I have a simple problem. How can I add a unique constraint for a table, without relating the values to their columns? For example, I have this table
ID_A ID_B
----------
1 2
... ...
In that example, I have the record (1,2). For me, (1,2) = (2,1). So i don't want to allow my database to store both values. I know I can accomplish it using, triggers or checks and functions. But i was wondering if there is any instruccion like
CREATE UNIQUE CONSTRAINT AS A SET_CONSTRAINT
You could write a view like that:
select 1 as Dummy
from T t1
join T t2 on t1.ID1 = t2.ID2 AND t1.ID2 = t2.ID1 --join to corresponding row
cross join TwoRows
And create a unique index on Dummy. TwoRows is a table that contains two rows with arbitrary contents. It is supposed to make the unique index fail if there ever is a row in it. Any row in this view indicates a uniqueness violation.
You can do this using Instead of Insert trigger.
Demo
Table Schema
CREATE TABLE te(ID_A INT,ID_B INT)
INSERT te VALUES ( 1,2)
Trigger
Go
CREATE TRIGGER trg_name
ON te
instead OF INSERT
AS
BEGIN
IF EXISTS (SELECT 1
FROM inserted a
WHERE EXISTS (SELECT 1
FROM te b
WHERE ( ( a.id_a = b.id_b
AND a.id_b = b.id_a )
OR ( a.id_a = b.id_a
AND a.id_b = b.id_b ) )))
BEGIN
PRINT 'duplciate record'
ROLLBACK
END
ELSE
INSERT INTO te
SELECT Id_a,id_b
FROM inserted
END
SELECT * FROM te
Insert Script
INSERT INTO te VALUES (2,1) -- Duplicate
INSERT INTO te VALUES (1,2) --Duplicate
INSERT INTO te VALUES (3,2) --Will work
Related
Sample data:
CREATE TABLE Departments (
Code INTEGER PRIMARY KEY,
Name varchar(255) NOT NULL ,
Budget decimal NOT NULL
);
CREATE TABLE Employees (
SSN INTEGER PRIMARY KEY,
Name varchar(255) NOT NULL ,
LastName varchar(255) NOT NULL ,
Department INTEGER NOT NULL ,
foreign key (department) references Departments(Code)
)
INSERT INTO Departments(Code,Name,Budget) VALUES(14,'IT',65000);
INSERT INTO Departments(Code,Name,Budget) VALUES(37,'Accounting',15000);
INSERT INTO Departments(Code,Name,Budget) VALUES(59,'Human Resources',240000);
INSERT INTO Departments(Code,Name,Budget) VALUES(77,'Research',55000);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('123234877','Michael','Rogers',14);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('152934485','Anand','Manikutty',14);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('222364883','Carol','Smith',37);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('326587417','Joe','Stevens',37);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('332154719','Mary-Anne','Foster',14);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('332569843','George','O''Donnell',77);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('546523478','John','Doe',59);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('631231482','David','Smith',77);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('654873219','Zacary','Efron',59);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('745685214','Eric','Goldsmith',59);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('845657245','Elizabeth','Doe',14);
INSERT INTO Employees(SSN,Name,LastName,Department) VALUES('845657246','Kumar','Swamy',14);
Problem: "Select the names of departments with more than two employees."
Wikibooks solution:
/*With subquery*/
SELECT D.Name FROM Departments D
WHERE 2 <
(
SELECT COUNT(*)
FROM Employees
WHERE Department = D.Code
);
My question: How does this solution work? That is, how does MSSQL know which values in Departments are to be kept from the sub-query? I can't see any way that the condition WHERE Department = D.Code can return a result that is ordered in a useful way to the outer query. I don't think that this is a fluke, I think that I just don't understand how SQL is vectorised.
This is called a correlated subquery.
That is to say, the inner query is correlated to the outer one by use of an outer reference. In this case, that is D.Code. Therefore the subquery is being calculated for every row of D.
It's not a matter of ordering, in fact this query can return results in any order. But the result from the subquery must be greater than 2 otherwise the WHERE predicate fails.
SELECT D.Name FROM Departments D -- Departments has been aliased as D
WHERE 2 <
(
SELECT COUNT(*)
FROM Employees
WHERE Department = D.Code -- Here the inner query is being limited by
-- the reference to the outer D table
);
I would probably use ... > 2 rather than 2 < ...
