How to Efficiently Intersect Data from Multiple Tables in MySQL?

Intersecting Data in MySQL

Issue:

In MySQL, a user requires a method to intersect data from two tables, "records" and "data," based on multiple fields in the "records" table. A previous example using INTERSECT in another DBMS returned unsatisfactory results.

Solution:

MySQL does not provide direct support for the INTERSECT operator. However, there are alternative approaches to achieve the desired functionality.

One option is to use an inner join:

SELECT DISTINCT records.id 
FROM records
INNER JOIN data d1 on d1.id = records.firstname AND d1.value = "john"
INNER JOIN data d2 on d2.id = records.lastname AND d2.value = "smith"

This query joins the "records" table with two instances of the "data" table, filtering for rows that have matching values in both joins.

Another alternative is an in clause:

SELECT DISTINCT records.id 
FROM records
WHERE records.firstname IN (
    select id from data where value = 'john'
) AND records.lastname IN (
    select id from data where value = 'smith'
)

This approach selects rows from the "records" table whose "firstname" and "lastname" fields match values in the "data" table.

These methods provide effective ways to intersect data in MySQL by combining rows from multiple tables based on common criteria.

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