I have a column which has a datatype : datetime. But now i want to convert it to datatype varchar. Can i alter the datatype without droppping the column? If yes, then please explain how?
MSDN says
ALTER TABLE mytable ALTER COLUMN mycolumn newtype
Beware of the limitations of the ALTER COLUMN clause listed in the article
If ALTER COLUMN doesn't work.
It is not unusual for alter column to fail because it cannot make the transformation you desire. In this case, the solution is to create a dummy table TableName_tmp, copy the data over with your specialized transformation in the bulk Insert command, drop the original table, and rename the tmp table to the original table's name. You'll have to drop and recreate the Foreign key constraints and, for performance, you'll probably want to create keys after filling the tmp table.
Sound like a lot of work? Actually, it isn't.
If you are using SQL Server, you can make the SQL Server Management Studio do the work for you!
Bring up your table structure (right-click on the table column and select "Modify")
Make all of your changes (if the column transformation is illegal, just add your new column - you'll patch it up in a moment).
Right-click on the background of the Modify window and select "Generate Change Script." In the window that appears, you can copy the change script to the clipboard.
Cancel the Modify (you'll want to test your script, after all) and then paste the script into a new query window.
Modify as necessary (e.g. add your transformation while removing the field from the tmp table declaration) and you now have the script necessary to make your transformation.
ALTER TABLE [table name] MODIFY COLUMN [column name] datatype
ALTER TABLE YourTableNameHere ALTER COLUMN YourColumnNameHere VARCHAR(20)
Type the below query:
alter table table_Name alter column column_name datatype
e.g.
alter table Message alter column message nvarchar(1024);
ALTER TABLE YourTableNameHere ALTER COLUMN YourColumnNameHere VARCHAR(20)
With SQL server 2008 and more, using this query:
ALTER TABLE [RecipeInventorys] ALTER COLUMN [RecipeName] varchar(550)
This work for postgresql 9.0.3
alter table [table name] ALTER COLUMN [column name] TYPE [character varying];
http://www.postgresql.org/docs/8.0/static/sql-altertable.html
ALTER TABLE [table_name] ALTER COLUMN [column_name] varchar(150)
ALTER TABLE YourTableNameHere ALTER COLUMN YourColumnNameHere VARCHAR(20) this is perfect for change to datatype
ORACLE - Alter table table_name modify(column_name new_DataType);
ALTER TABLE yourtable MODIFY COLUMN yourcolumn datatype
ALTER TABLE table_name
MODIFY (column_name data_type);
ALTER tablename MODIFY columnName newColumnType
I'm not sure how it will handle the change from datetime to varchar though, so you may need to rename the column, add a new one with the old name and the correct data type (varchar) and then write an update query to populate the new column from the old.
http://www.1keydata.com/sql/sql-alter-table.html
alter table [table name] remove [present column name] to [new column name.
Related
I tried below in sql server management, in a single query.
alter table add column amount2
update table set amount2=amount
I am getting column amount2 not found.
Can anyone tell me why this error?
That is not valid syntax (misses table name and column datatype) but in management studio use the batch separator GO between adding a column to an existing table and statements referencing the new column anyway.
Or alternatively you can use EXEC to execute it in a child batch.
SQL Server tries to compile all statements in the batch before execution and this will fail when it encounters the statement using this column.
There's a couple things wrong here.
The correct syntax for adding a column is MSDN - ALTER TABLE
ALTER TABLE [TableName] ADD [ColumnNAME] [DataType]
'Table' is a Reserved Keyword in SQL Server, although it is possible to have a table named 'Table'. You need to include brackets when referencing it.
SELECT * FROM [Table]
All together, you need
ALTER TABLE [Table] ADD [Amount2] INT
GO -- See Martin's answer for reason why 'GO' is needed here
UPDATE [Table] SET [Amount2] = [Amount]
You can get around this problem like this:
-- Alter the table and add new column "NewColumn"
ALTER TABLE [MyTable] ADD [NewColumn] CHAR(1) NULL;
-- Set the value of NewColumn
EXEC ('UPDATE [MyTable] SET [NewColumn] = ''A'' ');
There is a table full which contains data. Is it possible to change field from [not null] to [null] without dropping and recreating it?