Side point: It's better to always use an explicit table reference in subqueries, eg e.Department = D.Code, because otherwise you could misspell a column and end up referring to an outer column instead of an inner column, and the correlation wouldn't work properly
I have a table named MarketData, and I am trying to pull certain columns from MarketData and insert them to another table called Payups. But I only want to insert data that doesn't repeat onto Payups.
Keep in mind, the MarketData table includes more columns that I don't need in the PayUps column.
After I execute the query below, it keeps on adding records that are similar.
INSERT INTO [MortgagePipeline].[dbo].[PayUps]
(
RecordDate
,Investor
,Product
,MinCoupon
,[Payup(bcp)]
)
SELECT DISTINCT t1.ContractDate
,t1.SourceCode
,t1.ProductName
,t1.ContractInterestRate
,t1.ContractPrice
FROM [MortgagePipeline].[dbo].[MarketData] t1
WHERE NOT EXISTS
(
SELECT RecordDate
,Investor
,Product
,MinCoupon
,[Payup(bcp)]
FROM [MortgagePipeline].[dbo].[PayUps] t2
WHERE t2.RecordDate = t1.ContractDate
AND t2.Investor = t1.SourceCode
AND t2.Product = t1.ProductName
AND t2.MinCoupon = t1.ContractInterestRate
AND t2.[Payup(bcp)] = t1.ContractPrice
AND t2.MaxCoupon = NULL
AND t2.PayupName = NULL
)
RecordDate, Investor , Product ,MinCoupon ,[Payup(bcp)], MaxCoupon PayupName are all the columns that exists on Payups. all of The values of those columns are inserted from the MarketData Table except from MaxCoupon and PayupName that remain null.
I have one table (Table1) that has several columns used in combination: Name, TestName, DevName, Dept. When each of these 4 columns have values, the record is inserted into Table2. I need to confirm that all of the records with existing values in each of these fields within Table1 were correctly copied into Table 2.
I have created a query for it:
SELECT DISTINCT wr.Name,wr.TestName, wr.DEVName ,wr.Dept
FROM table2 wr
where NOT EXISTS (
SELECT NULL
FROM TABLE1 ym
WHERE ym.Name = wr.Name
AND ym.TestName = wr. TestName
AND ym.DEVName = wr.DEVName
AND ym. Dept = wr. Dept
)
My counts are not adding up, so I believe that this is incorrect. Can you advise me on the best way to write this query for my needs?
You can use the EXCEPT set operator for this one if the table definitions are identical.
SELECT DISTINCT ym.Name, ym.TestName, ym.DEVName, ym.Dept
FROM table1 ym
EXCEPT
SELECT DISTINCT wr.Name, wr.TestName, wr.DEVName, wr.Dept
FROM table2 wr
This returns distinct rows from the first table where there is not a match in the second table. Read more about EXCEPT and INTERSECT here: https://learn.microsoft.com/en-us/sql/t-sql/language-elements/set-operators-except-and-intersect-transact-sql?view=sql-server-2017
Your query should do the job. It checks anything that are in Table1, but not Table2
SELECT ym.Name, ym.TestName, ym.DEVName, ym.Dept
FROM Table1 ym
WHERE NOT EXISTS (
SELECT 1
FROM table2
WHERE ym.Name = Name AND ym.TestName = TestName AND ym.DEVName = DEVName AND ym. Dept = Dept
)
If the structure of both tables are the same, EXCEPT is probably simpler.
IF OBJECT_ID(N'tempdb..#table1') IS NOT NULL drop table #table1
IF OBJECT_ID(N'tempdb..#table2') IS NOT NULL drop table #table2
create table #table1 (id int, value varchar(10))
create table #table2 (id int)
insert into #table1(id, value) VALUES (1,'value1'), (2,'value2'), (3,'value3')
--test here. Comment next line
insert into #table2(id) VALUES (1) --Comment/Uncomment
select * from #table1
select * from #table2
select #table1.*
from #table1
left JOIN #table2 on
#table1.id = #table2.id
where (#table2.id is not null or not exists (select * from #table2))
I have 2 tables
Table A
Column A1 Column A2 and
Table B
Column B1 Column B2
Column A1 is not unique and not the PK, but I want to put a constraint on column B1 that it cannot have values other than what is found in Column A1, can it be done?
It cannot be done using FK. Instead you can use a check constraint to see if B value is available in A.
