How to Implement Multi-table non-join queries in mysql

How to Implement Multi-table non-join queries in mysql

Everyone is usingMySQLWhen querying, it is normal to directly query a table, or even join queries for multiple tables. left join and right join are used), inner join, and outer join ). There is a certain relationship between the two tables, that is, we often say there is a foreign key ing, you can use the. id = B. aId statement to write the relationship. This is often used by everyone, but sometimes we need to query two or more tables at the same time, these tables are not correlated, for example, to query some data in the user table and user_history table, this is a non-join query.

In this case, the union all statement is used. For example:

</Pre> <pre class = "html" name = "code"> (select name, sex, age from user where name like 'King % ') union all (select name, sex, age from user_history where name like 'wang % ');

This statement is used to query the information of the User table and all the persons with the surname Wang in the History Table. This operation can also be sorted and intercepted,

(Select name, sex, age from user where name like 'King % ') union all (select name, sex, age from user_history where name like 'King % ') order by age desc limit 0, 50;

This is the person who obtained the first 50 of the two tables by age.

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