I have a table with data, and I want to change some column to unique, it must to be unique, but I'm worried about have duplicated data in that column and it brings some problems to my database.
I want to know what happen if I change a column to unique that doesn't have unique data, I'll lost some records, just got an error message, or something else?
PS.: I'm using SQL Server
Thanks in advance.
You just won't be able to add a UNIQUE constraint on a COLUMN with duplicates datas.
In SSMS, the error message is something like that
The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name 'dbo.<Table>' and the index name '<constraintname>'. The duplicate key value is (<NULL>).
Could not create constraint. See previous errors.
So you can be quiet, you won't lose any data.
alter table YourTable add constraint UX_YourTable_YourColumn unique(YourColumn)
If there is duplicate data, the alter will abort without making any changes.
You can query duplicates like:
select YourColumn
, count(*) as DuplicateCount
from YourTable
group by
YourColumn
having count(*) > 1
Related
I am adding a column as a foreign key which cannot be NULL and so need to have a DEFAULT value.
ALTER TABLE location
ADD [retailer_brand_id] INT NOT NULL DEFAULT (SELECT retailer_id from retailer),
FOREIGN KEY(retailer_brand_id) REFERENCES retailer_brand(retailer_brand_id);
What I want to achieve is, get the retailer_id from SELECT retailer_id from retailer and if it is equal to 12 then set it to 0, otherwise set to the retailer_id returned by the select query.
When I use the above query, I get an error message
Subqueries are not allowed in this context. Only scalar expressions are allowed.
I recommend a calculated column instead....so you don't also have to have this case statement in application logic as well as the table definition...don't want it in 2 spots...and don't have to worry about when retailerid changes...calc column would take care of that
I needed similar functionality. Calculated column is not an option for me, since my value should be changeble later by user, so I went with trigger on insert.
Described for example here: Trigger to update table column after insert?
I want to add another row in my existing table and I'm a bit hesitant if I'm doing the right thing because it might skew the database. I have my script below and would like to hear your thoughts about it.
I want to add another row for 'Jane' in the table, which will be 'SKATING" in the ACT column.
Table: [Emp_table].[ACT].[LIST_EMP]
My script is:
INSERT INTO [Emp_table].[ACT].[LIST_EMP]
([ENTITY],[TYPE],[EMP_COD],[DATE],[LINE_NO],[ACT],[NAME])
VALUES
('REG','EMP','45233','2016-06-20 00:00:00:00','2','SKATING','JANE')
Will this do the trick?
Your statement looks ok. If the database has a problem with it (for example, due to a foreign key constraint violation), it will reject the statement.
If any of the fields in your table are numeric (and not varchar or char), just remove the quotes around the corresponding field. For example, if emp_cod and line_no are int, insert the following values instead:
('REG','EMP',45233,'2016-06-20 00:00:00:00',2,'SKATING','JANE')
Inserting records into a database has always been the most common reason why I've lost a lot of my hairs on my head!
SQL is great when it comes to SELECT or even UPDATEs but when it comes to INSERTs it's like someone from another planet came into the SQL standards commitee and managed to get their way of doing it implemented into the final SQL standard!
If your table does not have an automatic primary key that automatically gets generated on every insert, then you have to code it yourself to manage avoiding duplicates.
Start by writing a normal SELECT to see if the record(s) you're going to add don't already exist. But as Robert implied, your table may not have a primary key because it looks like a LOG table to me. So insert away!
If it does require to have a unique record everytime, then I strongly suggest you create a primary key for the table, either an auto generated one or a combination of your existing columns.
Assuming the first five combined columns make a unique key, this select will determine if your data you're inserting does not already exist...
SELECT COUNT(*) AS FoundRec FROM [Emp_table].[ACT].[LIST_EMP]
WHERE [ENTITY] = wsEntity AND [TYPE] = wsType AND [EMP_COD] = wsEmpCod AND [DATE] = wsDate AND [LINE_NO] = wsLineno
The wsXXX declarations, you will have to replace them with direct values or have them DECLAREd earlier in your script.
