5432"; // 数据库1
const char* user1 = "postgres";
const char* passwd1 = "123456";
const char* target2 = "test@192.168.85.155:5432"; // 数据库2
const char* user2 = "postgres";
const char* passwd2 = "123456";
int rows = 0; // 表行数
char sno[10]; // s表的四个属性（s表是自定义的）
char sname[20];
int status;
char city[20];
EXEC SQL END DECLARE SECTION; // 主变量声明结束
int main() {
EXEC SQL WHENEVER SQLERROR SQLPRINT; // error 时输出错误信息
// 连接至数据库1
EXEC SQL CONNECT TO :target1 USER :user1 USING :passwd1;
printf("\n已连接%s\n", target1);
EXEC SQL SET AUTOCOMMIT TO ON;
EXEC SQL drop database if exists test; // 删除 spj 数据库
EXEC SQL create database test; // 创建 spj 数据库
// 断开数据库1
EXEC SQL DISCONNECT CURRENT; // 这个不写也能运行，不知道有没有风险
printf("\n已断开%s\n", target1);
// 连接至数据库2
EXEC SQL CONNECT TO :target2 USER :user2 USING :passwd2;
printf("\n已连接%s\n", target2);
// 下面五条exec sql，建表及插入
EXEC SQL drop table if exists s;
EXEC SQL CREATE TABLE IF NOT EXISTS s(sno char(10) primary key, sname char(20) unique, status int, city char(20));
EXEC SQL insert into s(sno, sname, status, city) values('s1', 'APEX LEGEND', 114514, 'Wuhan');
EXEC SQL insert into s(sno, sname, status, city) values('s2', 'DEVIL MAY CRY5', 616161, 'Wuhan');
EXEC SQL insert into s(sno, sname, status, city) values('s3', 'WARFRAME', 123456, 'Wuhan');
// 写入中文，数据库内是utf8，控制台输出的是gbk，会乱码
EXEC SQL END; // 结束事务块
EXEC SQL BEGIN; // BEGIN 事务块，DECLARE只能在事务块中使用
// 定义游标，相当于每次读表的一行
EXEC SQL DECLARE iterator CURSOR FOR
select sno, sname, status, city
from s;
EXEC SQL OPEN iterator; // 打开游标
EXEC SQL select count(*) into :rows from s; // 获取行数，只有主变量能被sql赋值
int flag = 0;
while (rows --) {
EXEC SQL fetch iterator into :sno, :sname, :status, :city; // fetch 获取一行元组
if (flag ++ == 0) { // 第一次把列名输出
printf("\n%-10s %-20s %-10s %-20s \n", "sno", "sname", "status", "city");
}
printf("%-10s %-20s %-10d %-20s \n", sno, sname, status, city);
}
EXEC SQL CLOSE iterator; // 关闭游标
EXEC SQL END; // 结束事务块
EXEC SQL DISCONNECT CURRENT; // 断开数据库2
printf("\n已断开%s\n", target2);
return 0;
}
编译：
/usr/local/pgsql/bin/ecpg proc.pgc
cc -I/usr/local/pgsql/include -c proc.c
cc -o proc proc.o -L/usr/local/pgsql/lib --lecpg
运行：
-bash-4.2$ ./proc
已连接postgres@192.168.85.155:5432
已断开postgres@192.168.85.155:5432
已连接test@192.168.85.155:5432
SQL error: there is already a transaction in progress
sno sname status city
s1 APEX LEGEND 114514 Wuhan s1
s2 DEVIL MAY CRY5 616161 Wuhan s2
s3 WARFRAME 123456 Wuhan s3
已断开test@192.168.85.155:5432