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This article will explain in detail what it means to write "1" 1 after the where condition in the SQL sentence. The editor thinks it is very practical, so I share it with you as a reference. I hope you can get something after reading this article.

This code should be generated by the program (for example, Java), and the conditions after 1 to 1 in the where condition are dynamically changed through the if block. For example:

String sql= "select * from table_name where 1: 1"; if (conditon 1) {sql=sql+ "and var2=value2";} if (conditon 2) {sql=sql+ "and var3=value3";} where 1: 1 is to avoid syntax errors caused by the first word after the where keyword, which is directly "and".

Connection AND condition in dynamic SQL

Where 1 is designed to avoid syntax errors caused by the first word after the where keyword, which is directly "and".

There must always be a statement after where, and adding 1: 1 ensures that the syntax will not go wrong!

Select * from table where 1

Because there is no field named 1 in table, the SQL is equivalent to select * from table

This SQL statement is obviously a full table scan, which requires a lot of IO operations, and the larger the amount of data, the slower it is.

It is suggested to add the required input items when querying, that is, to add some commonly used required conditions after where 1, and to index these necessary conditions properly, the efficiency will be greatly improved.

Copy table create table table_nameas select * from Source_tablewhere 1x1

Copy table structure

Create table table_nameas select * from Source_table where 1 1

This is the end of the article on "what does it mean to write" after the where condition in the SQL sentence? I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, please share it for more people to see.

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