i'm getting an errno: 150 when creating a table and this is what i read
from the mysql manual:
"Both tables must be InnoDB type. In the referencing table, there must
be an index where the foreign key columns are listed as the first
columns in the same order. In the referenced table, there must be an
index where the referenced columns are listed as the first columns in
the same order. Index prefixes on foreign key columns are not supported."
I only understand the first statement. Can somebody help me decipher
what the other statements mean especially the following:
"where the referenced columns are listed as the first columns in the
same order"
"Index prefixes on foreign key columns are not supported"
i want to create this table
CREATE TABLE tablename
(
from_domain_nam e ....
from_url_path ...
to_domain_name. ..
to_url_path
PRIMARY KEY(from_domain _name, from_url_path, to_domain_name, to_url_path),
FOREIGN KEY(from_domain _name)
REFERENCES domain(name)
...
...
FOREIGN KEY(from_url_pa th)
REFERENCES url(path)
...
...
FOREIGN KEY(to_domain_n ame)
REFERENCES domain(name)
...
...
FOREIGN KEY(to_url_path )
REFERENCES url(path)
...
...
) ENGINE=InnoDB; 3 1599
- wrote: Can somebody help me decipher what the other statements mean especially the following:
"where the referenced columns are listed as the first columns in the same order"
If you use a composite key for your reference, the fields must be in the
same order in both the referencing and referenced tables.
For example:
create table master (
a int not null,
b int not null,
c int not null,
primary key (a, b, c)
);
create table dependent (
x int,
y int,
z int,
foreign key (x, y, z) references master(a, b, c)
);
But if you make the foreign key reference anything other than (a,b,c),
for example (b,c,a) or (a,b) or (b,c), it can't check against the
primary key in the referenced table. You must list all the fields
listed in the primary key, and in the same order as they are listed in
that primary key definition.
You can mix up the order of the fields in the foreign key, but then they
might be comparing to the wrong fields in the primary key in the other
table:
foreign key (y, z, x) references master(a, b, c)
In this case, y validates against a, z validates against b, and x
validates against c.
What are your primary key definitions in your other tables url and
domain? Do you have compound keys in those tables, and you're trying to
reference them with single-field foreign keys?
"Index prefixes on foreign key columns are not supported"
Index prefixes are for when you have very long string fields, and you
want to index the first N characters, to help reduce the overall size of
the index data structure created. You specify the length N of the
prefix when you create the index, for example:
create index foo on myTable (veryLongVarcha rField(20));
They're saying you can't use that kind of index in foreign keys, for
whatever reason.
Regards,
Bill K.
Bill Karwin wrote: For example:
create table master ( a int not null, b int not null, c int not null, primary key (a, b, c) );
create table dependent ( x int, y int, z int, foreign key (x, y, z) references master(a, b, c) );
somehow i managed to solve the problem by include "INDEX(path )" in the
referenced table. this even works when i removed the TYPE=INNODB
although the manual said it must be an innodb type. will the
constraints work during runtime eventhough it can compile?
- wrote: somehow i managed to solve the problem by include "INDEX(path )" in the referenced table.
Aha, so the path fields in the other tables weren't indexed? That was
definitely your problem.
this even works when i removed the TYPE=INNODB although the manual said it must be an innodb type. will the constraints work during runtime eventhough it can compile?
The constraints will *not* work if you don't make the tables InnoDB.
When you declare a foreign key in a MyISAM table, MySQL accepts the
declaration, but does not enforce the constraint. In other words, you
_are_ permitted to insert values even if they don't occur in the
referenced table.
"In MySQL 3.23.44 and up, InnoDB tables support checking of foreign key
constraints." http://dev.mysql.com/doc/mysql/en/ex...eign-keys.html
Regards,
Bill K. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: Richard Tobin |
last post by:
In a library I am writing, I want to use an errno-like mechanism
for error returns. The error would probably be represented as a
struct rather than just an integer.
I don't have any multi-threaded programs, but others may who want to
use my library. Most likely they'll be using a pthreads-compatible
threads system.
How can I best accommodate them? Presumably they will want the error
object to be in per-thread storage, so to set and...
|
by: Mac |
last post by:
Is it legal to declare errno after you've included errno.h?
For example:
#include<errno.h>
....
int main (void)
{
|
by: Paul Emmons |
last post by:
If I am writing a function that sets errno according to a possible
error condition, should it also set errno to 0 if it executes
normally, or should it leave errno alone on success?
|
by: Vijay Kumar R Zanvar |
last post by:
> In <pan.2004.04.22.04.06.05.969827@bar.net> "Mac" <foo@bar.net> writes:
>
> >Is it legal to declare errno after you've included errno.h?
> >
> >For example:
> >
> >#include<errno.h>
> >
> >...
> >
|
by: pete |
last post by:
On my system, the following five expressions are true:
(HUGE_VAL == HUGE_VAL / 2)
(1 / HUGE_VAL == 0)
(sqrt(HUGE_VAL) == HUGE_VAL)
(sqrt(-1) == HUGE_VAL)
(sqrt(-HUGE_VAL) == HUGE_VAL)
and
| |
by: Urs Beeli |
last post by:
I have a question regarding errno. If I understand it correctly,
including <errno.h> allows me to check "errno" for error values
that some standard library functions may set.
This brings up some questions:
- As I understand it, most functions only set errno in an error
case. I take this to mean, that on success, errno is not
necessarily set to EOK and I would either need to set errno
to EOK before calling the function in question to...
|
by: eyalc1978 |
last post by:
Hi
Does someone knows what does errno 72 means
I got this error when fwriting a structure and still the file is being
created.
I saw something on the net saying that this is caused when trying to
access different file system
|
by: Spiros Bousbouras |
last post by:
Assume I'm writing a function which is going to set
the value of errno if something went wrong but I also
want to guarantee that errno will remain unchanged
if the function completed its task succesfully. So at
the beginning of my code I have something like
int errsto = errno ;
and just before every successful return I have
errno = errsto ;
Is this ok ?
|
by: viza |
last post by:
Hi all,
A quick one - since errno is a lvalue, can I do:
fread( & errno, sizeof errno, 1, fp )
?
TIA
viza
|
by: marktang |
last post by:
ONU (Optical Network Unit) is one of the key components for providing high-speed Internet services. Its primary function is to act as an endpoint device located at the user's premises. However, people are often confused as to whether an ONU can Work As a Router. In this blog post, we’ll explore What is ONU, What Is Router, ONU & Router’s main usage, and What is the difference between ONU and Router. Let’s take a closer look !
Part I. Meaning of...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
| |
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: agi2029 |
last post by:
Let's talk about the concept of autonomous AI software engineers and no-code agents. These AIs are designed to manage the entire lifecycle of a software development project—planning, coding, testing, and deployment—without human intervention. Imagine an AI that can take a project description, break it down, write the code, debug it, and then launch it, all on its own....
Now, this would greatly impact the work of software developers. The idea...
|
by: isladogs |
last post by:
The next Access Europe User Group meeting will be on Wednesday 1 May 2024 starting at 18:00 UK time (6PM UTC+1) and finishing by 19:30 (7.30PM).
In this session, we are pleased to welcome a new presenter, Adolph Dupré who will be discussing some powerful techniques for using class modules.
He will explain when you may want to use classes instead of User Defined Types (UDT). For example, to manage the data in unbound forms.
Adolph will...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: TSSRALBI |
last post by:
Hello
I'm a network technician in training and I need your help.
I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs.
The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols.
I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
|
by: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
| |
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| |