Code:
ALTER TABLE tblUser
DROP COLUMN Mobile
Error:
ALTER TABLE DROP COLUMN Mobile failed because one or more objects access this column.
This column had values in Table. How can I delete all objects that access this column?
How can I DROP COLUMN with values?
how can do it with code? How can I delete all constraints in column automatically?
ALTER TABLE DROP COLUMN Mobile failed because one or more objects access this column.
Your column won't be deleted. Because one column or multiple columns are getting reference from this column that you want to delete.
So first, you will have to find in which table your column is being referenced by below query.
SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE TABLE_NAME = 'TABLENAME'
It will show you all constraints of all tables of your current database. You need to find it and remove the constraint. After that your column will be deleted successfully because there is no reference of your column in any table.
To remove constraint from column - use below query
alter table tablename
drop constraint constraintid
SQL Search is a great tool. I will search for your all the objects which are using the targeted object.
You can easily find where your column is being used, then simply you can modify or drop that objects too.
Use below query to find the constraints name for particular tablename
SELECT * FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS WHERE TABLE_NAME = 'TABLENAME'
Noe you can see the constraints name under constraint_name column, drop all constraint using below syntax
ALTER TABLE TABLENAME DROP CONSTRAINT CONSTRATINTSNAME
After that you can use below statement to drop the column
ALTER TABLE TABLENAME DROP COLUMN COLUMNNAME
You need to know what those constraints are and what their names are in order to drop them; there's nothing in SQL Server to say DROP ALL CONSTRAINTS and just do it. – marc_s yesterday
Related
I want to alter a table in my Crate DB to change the primary key constraint to add a column to the existing one. If I need to drop the constraint and create a new one what would be the SQL syntax for the same. I have been trying the conventional SQL syntax and it does not seem to work:
alter table my_data_table drop primary key;
the above command gives an error:
SQLActionException[SQLParseException: line 1:34: no viable alternative at input 'alter table my_data_table drop']
I checked the Alter table SQL reference and can only find ways to add columns but nothing about altering the constraints.So if you are aware of how to do this, please let me know. cheers!
there's no way to alter the primary key once a table has been created. You need to create a new table that has the schema you'd like to have and then either move the data over with COPY TO and COPY FROM or with insert into to_table (i) (select ... from t). With CrateDB > 2.0 it's also possible to rename tables, so you can still use the original table name.
First use the following code snippets for finding the constraints
SELECT Col.Column_Name from
INFORMATION_SCHEMA.TABLE_CONSTRAINTS Tab,
INFORMATION_SCHEMA.CONSTRAINT_COLUMN_USAGE Col WHERE
Col.Constraint_Name = Tab.Constraint_Name
AND Col.Table_Name = Tab.Table_Name
AND Constraint_Type = 'PRIMARY KEY'
AND Col.Table_Name = '<your table name>'
Then use this to drop the constraint
ALTER TABLE Customer DROP CONSTRAINT Constraint_Name;
P.S: considering you are using SQL SERVER
When I add a column to my my table with alter table, it is inserted as the last record. Is there a way to insert the column into the position I choose?
Thank you.
Some dbms let you control the column position with an alter table statement, but most do not. MySQL is one that does. Assume you start with
create table table_name (b char(1), d char(1));
You can alter that table to put column a first, and alter it again to put c after b.
alter table table_name add column a char(1) first;
alter table table_name add column c char(1) after b;
All dbms support "reordering" columns using create view... and select... though.
In the relational model of data, the order of columns is irrelevant. But I know what it's like to work in companies where that irrelevance is irrelevant.
I have a FK inside my table but i want to modify the parent table for the FK . so is there an alter command that can achieve this ? or i need to remove the FK and create a new one ?
Thanks
Add this to your PK and it will automatically update all FKs for you:
ON UPDATE CASCADE
For full details, you can read this article.
EDIT Based on your comment, if you want to change the PK data type, it depends on the change:
If the old type can be implicitly casted to the new type without any loss:
Change the PK type first.
Change the FK type to the same.
If the old type cannot be implicitly casted to the new type without any loss:
Break the relationship first (i.e. remove the FK restriction/index).
Convert the PK. If the data needs to be modified, save both the old values and the new ones in a temporary table.
Convert the FK. If the PK data was changed in previous step, update the FK using the mapped values from the temporary table.
Create the relationship again (i.e. create the FK restriction/index).
To modify the data type, use the ALTER command, the syntax is:
ALTER TABLE table_name
ALTER COLUMN column_name datatype
Examples:
ALTER TABLE table_name
ALTER COLUMN id NUMBER(10,2);
ALTER TABLE table_name
ALTER COLUMN id VARCHAR(20);
For full details, you can read this article.
