I have two table Table 1 and Table 2 now I have to create thrid table whose primary key is encoded and combination of table1 and table 2 pk's. I also want to fetch the record of table3 with table 1 and table 2 on the basis of table 3 pk.
can some one help me.
solution in my mind was if I can create some thing similar to JWT toke from the table 1 and table 2 pk's and store it in table 3 pk. but the problems is how I will decode it and perform basic CRUD operation with join query between different tables
Related
I have two tables which I want to fill their corresponding FOREIGN KEYs simultaneously through a TRIGGER at the time of inserting data into customers table:
CREATE TABLE customers (
customer_id SERIAL PRIMARY KEY,
sld_id integer,
customer_name varchar(35)
);
CREATE TABLE slds (
sld_id SERIAL PRIMARY KEY,
customer_id integer,
sld_code varchar(8) UNIQUE
);
ALTER TABLE customers
ADD CONSTRAINT customers_sld_id_fk
FOREIGN KEY (sld_id)
REFERENCES slds(sld_id);
ALTER TABLE slds
ADD CONSTRAINT slds_customer_id_fk
FOREIGN KEY(customer_id)
REFERENCES customers(customer_id);
I have tried to use an AFTER INSERT trigger function, but NEW.customer_id returned NULL.
Then I used BEFORE INSERT which got me the value of NEW.customer_id. However, because of the constraint and the fact that the insertion didn't take place yet the FOREIGN KEY CONSTRAINT is not fulfilled and I get an error.
I have read here that currval() and lastval() can be used but not recommended.
So I created a proxy table to store the generated values. Then, an AFTER INSERT trigger to fill in those fields back in the related tables.
I thought of using a CREATE TEMP TABLE, but found out that it only lasts for the duration of the calling function and not the connection session. Maybe I misunderstood the error message.
Is this a normal efficient practice? Namely, having a dirty table around just to use for such situations.
Or maybe there is another way to achieve this without using a proxy table?
EDITED:
SAMPLE DATA
customersTABLE:
customer_id slds_id customer_name
1 1 johns
3 2 jenn
4 3 thomas
7 4 jeff
8 5 robin
9 6 chris
10 7 larry
slds TABLE:
slds_id slds_code customer_id
1 SL747561 1
2 SL710031 3
3 SL719995 4
4 SL765369 7
5 SL738011 8
6 SL722232 9
7 SL751591 10
EDIT 2:
Forgot to mention that slds_code is generated within a trigger function:
sld_code varchar(8) := 'SL7'||to_char(floor(random() * 100000 + 1)::int, 'fm00000');
What T-SQL DDL is required to create a constraint that ensures that the values in a column in one table are the same as the values in a column in a different table?
I want to do this without using a PK-FK relationship.
The T-SQL DDL at the end of this post is an example of the generic problem that I'm trying to solve.
In this example, I want to know how to add an equality constraint between the two tables that ensures that the set of values in the column:
"PersonMayDriveCar.personName"
is always equal to the set of values in the column
"DriverLicense.personName"
CREATE SCHEMA "Equality Constraint"
GO
CREATE TABLE "Equality Constraint".PersonMayDriveCar
(
carVin nchar(4000) NOT NULL,
personName nchar(70) NOT NULL,
CONSTRAINT PersonMayDriveCar_PK PRIMARY KEY(personName, carVin)
)
GO
CREATE TABLE "Equality Constraint".DriverLicense
(
driverLicenseNr int NOT NULL,
personName nchar(70) NOT NULL,
CONSTRAINT DriverLicense_PK PRIMARY KEY(driverLicenseNr),
CONSTRAINT DriverLicense_UC UNIQUE(personName)
)
GO
I see that you want to maintain referential integrity between the two tables without using a foreign key.
Based on my past experience, I solved such an issue using a trigger.
So you can create a trigger on the DriverLicense table which ensures that any insert or update into the DriverLicense table will be rolled back if the inserted driverLicenseNr doesn't exist in the PersonMayDriveCar table.
