I keep getting this error message when trying to change the data type of my column:
alter table x modify column order_date date NOT NULL;
ERROR at line 1
ORA-00905 missing keyword
I not sure where I am going wrong, as I am aware there are many types of dates in sql?
Many thanks
The MODIFY clause does not take COLUMN as a keyword. This will work:
alter table x modify order_date date NOT NULL;
The syntax is documented in the Oracle SQL reference. Find out more.
We only need to include COLUMN with commands which have several different possibilities. For instance, with the ALTER TABLE ... DROP command, because we can drop columns, constraints or partitions....
alter table x drop column order_date ;
"when I tried entering NOT NULL, it said the table needed to be empty"
You should be able to apply a NOT NULL constraint, providing all the rows in the table have a value in the order_date column. The error message you get is quite clear:
ORA-01758 table must be empty to add mandatory (NOT NULL) column
This means your column has some rows without values. So, you need to update the table and populate those rows with some value; what you will use as a default depends on your business rules.
Related
I'm trying to understand the relationship between two operations in SQL - ADD COLUMN and CAST().
I tried to create a new column containing the lengths of another column's values, while that other column is inconveniently of type INTEGER:
ALTER TABLE inventory
ADD inventory_id_len AS (CHAR_LENGTH(CAST(inventory_id AS VARCHAR)) FROM rental);
But it returns:
ERROR: syntax error at or near "AS"
LINE 4: ADD inventory_id_len AS (CHAR_LENGTH(CAST(inventory_id AS V...
Thanks.
In Postgres, you need to use the generated always ... stored syntax to add a computed column. For your use case, that would look like:
alter table inventory
add inventory_id_len int
generated always as (char_length(inventory_id::text)) stored
;
A subquery makes no sense in that context; the computed column takes the value of column inventory_id on the very same row.
If you want to add the length of the id as a generated column:
ALTER TABLE inventory
ADD inventory_id_len INT GENERATED ALWAYS AS (LEN(inventory_id::text) STORED;
Because Postgres does not (yet) support virtual generated columns, a view might be more in line with what you want:
create view v_inventory as
select i.*, len(inventory_id::text) as inventory_id_len
from inventory i;
I am using Code first approach. how can i fix this problem?
I am assuming "Modified" column is a date time field in the table which is mandatory column.
You can resolve this issue in two ways
You can pass the "Modified" column field each time you do a insert.
Alter the column to accept null values if that field is not mandatory. Following is
sql query you can run to change the column to accept null values.
ALTER TABLE myTable ALTER COLUMN myColumn {DataType} NULL
I am using a reporting database which consists of 20 tables on SQL Server. In marketing table I have a column report_date which is currently a varchar(255). It is basically a date formatted in a way 2017-12-12. I want to change the type of this column to a date. I’m running this script but getting errors. The script is down below:
USE [reporting].[dbo].[marketing]
GO
SELECT CONVERT(date, 'report_date');
These are the errors I’m getting.
Msg 911, Level 16, State 1, Line 1
Database 'dbo' does not exist. Make sure that the name is entered correctly.
Msg 241, Level 16, State 1, Line 3
Conversion failed when converting date and/or time from character string.
How should I adjust the script?
If you want to change the column's data type (and you should) then you need to use an alter table statement. Your first error message is because of the USE directive - it should be
USE [reporting]
GO
Your second error message is because 'report_date' is a string constant, not a column name.
The select statement should be
SELECT CAST(report_date as date) -- Don't use Convert without the style argument....
FROM [dbo].[marketing]
Note that if you have even a single value that can't be converted to date you will get the second error again.
Basically I would recommend first making sure that the select statement completes without any exceptions, and only then alter the table:
USE reporting
GO
ALTER TABLE [dbo].[marketing]
ALTER COLUMN report_date DATE
GO
TRY THIS:
SELECT CONVERT(DATE, report_date) --If only for comparison
ALTER TABLE marketing ALTER COLUMN report_date DATE --If want to change in the table
The proper way to do this is like;
ALTER TABLE reportin.dbo.marketing ALTER COLUMN 'report_date' date
And you can check this How do you change the datatype of a column in MS SQL?
"Convert" is used for conversion from one datatype to other in select queries, you need to use alter statement for altering database columns and also
USE [databasename] is enough, so rewriting your query here :
USE [reporting]
GO
ALTER TABLE marketing ALTER COLUMN ReportDate DATE
Slow, but safe way is to:
Create a new column (ALTER TABLE dbo.MyTable ADD MyNewColumn DATE NULL;)
Update the new column using the old one (UPDATE dbo.MyTable SET MyNewColumn = CONVERT(DATE, MyColumn);)
Drop the old column (ALTER TABLE dbo.MyTable DROP MyColumn;) - Alternatively, you can rename this column instead and keep it as is)
Rename the new column (EXEC sp_rename 'dbo.MyTable.MyNewColumn', 'MyColumn', 'COLUMN';)
You might have to drop indexes beforehand, but this method (and it's alterations) help to prevent data loss.
If you encounter an error during casting, you should eliminate those values from the update (by for example adding a WHERE clause) and investigate them manually.
If you are using SQL Server 2012 or newer, you can use TRY_CONVERT() to ignore the values which cannot be converted to DATE. In this case you will have NULL in your new column.
