Java Web Lightweight Development Interview Tutorial reading notes: The factors we need to weigh when building an index

Scene one, the size of the data table is small, thousands of rows, even if the index is not built, the return time of the query statement is not long, then the significance of the index is not big. Of course, if the thousands of rows, the index occupies less space, so in this case, at most, belong to the "cost-effective" is not high.

Scene two, a product table has millions of items of information, at the same time every day at a point, to update about 100,000 of the product information, and now use the WHERE statement to query a particular product (such as WHERE name = ' XXX ') is very slow. Indexing can be built to improve query efficiency, but it is time-consuming to rebuild the index every day when data is updated.

This requires a comprehensive consideration, and even the ability to delete the index before updating, and then rebuilding it.

Scenario three, as can be seen in Figure 2.1, because the data table ID values are not the same, so the index can play a relatively large role. Conversely, if a field has a high repetition rate, such as a gender field, or if most of the value of a field is empty (null), it is not recommended to Jianjian the word index.

Please remember that there must be a business need to build the index. For example, in a commodity table, we often have to query according to name, if there is no index, query speed is very slow, then we need to build an index. However, in project development, it is not necessary to index a number if it is not often queried according to the product number.

Finally, the index is to pay a price, nothing to build, at the same time on a table also can not build too many indexes.

Read the Java Web Lightweight Development Interview tutorial for more information

https://baike.baidu.com/item/Java%20Web%E8%BD%BB%E9%87%8F%E7%BA%A7%E5%BC%80%E5%8F%91%E9%9D%A2%E8%AF%95%E6%95% 99%e7%a8%8b/22038502?fr=aladdin

Java Web Lightweight Development Interview Tutorial reading notes: The factors we need to weigh when building an index