Shulou(Shulou.com)06/02 Report--

This article will explain in detail what the SQL writing specifications are, and the content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

Absolutely forbid 1: multiple tables with a long list of left join associations

Absolutely forbid 2: the act of not writing comments

Absolutely forbid 3: table aliases use a single meaningless letter

4: nested queries with more than two layers are absolutely prohibited

Recommendation 1: when making a fuzzy query, the string in the prohibition condition begins with "%" directly.

Recommendation 2: when merging result sets (union or union all), if there is no need for result deduplication, union all must be used, but union; cannot be used and data set deduplication must be minimized

Suggestion 3: try to avoid using reverse writing methods such as not exist/no in. If you have to use it, try to choose not exist

Recommendation 4: minimize the use of null processing such as is null/is not null

It is recommended that the value in the IN clause in the 5:SQL statement should not exceed 30

Recommendation 6: for columns in large table queries, conversions such as CAST () or CONVERT () should be avoided as far as possible

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