Before you do anything, make sure, that all applications and code which is working with this column can handle the changes.
Notes
You might want to rebuild the table/indexes after a change like this.
I want to add or update columns using alter table if i am adding a new column i want show error. I am using the code below
alter table Personal_Details alter columns DOB datetime
if i uncheck the NULL to not NULL then it will shows column does not allow nulls; update fails;
i want to insert the fields in between columns not at end.
Plese fix my bug,
Thanks in advance.
The position of the column in the table declaration has nothing to do with its being NULL or NOT NULL.
If you are adding a column (of any type) which you want to be NOT NULL, i.e. you want to prohibit NULL values in that column, and the table already contains some rows, you must also provide some default value. For example:
ALTER TABLE Personal_Details
ADD COLUMN DOB datetime NOT NULL DEFAULT (GETDATE())
Otherwise the engine will attempt to add that column with NULLs as its values, which will violate the NOT NULL property, and the change, therefore, will be reverted.
Basically, the same applies when you want to set an existing column's NOT NULL property on while the column already contains NULLs. But in this case you must explicitly eliminate the NULLs before the change by either replacing them with values or removing the respective rows.
Source:
ALTER TABLE (Transact-SQL). (The particular section related to your problem is just above this code snippet.)
1)For ur adding column with not null problem
Use
ALTER TABLE Personal_Details ADD COLUMN DOB datetime NULL
Update the DOB column with the required dates and make sure there is no null in the column
then alter the column using
ALTER TABLE Personal_Details ALTER COLUMN DOB datetime not NULL
2)For your column going to the end problem...
you should not be worried...the order in which the columns are arranged doesnt matter...unless u are using a pathetic way of accessing data by column order..in which case again..u should stop accessing it by column order...
If the column order really matters you can change it using design option in the sql management table(rightclick on table >design and drag the column to its required place.)
I have a table with a column which contains a 'valid until' Date and I want to make sure that this can only be set to null in a single row within the table. Is there an easy way to do this?
My table looks like this (postgres):
CREATE TABLE 123.myTable(
some_id integer NOT NULL,
valid_from timestamp without time zone NOT NULL DEFAULT now(),
valid_until timestamp without time zone,
someString character varying)
some_id and valid_from is my PK. I want nobody to enter a line with a null value in column valid_until if there is already a line with null for this PK.
Thank you
In PostgreSQL, you have two basic approaches.
Use 'infinity' instead of null. Then your unique constraint works as expected. Or if you cannot do that:
CREATE UNIQUE INDEX null_valid_from ON mytable(someid) where valid_until IS NULL
I have used both approaches. I find usually the first approach is cleaner and it allows you to use range types and exclude constraints in newer versions of PostgreSQL better (to ensure no two time ranges overlap based on a given given someid), bt the second approach often is useful where the first cannot be done.
Depending on the database, you can't have null in a primary key (I don't know about all databases, but in sql server you can't). The easiest way around this I can think of is to set the date time to the minimum value, and then add a unique constraint on it, or set it to be the primary key.
I suppose another way would be to set up a trigger to check the other values in the table to see if another entry is null, and if there is one, don't allow the insert.
As Kevin said in his answer, you can set up a database trigger to stop someone from inserting more than one row where the valid until date is NULL.
The SQL statement that checks for this condition is:
SELECT COUNT(*)
FROM TABLE
WHERE valid until IS NULL;
If the count is not equal to 1, then your table has a problem.
The process that adds a row to this table has to perform the following:
Find the row where the valid until value is NULL
Update the valid until value to the current date, or some other meaningful date
Insert the new row with the valid until value set to NULL
I'm assuming you are Storing Effective-dated-records and are also using a valid from date.
If so, You could use CRUD stored procedures to enforce this compliance. E.G the insert closes off any null valid dates before inserting a new record with a null valid date.
You probably need other stored procedure validation to avoid overlapping records and to allow deleting and editing records. It may be more efficient (in terms of where clauses / faster queries) to use a date far in the future rather than using null.
I know only Oracle in sufficient detail, but the same might work in other databases:
create another column which always contains a fixed value (say '0') include this column in your unique key.
Don't use NULL but a specific very high or low value. I many cases this is actually easier to use then a NULL value
Make a function based unique key on a function converting the date including the null value to some other value (e.g. a string representation for dates and 'x' for null)
make a materialized view which gets updated on every change on your main table and put a constraint on that view.
select count(*) cnt from table where valid_until is NULL
might work as the select statement. And a check constraint limiting the cnt value to the values 0 and 1
I would suggest inserting to that table through an SP and putting your constraint in there, as triggers are quite hidden and will likely be forgotten about. If that's not an option, the following trigger will work:
CREATE TABLE dbo.TESTTRIGGER
(
YourDate Date NULL
)
CREATE TRIGGER DupNullDates
ON dbo.TESTTRIGGER
FOR INSERT, UPDATE
AS
DECLARE #nullCount int
SELECT #nullCount = (SELECT COUNT(*) FROM TESTTRIGGER WHERE YourDate IS NULL)
IF(#NullCount > 1)
BEGIN
RAISERROR('Cannot have Multiple Nulls', 16, 1)
ROLLBACK TRAN
END
GO
Well if you use MS SQL you can just add a unique Index on that column. That will allow only one NULL. I guess that if you use other RDBMS, this will still function.