Shulou(Shulou.com)05/31 Report--

This article mainly introduces "how to optimize SQL code". In daily operation, I believe many people have doubts about how to optimize SQL code. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts of "how to optimize SQL code". Next, please follow the editor to study!

The way most people write it at present

When the REVIEW code is repeated, it is found that the business code needs to query whether there are records according to one or more conditions, regardless of how many records there are. The common SQL and code writing methods are as follows

# SQL: SELECT count (*) FROM table WHERE a = 1 AND b = 2 # Java: int nums = xxDao.countXxxxByXxx (params); if (nums > 0) {/ / when it exists, execute the code here} else {/ / execute the code here} if it does not exist

Does it feel very OK? there is no problem.

Optimization scheme

It is recommended to write as follows:

# SQL: SELECT 1 FROM table WHERE a = 1 AND b = 2 LIMIT 1 # Java: Integer exist = xxDao.existXxxxByXxx (params); if (exist! = NULL) {/ / when it exists, execute the code here} else {/ / when it doesn't exist, execute the code here}

SQL no longer uses count, but uses LIMIT 1 instead, so that when you encounter an entry in a database query, you can return it instead of looking up how many items there are left. You can directly determine whether it is empty in the business code.

At this point, the study on "how to optimize SQL code" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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