I am new to postgresql..I am creating a database which contains table “user” with columns “Name”,”Sum”,”id”(which is a serial primary key)
I want to input data only in columns Name and Sum since id is a serial PK
The column “id” is a foreign key in another table “account”, so when I am trying to input data in the table it is telling me I am violating the foreign key constraint
Here is the code:
INSERT INTO public.”user”(“Name”,”Sum”)
VALUES (‘Tasneem’,400);
It is telling me
Insert or update on table “user” violates foreign key constraint “user_Sum_fkey”
Key (Sum)=(400) is not present in table account
Related
I'm using PostgreSQL.
I have a table accounts with account_id as the primary key. I also have a second table called relations with a composite primary key (follower_id, following_id). Each relation must be unique.
ALTER TABLE accounts ADD CONSTRAINT users_pk PRIMARY KEY (account_id);
ALTER TABLE relations ADD CONSTRAINT relations_pk PRIMARY KEY (follower_id, following_id);
I want to create a foreign key constraint from follower_id (relations) -> account_id (accounts), and the same with following_id.
ALTER TABLE relations ADD CONSTRAINT follower_id_fk FOREIGN KEY (follower_id) REFERENCES accounts (account_id) ON DELETE CASCADE
This foreign key is not accepted by the database. I get the following error:
ERROR: insert or update on table "relations" violates foreign key constraint "follower_id_fk"
DETAIL: Key (follower_id)=(4) is not present in table "accounts".
I understand this, because it's a composite primary key.
What I want to achieve:
When an account is deleted, I want to delete all the records where the account_id is the follower_id (ON DELETE CASCADE) AND where it is the following_id.
I could do this in my nodejs code or with a trigger function, but I don't know what will be the best performance-wise. Does anyone knows a/the best solution?
I have a table user_type and user_type_id is the primary key of that table and I have another table user_details where user_type_id is a reference of the foreign key.
I want to change the id value of the user_type_id column.
First update user_details to set the foreign key column to NULL for the rows that depend on the primary key, then update user_type, then change the rows in user_details to the updated value.
You can make this easier in two ways:
define the foreign key with ON UPDATE CASCADE, then this happens automatically
define the foreign key as DEFERRABLE, the you can defer the check to the end of the transaction
I'm creating a database in PostgreSQL and want to include a many-to-many relationship between the tables. The two tables I want to include are as follows:
CREATE TABLE "meter" (
"id" integer PRIMARY KEY,
"nmi" integer,
"next_scheduled_read_date" timestamp
);
CREATE TABLE "register" (
"id" text PRIMARY KEY,
"value" text
);
The many-to-many relationship I want to have is between meter id and register id. I have then created the junction table below:
CREATE TABLE "meter_registers" (
"meter_id" integer NOT NULL,
"register_id" text NOT NULL,
PRIMARY KEY ("meter_id", "register_id"),
FOREIGN KEY ("meter_id") REFERENCES "meter" ("id") ON UPDATE CASCADE,
FOREIGN KEY ("register_id") REFERENCES "register" ("id") ON UPDATE CASCADE
);
I then want to create a table that references the meter_id and register_id values from the junction table above which is structured as follows:
CREATE TABLE "demand_data" (
"upload_id" integer PRIMARY KEY,
"nmi" integer,
"meter" integer,
"register" text,
"start" timestamp,
"end" timestamp,
"duration" Time,
"demand" double precision
);
Where the meter and register reference the corresponding junction table columns. However, as the values of the junction table will not be unique I can't simply add a foreign key for the meter and register columns so I run into an error when I run the following:
ALTER TABLE "demand_data" ADD FOREIGN KEY ("meter") REFERENCES "meter_registers" ("meter_id");
ALTER TABLE "demand_data" ADD FOREIGN KEY ("register") REFERENCES "meter_registers" ("register_id");
ERROR: there is no unique constraint matching given keys for referenced table "meter_registers"
Is there a way to possibly reference the junction table columns in the demand_data table without the foreign key constraint? I know it's possible to do with a separate query once some data has been added using inner joins however, is it possible to do it through database table set up?
Yes. A compound foreign key.
ALTER TABLE "demand_data"
ADD FOREIGN KEY ("meter","register")
REFERENCES "meter_registers"( "meter_id", "register_id");
Note: Not directly related you should avoid those dreaded double quotes.
If demand_data references meter_registers, it should reference its primary key. So add a single foreign key constraint on both columns.
If you want two separate foreign keys,you should probably reference meter and register directly.
I've got an existing table of dogs which I would like to partition by list using the colour column:
CREATE TABLE dogs (
id int PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
colour text,
name text
)
;
Because it's not possible to partition an existing table, I'm going to make a new empty partitioned table then copy the data across.
CREATE TABLE
trade_capture._customer_invoice
(
LIKE
trade_capture.customer_invoice
INCLUDING ALL
)
PARTITION BY LIST (bill_month)
;
This reports:
ERROR: insufficient columns in PRIMARY KEY constraint definition
DETAIL: PRIMARY KEY constraint on table "_dogs" lacks column "colour" which is part of the partition key.
I know I can ignore the primary key like this, but it seems bad to have a table with no primary key!
CREATE TABLE
_dogs
(
LIKE
dogs
INCLUDING ALL
EXCLUDING INDEXES
)
PARTITION BY LIST (colour)
;
What's the best way to proceed so I have a partitioned table which still has a primary key?
Add the partitioning key to the primary key:
ALTER TABLE trade_capture._customer_invoice
ADD PRIMARY KEY (id, bill_month);
There is no other option to have a unique constraint on a partitioned table.
When trying to ALTER TABLE in Postgres 9.5 to create foreign key constraint: from product_template.product_brand_id to product_brand.id
ALTER TABLE public.product_template
ADD CONSTRAINT product_template_product_brand_id_fkey
FOREIGN KEY (product_brand_id)
REFERENCES public.product_brand (id) MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE SET NULL;
Returns error
ERROR: insert or update on table "product_template" violates foreign key constraint "product_template_product_brand_id_fkey"
DETAIL: Key (product_brand_id)=(12) is not present in table "product_brand".
STATEMENT: ALTER TABLE "product_template" ADD FOREIGN KEY ("product_brand_id") REFERENCES "product_brand" ON DELETE set null
Im confused why postgres is trying to find product_brand.product_brand_id, when the fkey is from product_template.product_brand_id to product_brand.id
Any ideas?
The error message simply states that there is at least one row in the table product_template that contains the value 12 in the column product_brand_id
But there is no corresponding row in the table product_brand where the column id contains the value 12
Key (product_brand_id)=(12) relates the source column of the foreign key, not the target column.
In simple terms, the value of FOREIGN KEY(product_brand_id) provided in your ALTER statement is not present in the source (product_brand) table.