I have a temporary table in a PostgreSQL function and I want to insert a new VARCHAR column. It should have a value that depends on another column of the table, named "amount".
When the amount is positive I would like the value of the column row to be credit and when the value is negative the column should be debit.
I have one more request: I want to round the value of amount column in 2 decimal digits
You want ALTER TABLE ... ADD COLUMN followed by an UPDATE.
I initially said ALTER TABLE ... ADD COLUMN ... USING but that was wrong on two counts. ADD COLUMN takes a DEFAULT not USING - and You can't do it in one pass because neither a DEFAULT expression nor a USING expression may not refer to other columns.
So you must do:
ALTER TABLE tablename ADD COLUMN colname varchar;
UPDATE tablename SET colname = ( CASE WHEN othercol < 0 THEN 'Credit' ELSE 'Debit' END );
Think carefully about whether zero should be 'Debit' or 'Credit' and adjust the CASE accordingly.
For rounding, use round(amount,2). There isn't enough detail in your question for me to be sure how; probably by UPDATEing the temp table with UPDATE thetable SET amount = round(amount,2) but without the context it's hard to know if that's right. That statement irreversibly throws information away so it should only be used on a copy of the data.
Related
I can add a column this way:
ALTER TABLE MyTable
ADD MyColumn BIT NOT NULL
CONSTRAINT MyConstraint
DEFAULT 0
Now, instead of the constant 0 I want to put a different value depending on my other columns in the MyTable. I.e. it is a one time computation during the column addition. How could I do that?
Also, I do not want my column to have a default value.
E.g. I have another BIT column called MyOldColumn and I want to just copy its value into the MyColumn.
Looks like you just want to add the column, then run an update using some calculation.
ALTER TABLE MyTable ADD MyColumn BIT;
UPDATE MyTable
SET MyColumn = SomeCalculation;
ALTER TABLE MyTable ALTER COLUMN MyColumn BIT NOT NULL;
Why set the column to null first then not null? Because it will be more performant. Setting it to null first means it's a meta-data only operation, and will not change the data pages. The final ALTER will also not change any pages (although it will read them all), because none of them are null.
Whereas if you set it to not null first then all pages get changed, and then changed again.
I created a new column [LastLoginDate-NoTime] with the data type Date. I already have another column [LastLoginDate] that is of Datetime datatype.
Columns with the values
I am trying to copy values from the LastLoginDate column to the LastLoginDate-NoTime column using this query:
UPDATE [dbo].[SapUsersExt]
SET [LastLoginDate] = [LastLoginDate-NoTime]
But the problem I am having is that when I execute this query, it sets the data to null in the original column.
Screenshot: Error
I am also trying to convert the data from the LastLoginDate to just date format in the new column LastLoginDate-NoTime so that I can use it in my application. How would I do that?
I am trying to copy values from the LastLoginDate column to the LastLoginDate-NoTime column using this query
In that case, you're doing it exactly backwards - you should use this SQL instead:
UPDATE [dbo].[SapUsersExt]
SET [LastLoginDate-NoTime] = [LastLoginDate]
The first column - right after the SET - is the target column into which your values will be written.
The second column, after the = symbol, is where the data comes from (column or expression).
You had it backwards - setting the column with the actual values, to all NULL ....
This of course only works for a "one time" update - this will not keep your columns in sync over time, when new data is being inserted. For such a case, you'd need a computed column
ALTER TABLE dbo.SapUsersExt
ADD LastLoginDateOnly AS CAST(LastLoginDate AS DATE) PERSISTED;
or a trigger.
Or maybe, you don't even really need to actually store that date-only value - just use
SELECT
CAST(LastLoginDate AS DATE),
.......
if you need to date-only value from LastLoginDate
I am creating a new database that requires a calculated column that pulls a percentage from one column (GrossMarginPercentage) and multiplies it by either an estimated value or an actual value column. Only one will contain a value and the other will be null.
