问答问题：在 INDEX 查询中，为什么 SELECT 查询比 SQL 中的其他 UPDATE 或 INSERT 查询快得多？

Question

In INDEX Query, why the SELECT query is much faster than other UPDATE or INSERT query in SQL?

Answer 1

In simplest, select is pulling data already written. Update and insert have to write the data to the pages and also update indexes, so it needs to traverse all possible indexes of impacted tables.

Additionally, (credit to obe), select queries can take advantage of the cache if the data is associated with a prior query. It does not need to go back to the original data pages / indexes to re-pull the data.