• Indexes improve query performance by avoiding a full table scan.

    索引能够避免扫描,从而能够提高查询性能

    youdao

  • The preceding query requires MySQL to perform a full table scan, the slowest type of query for a large table.

    上面的那个查询执行扫描对于一个表来说是最慢的一查询方式。

    youdao

  • The predicates in the query in Listing 7 are weakly selective so that a full table scan of the PDBXML table is required.

    清单7查询谓词选择性弱,因此需要pdbxml进行扫描

    youdao

  • Most often, you want only a small subset of the data in the table, so a full table scan wastes a lot of disk I/O and therefore time.

    通常来说,可能希望获得数据一个子集因此扫描浪费大量磁盘I/O因此也就会浪费大量时间。

    youdao

  • If there is no index on ucname, the DBMS still does a full table scan, but it need not do any further processing on the data to determine whether or not it satisfies the query.

    如果没有为ucname创建索引DBMS仍然执行扫描但是不会数据进行进一步处理判断是否满足查询

    youdao

  • If you assume that there is an index on COL1 in the above example, if COL1 is type-cast instead of the RHS, then the index will be bypassed and the query will perform a full table scan.

    假设上面示例中的COL1索引如果对COL1而不是RHS执行类型转换,那么绕过索引,查询会执行扫描

    youdao

  • If you assume that there is an index on COL1 in the above example, if COL1 is type-cast instead of the RHS, then the index will be bypassed and the query will perform a full table scan.

    假设上面示例中的COL1索引如果对COL1而不是RHS执行类型转换,那么绕过索引,查询会执行扫描

    youdao

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