You can go through this for a full example:
https://www.mssqltips.com/sqlservertip/4242/sql-server-referential-integrity-without-foreign-keys/
Adhere to convention:
Use an FK. It’s that simple.
Don’t link these table together with an FK, because they are both child tables of ...
Create a person table, which is the parent of the other two tables
Try this:
Person
- id (PK)
- name
- other columns
PersonMayDriveCar
- person_id (FK to person)
- other columns
DriverLicense
- person_id (FK to person)
- other columns
I've here a problem that I couldn't find a proper solution on my researches, maybe it's because I couldn't find out the exact terms to search for it, so if this is a duplicate I will delete it.
My problem is I want to know if it is possible to avoid a combination of data between two fields. I will show the structure and the kind of data I want to avoid. It will be easier to understand.
Table_A Table_B
------------------------ -------------------------------
id integer (PK) id integer (PK)
description varchar(50) title varchar(50)
id1_fromA (FK A->id)
id2_fromA (FK A->id)
I'm trying to validate the following data on table Table_B (combination is between id1_fromA and id2_fromA)
id title id1_fromA id2_fromA
1 Some Title 1 2 --It will be permmited
2 Some other 1 2 --It is a duplicate NOT ALLOWED
3 One more 1 1 --It is equals NOT ALLOWED
4 Another 2 1 --It is same as registry id 1 so NOT ALLOWED
5 Sample data 3 2 --It is ok
With above data I can easily solve the problem for registry ID=2 with
ALTER TABLE table_B ADD CONSTRAINT UK_TO_A_FKS UNIQUE (id1_fromA, id2_fromA);
And the problem for registry ID=3 with
ALTER TABLE table_B ADD CONSTRAINT CHK_TO_A_FKS CHECK (id1_fromA != id2_fromA);
My Problem is with the registry ID=4 I want to avoid such duplicate of combination as 1,2=2,1. Is it possible to do it with a CONSTRAINT or an INDEX or an UNIQUE or I will need to create a trigger or a procedure to do so?
Thanks in advance.
You can't do this with a unique constraint, but you can do this with a unique index.
create unique index UK_TO_A_FKS
on table_b (least(id1_froma, id2_froma), greatest(id1_froma, id2_froma));
I need to keep 3 columns in 2 different tables synchronized.
MS SQL Server 2008
create table a(
id int IDENTITY(1,1),
name1 nvarchar(255),
name2 nvarchar(255),
date1 date default null,
date2 date default null,
...
CONSTRAINT pk primary key (id),
CONSTRAINT uniqueNames UNIQUE (name1,name2))
I'm looking to create another table that will duplicate the first 3 columns in my second table, and keep them up to date (insert, delete, update). I was looking at triggers, but the consensus seems to be that if I insert or update multiple rows at once, this will not execute correctly. Any idea's on how to accomplish this?
Ideally you would normalise the data by moving the duplicated fields in to another table and referencing them via a foreign key.
However triggers could also be used to solve this problem. take a look here : How to write trigger for multiple row update?
hai guys,
i am planning to create a table view and the detail view for the corresponding row, all the datas are fetch from the sqlite database. For this i have created two tables in the database table one for the datas in the table view list and table two for the detail view of the table list. i set the product id as the primary key for the table one. i want the product id as the foreign key for table two. i don't know how to set the foreign key for it and don't know how to retrieve from the table two and display it in the detail view. please help me to do this.
Thanks in advance...
1.Change your DB Settings enable to Foreign Keys.
2.Create the child table like this
table1 is the parent table having id1 as primary key.
CREATE TABLE "table1" ("id1" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL)
table2 is the child table having id2 as a foreign key with reference to id1 of table1.
CREATE TABLE table2 (
id2 INTEGER,
parent_id INTEGER,
description TEXT,
FOREIGN KEY (id2) REFERENCES table1(id1)
)
Use equijoin to retrieve the data from the tables.
select * from table1,table2 where table1.id1=table2.id2;
or
select table2.* from table2,table1 where table1.id1=table2.id2;
to retrieve the data from single table alone.
Hope this helps to you!