Foreign Key Constraints

Actually, I think I figured it out. I had altered the foreign key within
config to it's current condition, but config_values still existed. I guess
there was some data stored somewhere that kept assuming (for config_values)
that config tag was using just ONE column as its foreign key? Or maybe I
have no idea what I'm talking about. That's probably it. :)

When I deleted, and then recreated config_values, and then also config, it
worked.

Anyone have any explanations?

joemono

"joemono" <montero7@msu.edu> wrote in message
news:afhubr$2k5b$1@msunews.cl.msu.edu...

Hi,
I'm trying to understand foreign key constraints more, but having a heck

of

a time doing so. I've been looking through Google groups to try to find
answers to the problems I'm having, but I haven't come across any as of

yet.

Here is the situation:

I have a table of configurations. The config table has config_tag,
config_value columns. I also have a table of config_values, ones that are
valid for the config table. The config_values table has all the possible
configurations (only about 40 or so) that can be put into the config

table.

Currently, the config_values table has as its primary key (tag, value),

and

the config table has as a foreign key (config_tag, config_value) which
references config_values (tag, value). I've also messed around with match
full, but I'm not sure I understand it completely, and it hasn't solved

the

problem I'm having yet.

I'm adding some new options, and so I added rows to the config_values

table,

with completely new tags, but with values that other tags also use. (I'm
expanding existing options to cover other areas of the project). Now that
the rows are in the config_values table, I've decided to change them

around,

and use different values, so I want to delete them. However, I keep

getting:

simple possible explanation:

you have a parent table and child table.

foreign key in parent table references values in child table.

you can only insert values in the field in the parent table that exist in
the child table.

to delete values in the child table you must also remove all rows in the
parent table that reference that value which is where your problem exisited
i think.

Steve

joemono wrote:

Actually, I think I figured it out. I had altered the foreign key within
config to it's current condition, but config_values still existed. I guess
there was some data stored somewhere that kept assuming (for config_values)
that config tag was using just ONE column as its foreign key? Or maybe I
have no idea what I'm talking about. That's probably it. :)

When I deleted, and then recreated config_values, and then also config, it
worked.

Anyone have any explanations?

Well,

you've setup a 2 column foreign key exactly as it should be to ensure
that the config table can only hold possible value combinations that
exist in config_values. What happened was that you cannot change
config_values as long as rows in config actually reference them.

If you specify ON UPDATE CASCADE, then you can change config_values and
referencing rows in config will automatically be updated as well. Would
that make sense to you?

Jan

joemono

"joemono" <montero7@msu.edu> wrote in message
news:afhubr$2k5b$1@msunews.cl.msu.edu...

Hi,
I'm trying to understand foreign key constraints more, but having a heck

of

a time doing so. I've been looking through Google groups to try to find
answers to the problems I'm having, but I haven't come across any as of

yet.

Here is the situation:

I have a table of configurations. The config table has config_tag,
config_value columns. I also have a table of config_values, ones that are
valid for the config table. The config_values table has all the possible
configurations (only about 40 or so) that can be put into the config

table.

Currently, the config_values table has as its primary key (tag, value),

and

the config table has as a foreign key (config_tag, config_value) which
references config_values (tag, value). I've also messed around with match
full, but I'm not sure I understand it completely, and it hasn't solved

the

problem I'm having yet.

I'm adding some new options, and so I added rows to the config_values

table,

with completely new tags, but with values that other tags also use. (I'm
expanding existing options to cover other areas of the project). Now that
the rows are in the config_values table, I've decided to change them

around,

and use different values, so I want to delete them. However, I keep

getting:

"fk_config referential integrity violation - key in config_values still
referenced from config"

Like I said, I've been trying the match full option, because it only makes
sense to match the config_tag-config_value combination, since many of the
values have the same...value. Right?

Anyway, I hope this makes sense. Any help is greatly appreciated!

joemono

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