If you ran this alone and recieved a value of 1 or more, then the data exists already in your table, at least those 5 first columns. A true duplicate test will require you to test EVERY column in your table, but it should give you an idea.
In the INSERT, to do it all as one statement, you can do this ...
INSERT INTO [Emp_table].[ACT].[LIST_EMP]
([ENTITY],[TYPE],[EMP_COD],[DATE],[LINE_NO],[ACT],[NAME])
VALUES
('REG','EMP','45233','2016-06-20 00:00:00:00','2','SKATING','JANE')
WHERE (SELECT COUNT(*) AS FoundRec FROM [Emp_table].[ACT].[LIST_EMP]
WHERE [ENTITY] = wsEntity AND [TYPE] = wsType AND
[EMP_COD] = wsEmpCod AND [DATE] = wsDate AND
[LINE_NO] = wsLineno) = 0
Just replace the wsXXX variables with the values you want to insert.
I hope that made sense.
I want to copy all columns from dbo.die to dbo.technology.
Both tables exist! In dbo.technology, the primary key is idTechnology
In dbo.die, the primary key is idDie and we have a foreign key, which is Technology_idTechnology in it, which connects the die table with the technology table.
How could I do that, so that the values got copied to the right rows, which match the same idTechnology?
I tried this:
INSERT INTO dbo.die
(Technology_idTechnology, Technology_D, Technology_Type, Technology_Manufacturer, Technology_SOI, Technology_Node, Technology_Name, Technology_Number_Metal, Technology_Number_Poly, Technology_Power_Cu, Technology_FEComplexity, Technology_FEComplexity_Sec, Technology_Trench, Technology_IMID, Technology_Remarks)
SELECT *
FROM dbo.technology tech
WHERE tech.idTechnology = idTechnology;
but I'm always getting an error!
Cannot insert duplicate key row in object 'dbo.die' with unique index 'ui_dieIdsample'. The duplicate key value is ().
Don't know what I should do.. I thought it's easy & simple
If a column is declared as NOT NULL (and has no default value), a value for the column must be specified in the INSERT statement.
In this specific case you should add Table2_Feld to the insert column list, and specify a value in the SELECT for it!
You will need to change your column list (lets say that its acceptable to insert a default value of 0 into column Table2_Feld)
INSERT INTO dbo.table2
(Table1_idTech, Tech_D, Techn_Type, Tech_Man,
Techn_Node, Tech_Name, Technology_Numb, Tech_Po,
Tech_FEC, Techn_Comp_Sec,
Tech_R,Table2_Feld)
select *,0 from table1 tech
In a database application, I want to insert, update and delete records in a table of database.
Table is as below:
In this table, Ga1_ID is Primary Key.
Suppose, I insert 5 records as show currently.
In second attempt, if I want to insert 5 other records and if any of these new records contains a primary key attribute which is already present in table it show error. Its fine.
But, when I insert new 5 records... how I can verify these new records's primary key value is not present. I mean, how to match or calculate the already present primary key attributes and then insert new records.
What is the best approach to manage this sort of situation ?
use following query in dataadapter:
da=new SqlDataAdapter("select Ga1_ID from table where Ga1_ID=#pkVal",conn);
DataSet=new DataSet();
da.fill(ds);
//pass parameter for #pkVal
da.SelectCommand.Parameters(1).Value = pkValue;
if(ds.Tables[0].Rows.Count>0) //If number of rows >0 then record exists
BEGIN
messagebox.show("Primary key present");
END
Hope its helpful.
Do not check existing records in advance, i.e. do not SELECT and then INSERT. A better (and pretty common) approach is to try to INSERT and handle exceptions, in particular, catch a primary key violation if any and handle it.
Do the insert in a try/catch block, with different handling in case of a primary key violation exception and other sql exception types.
If there was no exception, then job's done, record was inserted.
