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HeckDan
Asked: 2020-05-24 17:15:45 +0800 CST 2020-05-24 17:15:45 +0800 CST

Using INNER JOINs with USING, ON or WHERE ( where table.column )

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I have learned USING by doing things like this:

SELECT nufactura,des,cantidadc,precio,precio*cantidadc AS "SUBTOTAL"
FROM `facturas` INNER JOIN `fac_pro` USING(nufactura)INNER JOIN `productos` USING(codigop)
WHERE nufactura = "700" 
ORDER BY cantidadc DESC

but I haven't really understood its order very well or why it is like that, much less the use with ON and WHERE and that call with nombre.nombre1.That point I don't really know what it does. Is it the same as FROM ? Is it like a pointer or something?

sql

1 Answers

  1. Best Answer

    When you concatenate 2 tables you need to indicate which fields are the ones that relate the tables.

    Normally ON is used by default:

    SELECT * FROM T1 INNER JOIN T2 ON T1.id_t2 = T2.id

    In some cases the names of the tables are the same, for this a shortcut is to use USING Suppose that T1 has a field called id_foo the same as T2 that also has a field called id_foo that relates them.

    You can use the ON normally:

    SELECT * FROM T1 INNER JOIN T2 ON T1.id_foo = T2.id_foo

    Or just use the USING:

    SELECT * FROM T1 INNER JOIN T2 USING(id_foo)
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