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In mysql, you can use the UNION operator to achieve the effect of merging results after a query. The function of this operator is to join the results of more than two SELECT statements into a result set. The syntax is "SELECT query statement 1 UNION [ALL] SELECT query statement 2".

The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.

How to query and merge with mysql

The MySQL UNION operator is used to join the results of more than two SELECT statements into a result set. Multiple SELECT statements delete duplicate data.

Grammar

MySQL UNION operator syntax format:

SELECT expression1, expression2,... Expression_nFROM tables [WHERE conditions] UNION [ALL | DISTINCT] SELECT expression1, expression2,... Expression_nFROM tables [WHERE conditions]

Parameters.

Expression1, expression2,... Expression_n: the column to retrieve.

Tables: the data table to retrieve.

WHERE conditions: optional, search condition.

DISTINCT: optionally, delete duplicate data in the result set. By default, the UNION operator has removed duplicate data, so the DISTINCT modifier has little effect on the result.

ALL: optional, returns all result sets, including duplicate data.

Examples are as follows:

Query the information of all fruits whose prices are less than 9, query the information of all fruits whose s_id is equal to 101,103, and use UNION to connect the query results. The SQL statement is as follows:

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