描述集合变量

当使用 USING SQL DESCRIPTOR 或 INTO 子句时，DESCRIBE 语句提供有关集合变量的信息。在打开 Select 或 Insert 游标之后，必须发出 DESCRIBE 语句，因为 OPEN...USING 语句指定了要使用的集合变量的名称。

下一个 GBase 8s ESQL/C 代码段动态地选择 :a_set 集合变量的元素进入称为 desc1 的系统描述符区域：

EXEC SQL BEGIN DECLARE SECTION;
      client collection a_set;
      int i, set_count;
      int element_type, element_value;
EXEC SQL END DECLARE SECTION;

EXEC SQL allocate collection :a_set;
EXEC SQL allocate descriptor 'desc1';
EXEC SQL select set_col into :a_set from table1;
EXEC SQL prepare set_id from 'select * from table(?)'

EXEC SQL declare set_curs cursor for set_id;
EXEC SQL open set_curs using :a_set;
EXEC SQL describe set_id using sql descriptor 'desc1';

do
{
      EXEC SQL fetch set_curs using sql descriptor 'desc1';
      ...
      EXEC SQL get descriptor 'desc1' :set_count = count;
      for (i = 1; i <= set_count; i++)
      {
         EXEC SQL get descriptor 'desc1' value :i
            :element_type = TYPE;
         switch
         {
            case SQLINTEGER:
               EXEC SQL get descriptor 'desc1' value :i
                  :element_value = data;
            ...
         } /* end switch */
      } /* end for */
} while (SQLCODE == 0);

EXEC SQL close set_curs;
EXEC SQL free set_curs;
EXEC SQL free set_id;
EXEC SQL deallocate collection :a_set;
EXEC SQL deallocate descriptor 'desc1';