PostgreSQL特性矩阵解析系列22之SQLDA support for ECPG

我们可以使用下列语句连接到一个数据库：
EXEC SQL CONNECT TO target [AS connection-name] [USER user-name];

target可以用下列方法指定：

dbname[@hostname][:port]
tcp:postgresql://hostname[:port][/dbname][?options]
unix:postgresql://hostname[:port][/dbname][?options]
一个包含上述形式之一的 SQL 字符串
到一个包含上述形式之一（参见例子）的字符变量的引用
DEFAULT

EXEC SQL CONNECT TO mydb@sql.mydomain.com;

EXEC SQL CONNECT TO unix:postgresql://sql.mydomain.com/mydb AS myconnection USER john;

EXEC SQL BEGIN DECLARE SECTION;
const char *target = "mydb@sql.mydomain.com";
const char *user = "john";
const char *passwd = "secret";
EXEC SQL END DECLARE SECTION;
 ...
EXEC SQL CONNECT TO :target USER :user USING :passwd;
/* 或者 EXEC SQL CONNECT TO :target USER :user/:passwd; */

建表语句测试表
create database test;
create test (id int);

test.pgc   #扩展名.pgc

##内容##
#include <stdio.h>
#include <stdlib.h>

int main ( void )
{
EXEC SQL BEGIN DECLARE SECTION;
char *target="test@127.0.0.1:5432";
char *user="postgres";
char *passwd="123456";

int pid;

EXEC SQL END DECLARE SECTION;

        exec sql connect to :target user :user using :passwd;

        if (sqlca.sqlcode == 0 )
                printf("connect sucesess ... \n");
        else {
                printf("connect faild ... ... \n");
        exit(0);
        }
    
    printf("add ... \n");
    exec sql begin;
    exec sql insert into test(id) values(1);
    exec sql commit;
    printf("query ... \n");
    
    exec sql select id into :pid from test;
    printf(" pid = %d \n",pid);
}

Makefile文件内容

TARGET = test  #pgc文件名
CC = gcc
CFLAGS = -g -O2 -c -fPIC -DDEBUG
ECPG = ecpg -c
AR = ar -rcvl
RANLIB = ranlib
INCLDIR = -I. -I/opt/pgsql124/include/ # 改成当前环境实际路径 libecpg.so.6
LIBDIR = -L. -L$(HOME)/lib -L/opt/pgsql124/lib/ # 改成当前环境实际路径 libpgtypes.so.3
LIBS = -lecpg
OBJ =
all:$(TARGET)
clean:
  rm -f $(TARGET) *.o core.* .*.swp
test:test.o #pgc文件名
  $(CC) -o $@ $^ $(LIBDIR) $(LIBS)
# ################################################################################
.SUFFIXES:
.SUFFIXES:.c .o .pgc
.pgc.c:
  $(ECPG) $(INCLUDE) $<
.c.o:
  $(CC) $(CFLAGS) $(INCLDIR) $<