SQL writes that table have to be dropped and recreated. :)
You can try:
alter table YourTable alter column YourColumn int null
Per Martin Smiths comment, a change in nullability does not require a copy of the table. On disk, each row has a nullabiltiy bitmap at the start. I thought the bitmap had to be resized in some cases, but apparently it contains a bit for each column, nullable or not nullable.
Have you tried to use ALTER TABLE XXX ALTER COLUMN YYY YOURTYPE NULL command?
This might help:
ALTER TABLE [Table] ALTER COLUMN [Column] [YourDataType] NULL
I have a table in MSSQL server 2008. I would like to change one of the column in that table to computed column. Could somebody tell me how do I do that ?
Preserve the old data:
EXEC sp_rename 'MyTable.OldCol', 'RenamedOldCol', 'COLUMN';
Add computed column
ALTER TABLE MyTable ADD ComputedCol AS (some expression);
Then, when you're happy
ALTER TABLE MyTable DROP COLUMN RenamedOldCol;
How to remove a column from an existing table?
I have a table MEN with Fname and Lname
I need to remove the Lname
How to do it?
ALTER TABLE MEN DROP COLUMN Lname
Generic:
ALTER TABLE table_name DROP COLUMN column_name;
In your case:
ALTER TABLE MEN DROP COLUMN Lname;
Your example is simple and doesn’t require any additional table changes but generally speaking this is not so trivial.
If this column is referenced by other tables then you need to figure out what to do with other tables/columns. One option is to remove foreign keys and keep referenced data in other tables.
Another option is to find all referencing columns and remove them as well if they are not needed any longer.
In such cases the real challenge is finding all foreign keys. You can do this by querying system tables or using third party tools such as ApexSQL Search (free) or Red Gate Dependency tracker (premium but more features). There a whole thread on foreign keys here
This is the correct answer:
ALTER TABLE MEN DROP COLUMN Lname
But... if a CONSTRAINT exists on the COLUMN, then you must DROP the CONSTRAINT first, then you will be able to DROP the COLUMN. In order to drop a CONSTRAINT, run:
ALTER TABLE MEN DROP CONSTRAINT {constraint_name_on_column_Lname}
In SQL Server 2016 you can use new DIE statements.
ALTER TABLE Table_name DROP COLUMN IF EXISTS Column_name
The above query is re-runnable it drops the column only if it exists in the table else it will not throw error.
Instead of using big IF wrappers to check the existence of column before dropping it you can just run the above DDL statement
The question is, can you only delete a column from an unexisting table ;-)
BEGIN TRANSACTION
IF exists (SELECT * FROM sys.columns c
INNER JOIN sys.objects t ON (c.[object_id] = t.[object_id])
WHERE t.[object_id] = OBJECT_ID(N'[dbo].[MyTable]')
AND c.[name] = 'ColumnName')
BEGIN TRY
ALTER TABLE [dbo].[MyTable] DROP COLUMN ColumnName
END TRY
BEGIN CATCH
print 'FAILED!'
END CATCH
ELSE
BEGIN
SELECT ERROR_NUMBER() AS ErrorNumber;
print 'NO TABLE OR COLUMN FOUND !'
END
COMMIT
The simple answer to this is to use this:
ALTER TABLE MEN DROP COLUMN Lname;
More than one column can be specified like this:
ALTER TABLE MEN DROP COLUMN Lname, secondcol, thirdcol;
From SQL Server 2016 it is also possible to only drop the column only if it exists. This stops you getting an error when the column doesn't exist which is something you probably don't care about.
ALTER TABLE MEN DROP COLUMN IF EXISTS Lname;
There are some prerequisites to dropping columns. The columns dropped can't be:
Used by an Index
Used by CHECK, FOREIGN KEY, UNIQUE, or PRIMARY KEY constraints
Associated with a DEFAULT
Bound to a rule
If any of the above are true you need to drop those associations first.
