达梦 联合索引规则 排序
    英文回答：
    Compound Index Rules in Dameng.
    Compound indexes are created using multiple columns in a table. The order of the columns in the index is important, as it determines the sort order of the data. The following rules apply to the order of columns in a compound index:
    The first column in the index is the most significant column. It is used to sort the data in ascending order.
sort of in order    The second column in the index is the next most significant column. It is used to sort the data in ascending order within each group of data that has the same value in the first column.
    The third column in the index is the next most significant column, and so on.
    For example, the following index is created on the `customers` table:
    CREATE INDEX idx_customers ON customers (last_name, first_name);
    This index will sort the data in the `customers` table in ascending order by last name, and then in ascending order by first name within each last name group.
    The order of the columns in a compound index can be used to improve the performance of queries that use the index. For example, if you frequently query the `customers` table to find all customers with a particular last name, then the `idx_customers` index can be used to speed up the query.
    中文回答：
    达梦联合索引规则 排序。
    联合索引是使用表中的多列创建的。索引中列的顺序很重要，因为它决定了数据的排序顺序。联合索引中列的顺序遵循以下规则：
    索引中的第一列是最重要的列。它用于按升序对数据进行排序。
    索引中的第二列是次重要的列。它用于对具有第一列相同值的每组数据按升序对数据进行排序。
    索引中的第三列是次重要的列，依此类推。
    例如，在 `customers` 表上创建以下索引：
    CREATE INDEX idx_customers ON customers (last_name, first_name);
    此索引将按姓氏升序对 `customers` 表中的数据进行排序，然后在每个姓氏组内按名字升序对数据进行排序。
    联合索引中列的顺序可用于提高使用索引的查询的性能。例如，如果您经常查询 `customers` 表以查具有特定姓氏的所有客户，则可以使用 `idx_customers` 索引来加快查询速度。

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