Would any functions help me tell the new computed column what column (estimated or actual) to pull from and multiply by GrossMarginPercentage?
I tried:
Alter Table ChurnInfo
add DecMargin as case (when DecEstimated = 'Null' then
DecActual * GrossMarginPercentage else DecEst*GrossMarginPercentage end )
Solution: https://stackoverflow.com/a/56657223/11073192
I think you just want coalesce():
Alter Table ChurnInfo
add DecMargin as (coalesce(DecActual, DecEst) * GrossMarginPercentage);
I have one requirement. I already have a table named WorkOrder. In this table there is a column Named WorkorderId set as primary key and identity. The next one is voucherNumber. Now I want to generate voucherNumber automatically. The condition is voucher number will not repeat. E.g., first I insert 2 rows into the table and after that I delete the 2nd entry. The next time my voucher number should be 3. Again i insert 3 more entries then after that my voucher no should be 6. Then i delete one row from this table after that my voucher number should be 7. If i delete the last row (I mean 7) then next time the voucher number should the same.
Use IDENTITY(...) when creating the column. This will make a field auto-increment its value.
You'll have to drop the column first in case that it already exists. There is no (clean) way to make this happen on already existing columns.
For further information and examples you can check out http://www.w3schools.com/sql/sql_autoincrement.asp
Edit: Sorry, I have overlooked the info that you are already using IDENTITY(...) on the PK column. Unfortunately SQL-Server can only have a single column with the IDENTITY property per table... So in this case you'll have to make use of a trigger.
This is an example:
CREATE TRIGGER CountRows
ON TestCount
AFTER UPDATE
AS
UPDATE TestCount SET Cnt = Cnt +1 WHERE ID IN (SELECT ID from inserted)
GO
In case you want to enter an IDENTIFIER to the record, it is best to use uniqueIdentifier type column. It is a string constant in the form xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx, in which each x is a hexadecimal digit in the range 0-9 or a-f. For example, 6F9619FF-8B86-D011-B42D-00C04FC964FF is a valid uniqueidentifier value.
On insertion, you can simply proceed as follows;
Insert into MyTable
(WorkorderId, WorkName) values (NewId(), 'Test')
Using this, you can be sure the Id is globally unique.
I'm working with SQL Server 2008. Is it possible to alter a computed column without actually dropping the column and then adding it again (which I can get to work)? For example, I have this table:
CREATE TABLE [dbo].[Prices](
[Price] [numeric](8,3) NOT NULL,
[AdjPrice] AS [Price] / [AdjFactor],
[AdjFactor] [numeric](8,3) NOT NULL)
Later realizing that I have a potential divide by zero error I want to alter the [Adjprice] column to handle this, but if I just drop the column and add it again, I lose the column order.
I want to do something like:
ALTER TABLE dbo.[Prices]
ALTER COLUMN [AdjPrice] AS (CASE WHEN [AdjFactor] = 0 THEN 0 ELSE [Price] / [AdjFactor] END)
But this isn't correct. If this is possible, or there is another solution, I would appreciate the help.
Unfortunately, you cannot do this without dropping the column first.
From MSDN:
ALTER COLUMN
Specifies that the named column is to be changed or altered. ALTER COLUMN is not allowed if the compatibility level is 65 or lower. For more information, see sp_dbcmptlevel (Transact-SQL).
The modified column cannot be any one of the following:
A computed column or used in a computed column.
if you must maintain order, copy the data into a duplicate table, then rebuild the table to keep your column order, then copy the data from the duplicate table back in.
Just be sure to do this when there is no activity going on.
NO
if it is computed, what is the big deal dropping it and adding it again? is it PERSISTED and there are million of rows?
I do not think you can alter this column with out dropping.
So drop the colum then add new column.
If you find out any other way to do this please tell me.
its easy to overcome divide by zero error
use
SELECT
( 100 / NULLIF( 0, 0 ) ) AS value
it will return a null, if 0 is in that column,
instead of alter go for update by using the above example
Also read the 3rd normalization for computed column