问题
I have a table that has several nullable integer columns. This is undesirable for several reasons, so I am looking to update all nulls to 0 and then set these columns to NOT NULL. Aside from changing nulls to 0, data must be preserved.
I am looking for the specific SQL syntax to alter a column (call it ColumnA) to \"not null\". Assume the data has been updated to not contain nulls.
Using SQL server 2000.
回答1:
First, make all current NULL values disappear:
UPDATE [Table] SET [Column]=0 WHERE [Column] IS NULL
Then, update the table definition to disallow NULLs:
ALTER TABLE [Table] ALTER COLUMN [Column] INTEGER NOT NULL
回答2:
I had the same problem, but the field used to default to null, and now I want to default it to 0. That required adding one more line after mdb's solution:
ALTER TABLE [Table] ADD CONSTRAINT [Constraint] DEFAULT 0 FOR [Column];
回答3:
You will have to do it in two steps:
- Update the table so that there are no nulls in the column.
UPDATE MyTable SET MyNullableColumn = 0
WHERE MyNullableColumn IS NULL
- Alter the table to change the property of the column
ALTER TABLE MyTable
ALTER COLUMN MyNullableColumn MyNullableColumnDatatype NOT NULL
回答4:
For Oracle 11g, I was able to change the column attribute as follows:
ALTER TABLE tablename MODIFY columnname datatype NOT NULL;
Otherwise abatichev's answer seemed good. You can't repeat the alter - it complains (at least in SQL Developer) that the column is already not null.
回答5:
this worked for me:
ALTER TABLE [Table]
Alter COLUMN [Column] VARCHAR(50) not null;
回答6:
As long as the column is not a unique identifier
UPDATE table set columnName = 0 where columnName is null
Then
Alter the table and set the field to non null and specify a default value of 0
回答7:
this seems simpler, but only works on Oracle:
ALTER TABLE [Table]
ALTER [Column] NUMBER DEFAULT 0 NOT NULL;
in addition, with this, you can also add columns, not just alter it. It updates to the default value (0) in this example, if the value was null.
回答8:
In my case I had difficulties with the posted answers. I ended up using the following:
ALTER TABLE table_name CHANGE COLUMN column_name column_name VARCHAR(200) NOT NULL DEFAULT '';
Change VARCHAR(200) to your datatype, and optionally change the default value.
If you don't have a default value you're going to have a problem making this change, as default would be null creating a conflict.
回答9:
In case of FOREIGN KEY CONSTRAINT... there will be a problem if '0' is not present in the column of Primary key table. The solution for that is...
STEP1:
Disable all the constraints using this code :
EXEC sp_msforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT all"
STEP2:
RUN UPDATE COMMAND (as mentioned in above comments)
RUN ALTER COMMAND (as mentioned in above comments)
STEP3:
Enable all the constraints using this code :
exec sp_msforeachtable @command1="print '?'", @command2="ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all"
回答10:
For the inbuilt javaDB included in the JDK (Oracle's supported distribution of the Apache Derby) the below worked for me
alter table [table name] alter column [column name] not null;
回答11:
Making column not null and adding default can also be done in the SSMS GUI.
- As others have already stated, you can't set "not null" until all the existing data is "not null" like so:
UPDATE myTable SET myColumn = 0
- Once that's done, with the table in design view (right click on table and click "design view"), you can just uncheck the Allow Nulls columns like so:
- Still in design view with the column selected, you can see the Column Properties in the window below and set the default to 0 in there as well like so:
回答12:
Let's take an example:
TABLE NAME=EMPLOYEE
And I want to change the column EMPLOYEE_NAME to NOT NULL. This query can be used for the task:
ALTER TABLE EMPLOYEE MODIFY EMPLOYEE.EMPLOYEE_NAME datatype NOT NULL;
回答13:
You can change the definition of existing DB column using following sql.
ALTER TABLE mytable modify mycolumn datatype NOT NULL;
来源：https://stackoverflow.com/questions/689746/altering-a-column-null-to-not-null