我正在尝试从 PostgreSQL 中检索记录
我使用以下脚本创建数据库、表并用一些记录填充它：
psql << "EOF"
CREATE DATABASE todo;
\c todo
CREATE TABLE items
(
id serial PRIMARY KEY,
task VARCHAR(40) NOT NULL,
complete boolean
);
INSERT INTO items (id, task, complete) VALUES (1, 'task1', true);
INSERT INTO items (id, task, complete) VALUES (2, 'task2', true);
INSERT INTO items (id, task, complete) VALUES (3, 'task3', true);
INSERT INTO items (id, task, complete) VALUES (4, 'task4', true);
INSERT INTO items (id, task, complete) VALUES (5, 'task5', false);
INSERT INTO items (id, task, complete) VALUES (6, 'task6', false);
EOF
我使用 a) 结构和 b) 单个变量来处理问题。方法 a) 无法完整解析布尔字段。这是程序：
#include <stdio.h>
#include <stdlib.h>
#include <ecpglib.h>
int
main(void)
{
#if ENABLE_DEBUG
ECPGdebug(1, stderr);
#endif
EXEC SQL WHENEVER SQLERROR sqlprint;
EXEC SQL BEGIN DECLARE SECTION;
/* Use structure as host variable */
typedef struct {
int id;
char task[40];
bool complete;
} item_t;
item_t item;
/* Use individual variables as host variables */
int id;
char task[40];
bool complete;
EXEC SQL END DECLARE SECTION;
memset(&item, 0, sizeof(item_t));
EXEC SQL CONNECT TO todo;
/*
* Use structure as host variable
*/
EXEC SQL DECLARE cur1 CURSOR FOR
SELECT id, task, complete
FROM items;
EXEC SQL OPEN cur1;
printf("sizeof(item_t) = %ld\n", sizeof(item));
printf(" sizeof(item.int) = %ld\n", sizeof(item.id));
printf(" sizeof(item.task) = %ld\n", sizeof(item.task));
printf(" sizeof(item.complete) = %ld\n", sizeof(item.complete));
printf("\n"
"Using structure variable\n"
"------------------------\n");
EXEC SQL WHENEVER NOT FOUND DO BREAK;
while (1)
{
EXEC SQL FETCH FROM cur1 INTO :item;
printf("id=%d, task=%s, complete=%d\n\n",
item.id, item.task, item.complete);
}
EXEC SQL CLOSE cur1;
/*
* Use individual variables as host variables
*/
EXEC SQL DECLARE cur2 CURSOR FOR
SELECT id, task, complete
FROM items;
EXEC SQL OPEN cur2;
printf("sizeof(int) = %ld\n", sizeof(id));
printf("sizeof(task) = %ld\n", sizeof(task));
printf("sizeof(complete) = %ld\n", sizeof(complete));
printf("\n"
"Using individual variables\n"
"--------------------------\n");
EXEC SQL WHENEVER NOT FOUND DO BREAK;
while (1)
{
EXEC SQL FETCH FROM cur2 INTO :id, :task, :complete;
printf("id=%d, task=%s, complete=%d\n",
id, task, complete);
}
EXEC SQL CLOSE cur2;
EXEC SQL DISCONNECT ALL;
return 0;
}
输出：
sizeof(item_t) = 48
sizeof(item.int) = 4
sizeof(item.task) = 40
sizeof(item.complete) = 1
Using structure variable
------------------------
SQL error: could not convert boolean value: size mismatch, on line 80
id=1, task=task1, complete=0
SQL error: could not convert boolean value: size mismatch, on line 80
id=2, task=task2, complete=0
SQL error: could not convert boolean value: size mismatch, on line 80
id=3, task=task3, complete=0
SQL error: could not convert boolean value: size mismatch, on line 80
id=4, task=task4, complete=0
SQL error: could not convert boolean value: size mismatch, on line 80
id=5, task=task5, complete=0
SQL error: could not convert boolean value: size mismatch, on line 80
id=6, task=task6, complete=0
sizeof(int) = 4
sizeof(task) = 40
sizeof(complete) = 1
Using individual variables
--------------------------
id=1, task=task1, complete=1
id=2, task=task2, complete=1
id=3, task=task3, complete=1
id=4, task=task4, complete=1
id=5, task=task5, complete=0
id=6, task=task6, complete=0