# 使用游标
使用游标可以检索出多行的结果集，应用程序必须声明一个游标并且从游标中抓取每一行数据。
1. 声明一个游标： 
   ```
   EXEC SQL DECLARE c CURSOR FOR select * from tb1;
   ```
   
   
2. 打开游标： 
   ```
   EXEC SQL OPEN c;
   ```
   
   
3. 从游标中抓取一行数据： 
   ```
   EXEC SQL FETCH 1 in c into :a, :str;
   ```
   
   
4. 关闭游标： 
   ```
   EXEC SQL CLOSE c;
   ```
   
   
更多游标的使用细节请参见[DECLARE](https://support.huaweicloud.com/distributed-devg-v3-gaussdb/gaussdb-12-0186.html#ZH-CN_TOPIC_0000002235389789)，关于FETCH命令的细节请参见[FETCH](https://support.huaweicloud.com/distributed-devg-v3-gaussdb/gaussdb-12-0603.html#ZH-CN_TOPIC_0000002200190374)。
完整使用示例：
```
#include <string.h>
#include <stdlib.h>
int main(void)
{
exec sql begin declare section;
    int *a = NULL;
    char *str = NULL;
exec sql end declare section;
    int count = 0;
    exec sql connect to postgres ;
    exec sql set autocommit to off;
    exec sql begin;
    exec sql drop table if exists tb1;
    exec sql create table tb1(id int, info text);
    exec sql insert into tb1 (id, info) select generate_series(1, 100000), 'test';
    exec sql select count(*) into :a from tb1;
    printf ("a is %d\n", *a);
    exec sql commit;
    // 定义游标
    exec sql declare c cursor for select * from tb1;
    // 打开游标
    exec sql open c;
    exec sql whenever not found do break;
    while(1) {
        // 抓取数据
        exec sql fetch 1 in c into :a, :str;
        count++;
        if (count == 100000) {
            printf("Fetch res: a is %d, str is %s", *a, str);
        }
    }
    // 关闭游标
    exec sql close c;
    exec sql set autocommit to on;
    exec sql drop table tb1;
    exec sql disconnect;
    ECPGfree_auto_mem();
    return 0;
}
```