GET DESCRIPTOR descriptor_name :cvariable = descriptor_header_item [, ... ]
GET DESCRIPTOR descriptor_name VALUE column_number :cvariable = descriptor_item [, ... ]

描述

GET DESCRIPTOR 从 SQL 描述符区域检索有关查询结果集的信息，并将其存储到主机变量中。在使用此命令将信息传输到主机语言变量之前，通常使用 FETCH 或 SELECT 填充描述符区域。

此命令有两种形式：第一种形式检索描述符 “header” 项，这些项适用于整个结果集。行计数就是一个示例。第二种形式需要列号作为附加参数，检索有关特定列的信息。列名和实际列值就是示例。

参数

示例

检索结果集中列数量的示例

EXEC SQL GET DESCRIPTOR d :d_count = COUNT;

检索第一列中数据长度的示例

EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;

检索第二列的数据正文作为字符串的示例

EXEC SQL GET DESCRIPTOR d VALUE 2 :d_data = DATA;

以下是执行 SELECT current_database(); 的完整过程的示例，并显示列数、列数据长度和列数据

int
main(void)
{
EXEC SQL BEGIN DECLARE SECTION;
    int  d_count;
    char d_data[1024];
    int  d_returned_octet_length;
EXEC SQL END DECLARE SECTION;

    EXEC SQL CONNECT TO testdb AS con1 USER testuser;
    EXEC SQL SELECT pg_catalog.set_config('search_path', '', false); EXEC SQL COMMIT;
    EXEC SQL ALLOCATE DESCRIPTOR d;

    /* Declare, open a cursor, and assign a descriptor to the cursor  */
    EXEC SQL DECLARE cur CURSOR FOR SELECT current_database();
    EXEC SQL OPEN cur;
    EXEC SQL FETCH NEXT FROM cur INTO SQL DESCRIPTOR d;

    /* Get a number of total columns */
    EXEC SQL GET DESCRIPTOR d :d_count = COUNT;
    printf("d_count                 = %d\n", d_count);

    /* Get length of a returned column */
    EXEC SQL GET DESCRIPTOR d VALUE 1 :d_returned_octet_length = RETURNED_OCTET_LENGTH;
    printf("d_returned_octet_length = %d\n", d_returned_octet_length);

    /* Fetch the returned column as a string */
    EXEC SQL GET DESCRIPTOR d VALUE 1 :d_data = DATA;
    printf("d_data                  = %s\n", d_data);

    /* Closing */
    EXEC SQL CLOSE cur;
    EXEC SQL COMMIT;

    EXEC SQL DEALLOCATE DESCRIPTOR d;
    EXEC SQL DISCONNECT ALL;

    return 0;
}

执行示例后，结果将如下所示

d_count                 = 1
d_returned_octet_length = 6
d_data                  = testdb

兼容性

GET DESCRIPTOR 在 SQL 标准中指定。

另请参见

ALLOCATE DESCRIPTOR，SET DESCRIPTOR