如何将数据插入到涉及外键依赖项的多个表中（MySQL）

Question

I am looking for the best-practice way to insert data to multiple MySQL tables where some columns are foreign key dependencies. Here is an example:

Table: contacts
--------------------------------------------------------------------
|  contact_id  |  first_name  | last_name  |  prof_id  |  zip_code  |
--------------------------------------------------------------------

The 'contacts' table has PRIMARY KEY (contact_id) which simply auto_increments, and FOREIGN KEY (prof_id) REFERENCES 'profession' table, FOREIGN KEY (zip_code) REFERENCES 'zip_code' table. Those tables would look something like this:

Table: profession
----------------------------
|  prof_id  |  profession  |
----------------------------

where 'prof_id' is an INT NOT NULL AUTO_INCREMENT PRIMARY KEY, and

Table: zip_code
--------------------------------
|  zip_code  | city  |  state  |
--------------------------------

where 'zip_code' is an INT(5) NOT NULL PRIMARY KEY.

I have a new person I want to add a record for, let's say:

first_name = 'John', last_name = 'Doe', profession = 'Network Administrator', city = 'Sometown', state = 'NY', zip_code = 12345

---

Here's what I'm trying to do: I want to take that information and insert it into the appropriate tables and columns. To prevent duplicate values in a column (like profession for example) I'd first want to make sure there isn't already an entry for "Network Administrator", and if there was I'd like to just get its key value, if not insert it and then get its key value. The same goes for zip_code, city, state - if it exists just use that zip_code key, otherwise insert the new data and grab the associated key. Then, finally, I'd want to enter the new contact to 'contact' table using the supplied information, including the appropriate key values associated with profession and location from the other tables.

My question is, what is the best recommended way to do this? I know I can sit here and write single statements to check if the given profession exists, if not then enter it, then get the key. Do the same for zip_code. Then finally Insert all of that into contacts, however I know there must be a better way to accomplish this in fewer (perhaps one) statement, especially considering this could cause a problem if, say, the database went offline for a moment in the midst of all of this. Is there a way to use JOINs with this INSERT to essentially have everything cascade into the correct place? Should I look to handle this with a TRANSACTION series of statements?

I am in the learning stage with SQL but I feel that the books and resources I have used thus far have sort of jumped to using nested queries and JOINS under the assumption we have all of these tables of data already populated. I'm even open to suggestions on WHAT I should be Googling to better learn this, or any resources that can help fill this gap. Ideally, I'd love to see some functioning SQL code to do this though. If necessary, assume PHP as the language to interact with the database, but command-line sql is what I was aiming for. Thanks ahead of time, hopefully I made everything clear.

Answer 1

In short, you want to use transactions (more doc on this) so that your inserts are atomic . This is the only way to guarantee that all (or none) of your data will be inserted. Otherwise, you can get into the situation you describe where the database becomes unavailable after some insertions and others are unable to complete. A transaction tells the database that what you are doing is all-or-nothing and so it should roll back if something goes wrong.

When you are using synthetic primary keys, as you are, PHP and other languages provide mechanisms for getting the last inserted id. If you want to do it entirely in MySQL you can use the LAST_INSERT_ID() function. You will end up with code like this:

START TRANSACTION;
INSERT INTO foo (auto,text)
    VALUES(NULL,'text');         # generate ID by inserting NULL
INSERT INTO foo2 (id,text)
    VALUES(LAST_INSERT_ID(),'text');  # use ID in second table
COMMIT;