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

In this issue, the editor will bring you about how to insert non-duplicate data in MySQL. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

Previously, the most naive idea is to query the record to be inserted first. If the result set size is greater than 0, the data already exists, and no data insertion operation is carried out, otherwise insert into. Today, I realized that the problem can be solved with a SQL statement, using the dual table of MySQL, as follows:

INSERT INTO users_roles

(userid, roleid)

SELECT 'userid_x',' roleid_x'

FROM dual

WHERE NOT EXISTS (

SELECT * FROM users_roles

WHERE userid = 'userid_x'

AND roleid = 'roleid_x'

);

Where users_roles is the table that needs to be inserted, and userid_x and roleid_x are records that need to be inserted.

The dual table in MySQL is explained as follows:

Table-`dual`: a dummy table in

Interpretation of the dual table in the mysql document:

You are allowed to specify DUAL as a dummy table name in situations where no tables are referenced:

Mysql > SELECT 1 + 1 FROM DUAL

-> 2

DUAL is purely for the convenience of people who require that all SELECT statements should have FROM and possibly other clauses. MySQL may ignore the clauses. MySQL does not require FROM DUAL if no tables are referenced.

The above is how to insert non-duplicate data into the MySQL shared by the editor. If you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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