Example:
alter table TableB add constraint CK_BValueCheck check dbo.fn_ValidateBValue(B1) = 1
create function dbo.fn_ValidateBValue(B1 int)
returns bit as
begin
declare #ValueExists bit
select #ValueExists = 0
if exists (select 1 from TableA where A1 = B1)
select #ValueExists = 1
return #ValueExists
end
You can not have dynamic constraint to limit the values in Table B. Instead you can either have trigger on TableB or you need to limit all inserts or updates on TbaleB to select values from Column A only:
Insert into TableB
Select Col from Table where Col in(Select ColumnA from TableA)
or
Update TableB
Set ColumnB= <somevalue>
where <somevalue> in(Select columnA from TableA)
Also, I would add its a very design practice and can not guarantee accuracy all the time.
Long way around but you could add an identity to A and declare the PK as iden, A1.
In B iden would just be an integer (not identity).
You asked for any other ways.
Could create a 3rd table that is a FK used by both but that does not assure B1 is in A.
Here's the design I'd go with, if I'm free to create tables and triggers in the database, and still want TableA to allow multiple A1 values. I'd introduce a new table:
create table TableA (ID int not null,A1 int not null)
go
create table UniqueAs (
A1 int not null primary key,
Cnt int not null
)
go
create trigger T_TableA_MaintainAs
on TableA
after insert, update, delete
as
set nocount on
;With UniqueCounts as (
select A1,COUNT(*) as Cnt from inserted group by A1
union all
select A1,COUNT(*) * -1 from deleted group by A1
), CombinedCounts as (
select A1,SUM(Cnt) as Cnt from UniqueCounts group by A1
)
merge into UniqueAs a
using CombinedCounts cc
on
a.A1 = cc.A1
when matched and a.Cnt = -cc.Cnt then delete
when matched then update set Cnt = a.Cnt + cc.Cnt
when not matched then insert (A1,Cnt) values (cc.A1,cc.Cnt);
And test it out:
insert into TableA (ID,A1) values (1,1),(2,1),(3,2)
go
update TableA set A1 = 2 where ID = 1
go
delete from TableA where ID = 2
go
select * from UniqueAs
Result:
A1 Cnt
----------- -----------
2 2
Now we can use a genuine foreign key from TableB to UniqueAs. This should all be relatively efficient - the usual FK mechanisms are available between TableB and UniqueAs, and the maintenance of this table is always by PK reference - and we don't have to needlessly rescan all of TableA - we just use the trigger pseudo-tables.
I have two tables with more than 800 rows in each.Table names are 'education' and 'sanitation'.The column name 'ID' is common in both the tables.Now i want to join these both tables as full outer join and i want to save the results of this table as a new table.I can join it very easily,But how to save those data's as a new table.Please help Me.
select * into bc from education e join sanitation s on e.id=s.id
I have around 30 columns in each table.So i can not explicitly create table schema for a new table.
I want all the columns from both tables.I have 20 tables with each 800 rows.From this 20 tables i want to make one master table taking 'ID' as primary key in all.
Sample Code:
Table one:
create table dummy1(
id int , fname varchar(50)
)
insert into dummy1 (id,fname) values (1,'aaa')
insert into dummy1 (id,fname) values (2,'bbb')
insert into dummy1 (id,fname) values (3,'ccc')
insert into dummy1 (id,fname) values (3,'ccc')
Table Two
create table dummy2(
id int , lname varchar(50)
)
insert into dummy2 (id,lname) values (1,'abc')
insert into dummy2 (id,lname) values (2,'pqr')
insert into dummy2 (id,lname) values (3,'mno')
Now Create new table 3
create table dummy3(
id int , fname varchar(50),lname varchar(50)
)
Insert Query for table 3 look like
insert into dummy3 (id,fname,lname)
(select a.id,a.fname,b.lname from dummy1 a inner join dummy2 b on a.id=b.id)
Table 3 will contain table1, table2 data
Follow below:
SELECT t1.Column1, t2.Columnx
INTO DestinationTable
FROm education t1
INNER JOIN sanitation t2 ON t1.Id = t2.Id
EDIT:
SELECT * will not work for you because you have a column ID which exists in both the tables. So the above solution will work you.
EDIT:
1- You can temporarily rename the Id column in one table, then try
2- SELECT *
INTO DestinationTable
FROm education t1
INNER JOIN sanitation t2 ON t1.Id = t2.Id
3- Revert the column name back to Id.