If you caught a primary key violation exception, then handle it appropriately (your post does not specify what you want to do in this case, and it's completely up to you)
If you want to perform 5 inserts at once and want to make sure they all succeed or else roll back if any of them failed, then do the inserts within a transaction.
you can do a lookup first before inserting.
IF EXISTS (SELECT * FROM tableName WHERE GA1_id=#newId)
BEGIN
UPDATE tableName SET Ga1_docid = #newdocID, GA1_fieldNAme = #newName, Ga1_fieldValue = #newVal where GA1_id=#newId
END
ELSE
BEGIN
INSERT INTO tableName(GA1_ID, Ga1_docid, GA1_fieldNAme Ga1_fieldValue) VALUES (value1,val2,value3,value4)
END
If you're using SQL Server 2012, use a sequence object - CREATE SEQUENCE.
This way you can get the next value using NEXT VALUE FOR.
With an older SQL Server version, you need to create the primary key field as an IDENTITY field and use the SCOPE_IDENTITY function to get the last identity value and then increment it manually.
Normally, you would like to have a surrogate key wich is generally an identity column that will automatically increment when you are inserting rows so that you don't have to care about knowing which id already exists.
However, if you have to manually insert the id there's a few alternatives for that and knowing wich SQL database you are using would help, but in most SQL implementations, you should be able to do something like:
IF NOT EXISTS
IF NOT EXISTS(
SELECT 1
FROM your_table
WHERE Ga1_ID = 1
)
INSERT INTO ...
SELECT WHERE NOT EXISTS
INSERT INTO your_table (col_1, col_2)
SELECT col_1, col_2
FROM (
SELECT 1 AS col_1, 2 AS col_2
UNION ALL
SELECT 3, 4
) q
WHERE NOT EXISTS (
SELECT 1
FROM your_table
WHERE col_1 = q.col_1
)
For MS SQL Server, you can also look at the MERGE statement and for MySQL, you can use the INSERT IGNORE statement.
I'm getting an error running the following Transact-SQL command:
CREATE UNIQUE NONCLUSTERED INDEX IX_TopicShortName
ON DimMeasureTopic(TopicShortName)
The error is:
Msg 1505, Level 16, State 1, Line 1
The CREATE UNIQUE INDEX statement
terminated because a duplicate key was
found for the object name
'dbo.DimMeasureTopic' and the index
name 'IX_TopicShortName'. The
duplicate key value is ().
When I run SELECT * FROM sys.indexes WHERE name = 'IX_TopicShortName' or SELECT * FROM sys.indexes WHERE object_id = OBJECT_ID(N'[dbo].[DimMeasureTopic]') the IX_TopicShortName index does not display. So there doesn't appear to be a duplicate.
I have the same schema in another database and can create the index without issues there. Any ideas why it won't create here?
It's not that the index already exists, but that there are duplicate values of the TopicShortName field in the table itself. According to the error message the duplicate value is an empty string (it might just be a facet of posting I guess). Such duplicates prevent the creation of a UNIQUE index.
You could run a query to confirm that you have a duplicate:
SELECT
TopicShortName,
COUNT(*)
FROM
DimMeasureTopic
GROUP BY
TopicShortName
HAVING
COUNT(*) > 1
Presumably in the other database the data are different, and the duplicates are not present.
The duplicate is in your data, try running this query to find it.
SELECT TopicShortName, COUNT(*)
FROM DimMeasureTopic
GROUP BY TopicShortName
HAVING COUNT(*) > 1
It's because you have records in the table already that are not unique (by the sounds of it, 2 records with a blank value in the TopicShortName field).
So, it's to do with the data, not the index itself.
If you are using code-based migrations, and you rename a property of an entity and you are having an unique index for the property, entity framework will create a new column and trying to add an unique index for the new column but the new column has all null values, therefore it will fail. You need to manually modify the migration code to copy the data from old column before the line to create index.
It should have specified the duplicate key value in the error message. "The duplicate key value is (' ', ' ', ' ') The statement has been terminated. You have duplicate values that need to be addressed.