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Editorial Team
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Asked: 2026-05-26T20:44:19+00:00

I want to be able to insert data into t1 and have data get

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I want to be able to insert data into t1 and have data get populated in table t2 with the primary key as a foreign key in t2.

Basically, how come in my current setup when I INSERT INTO t1 (first_name, last_name) values ( "blah", "blah"); and then do SELECT * FROM t2; t2 it says Empty Set (0.00 sec) for t2? Shouldn’t it at least show the default id of 1?

t1:

+------------+------------------+------+-----+---------+----------------+
| Field      | Type             | Null | Key | Default | Extra          |
+------------+------------------+------+-----+---------+----------------+
| first_name | varchar(20)      | NO   |     | NULL    |                |
| last_name  | varchar(20)      | NO   |     | NULL    |                |
| id         | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
+------------+------------------+------+-----+---------+----------------+

t2:

+-----------+------------------+------+-----+---------+-------+
| Field     | Type             | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| address   | varchar(50)      | NO   |     | NULL    |       |
| id        | int(10) unsigned | NO   | MUL | NULL    |       |
| last_name | varchar(20)      | YES  |     | NULL    |       |
+-----------+------------------+------+-----+---------+-------+
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1 Answer

  1. Editorial Team

    In a relational database, a FOREIGN KEY is a declaration that you intend to insert values into T2 that must match an already existing value in T1, and that you want the database to refuse to perform any action that would break this relationship.

    It does not mean that the database will create records on its own in order to satisfy a relationship. If you try to insert a value into T2 that does not exist in T1, the command will fail; it will not add the required record to T1.

    That is the opposite of what you’re suggesting, however, in which you want the foreign key values to get automatically generated. However, there’s no requirement that a primary key value actually have references and, furthermore, no limit on the number of times that primary key value can be referenced — so how would the database guess what should be created in T2?

    That said, if you want some of your own code to execute automatically when data is added to T1, code which can do whatever you want, you can create a trigger on T1.

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