但是如果对元素进行了适当地嵌套，则有时可以模拟组合索引。
However, you can sometimes mimic a composite index if your elements are appropriately nested.
有关组合索引中的可变类型列的详细信息，请参阅“备注”部分。
For more information about variable type columns in composite indexes, see the Remarks section.
为了获取在大容量表中查询的合理的响应时间，最好为某列或者列组合定义索引。
To get reasonable response times for queries on large tables, it is a best practice to define indexes for certain columns or combination of columns.
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