Also, it should be noted, that dropping a column does not reclaim the space from the hard disk until the table's clustered index is rebuilt. As such it is often a good idea to follow the above with a table rebuild command like this:
ALTER TABLE MEN REBUILD;
Finally as some have said this can be slow and will probably lock the table for the duration. It is possible to create a new table with the desired structure and then rename like this:
SELECT
Fname
-- Note LName the column not wanted is not selected
INTO
new_MEN
FROM
MEN;
EXEC sp_rename 'MEN', 'old_MEN';
EXEC sp_rename 'new_MEN', 'MEN';
DROP TABLE old_MEN;
But be warned there is a window for data loss of inserted rows here between the first select and the last rename command.
To add columns in existing table:
ALTER TABLE table_name
ADD
column_name DATATYPE NULL
To delete columns in existing table:
ALTER TABLE table_name
DROP COLUMN column_name
This can also be done through the SSMS GUI. The nice thing about this method is it warns you if there are any relationships on that column and can also automatically delete those as well.
Put table in Design view (right click on table) like so:
Right click on column in table's Design view and click "Delete
Column"
As I stated before, if there are any relationships that would also need to be deleted, it will ask you at this point if you would like to delete those as well. You will likely need to do so to delete the column.
If you are using C# and the Identity column is int, create a new instance of int without providing any value to it.It worked for me.
[identity_column] = new int()
Syntax:
ALTER TABLE TABLE_NAME DROP COLUMN COLUMN_NAME;
For Example:
alter table Employee drop column address;
I have SQL Server database and I just realized that I can change the type of one of the columns from int to bool.
How can I do that without losing the data that is already entered into that table?
You can easily do this using the following command. Any value of 0 will be turned into a 0 (BIT = false), anything else will be turned into 1 (BIT = true).
ALTER TABLE dbo.YourTable
ALTER COLUMN YourColumnName BIT
The other option would be to create a new column of type BIT, fill it from the old column, and once you're done, drop the old column and rename the new one to the old name. That way, if something during the conversion goes wrong, you can always go back since you still have all the data..
ALTER TABLE tablename
ALTER COLUMN columnname columndatatype(size)
Note: if there is a size of columns, just write the size also.
If it is a valid change.
you can change the property.
Tools --> Options --> Designers --> Table and Database designers --> Uncheck --> Prevent saving changes that required table re-creation.
Now you can easily change the column name without recreating the table or losing u r records.
if you use T-SQL(MSSQL); you should try this script:
ALTER TABLE [Employee] ALTER COLUMN [Salary] NUMERIC(22,5)
if you use MySQL; you should try this script:
ALTER TABLE [Employee] MODIFY COLUMN [Salary] NUMERIC(22,5)
if you use Oracle; you should try this script:
ALTER TABLE [Employee] MODIFY [Salary] NUMERIC(22,5)
Why do you think you will lose data? Simply go into Management Studio and change the data type. If the existing value can be converted to bool (bit), it will do that. In other words, if "1" maps to true and "0" maps to false in your original field, you'll be fine.
Go to Tool-Option-designers-Table and Database designers and Uncheck Prevent saving option
for me , in sql server 2016, I do it like this
*To rename column Column1 to column2
EXEC sp_rename 'dbo.T_Table1.Column1', 'Column2', 'COLUMN'
*To modify column Type from string to int:( Please be sure that data are in the correct format)
ALTER TABLE dbo.T_Table1 ALTER COLUMN Column2 int;
Alter column data type with check type of column :
IF EXISTS(
SELECT 1
FROM sys.columns
WHERE NAME = 'YourColumnName'
AND [object_id] = OBJECT_ID('dbo.YourTable')
AND TYPE_NAME(system_type_id) = 'int'
)
ALTER TABLE dbo.YourTable ALTER COLUMN YourColumnName BIT
In compact edition will take size automatically for datetime data type i.e. (8) so no need to set size of field and generate error for this operation...
I can modify the table field's datatype, with these following query: and also in the Oracle DB,
ALTER TABLE table_name
MODIFY column_name datatype;
Replace datatype without losing data
alter table tablename modify columnn newdatatype(size);