Looks like you are looking for alter statement but since you didn't mention exactly what you are looking to modify; I assume that you want to change column data type size. You can do something like this (an example; say you want to change size from 10 to 15)
alter table sample3
alter column name varchar(15)
EDIT:
In that case this is what you should be doing. You need to drop the existing constraint and recreate the constraint to point to TableC
alter table TableA
drop constraint your_FK_constraint_name
alter table TableA
add constraint constraint_name
FOREIGN KEY (column_name) references TableC(some other column name)
An Example:
alter table sample2
drop constraint FK__sample2__realnam__09DE7BCC
alter table sample2
add constraint FK__sample2__realnam
FOREIGN KEY (realname) references sample1(name)
Based on this comment, "now my current FK inside TableA is referring to another table primary key TableB. but i need my modify my current FK to refer to tableC instead of tableB ... this what i need (to modify the parent table for my FK)– "
The parent table is TableB. No action is required on that table.
On TableA, you have to:
Drop the existing foreign key constraint.
Update as necessary so that all values in the applicable column have a matching value in TableC.
Add a new foreign key constraint.
in that order.
Edit Starts Here
Here is a link to the syntax,
[Name] [major_version] [minor_version] [revision] [install_failures]
s 23 1 NULL 0
This is my table. How can I delete the revision column (not the value, the complete revision column) from table?
ALTER TABLE `table_name` DROP COLUMN `revision`;
You can do this with the following sql
ALTER TABLE table_name
DROP COLUMN revision
Here can you read simple documentation on that.
Use ALTER statement
ALTER TABLE table_name DROP COLUMN revision;
The ALTER TABLE statement is used to
add, delete, or modify columns in an
existing table.
Syntax :
ALTER TABLE table_name
DROP COLUMN column_name
You have to use the alter table statement to delete the revision column from your table.
The ALTER TABLE statement is used to
add, delete, or modify columns in an
existing table.
your delete column syntax will look like this
ALTER TABLE table_name
DROP COLUMN revision
This is very simple...use this
ALTER TABLE table_name DROP COLUMN column_name
Here are some links that will help you.
techonthenet, w3schools, php.about, sqlzoo.
I need to add a new column to a MS SQL 2005 database with an initial value. However, I do NOT want to automatically create a default constraint on this column. At the point in time that I add the column the default/initial value is correct, but this can change over time. So, future access to the table MUST specify a value instead of accepting a default.
The best I could come up with is:
ALTER TABLE tbl ADD col INTEGER NULL
UPDATE tbl SET col = 1
ALTER TABLE tbl ALTER COLUMN col INTEGER NOT NULL
This seems a bit inefficient for largish tables (100,000 to 1,000,000 records).
I have experimented with adding the column with a default and then deleting the default constraint. However, I don't know what the name of the default constraint is and would rather not access sysobjects and put in database specific knowledge.
Please, there must be a better way.
To add the column with a default and then delete the default, you can name the default:
ALTER TABLE tbl ADD col INTEGER NOT NULL CONSTRAINT tbl_temp_default DEFAULT 1
ALTER TABLE tbl drop constraint tbl_temp_default
This filled in the value 1, but leaves the table without a default. Using SQL Server 2008, I ran this and your code, of alter update alter and did not see any noticeable difference on a table of 100,000 small rows. SSMS would not show me the query plans for the alter table statements, so I was not able to compare the resources used between the two methods.
I'd ALTER TABLE tbl ADD col INTEGER CONSTRAINT tempname DEFAULT 1 first,, and drop the explicitly named constraint after (presumably within a transaction).
Another, maybe more native, way would be:
ALTER TABLE tbl ADD COLUMN col INTEGER NOT NULL DEFAULT 1;
ALTER TABLE tbl ALTER COLUMN col DROP DEFAULT;
I'm not sure how long this function exists, but the PostgreSQL documentation goes back to version 7.1 and for 7.1 it is already described.
You can do it in an insert trigger
If you add a default constraint when creating the table, you won't know what it is called. However, if you add a constraint with ALTER TABLE, you must name the constraint. In this case, you would be able to ALTER TABLE DROP CONSTRAINT (This applies to T-SQL, not sure about other databases.)
However, this would require you to CREATE TABLE with NULL column, ALTER TABLE to add the constraint, make the column NOT NULL, and finally DROP CONSTRAINT.
I don't believe an insert trigger would work as someone else mentioned, because your rows are already added.
I think the way you describe may, in fact, be the most efficient and elegant solution.