How can I delete the value of a field from a database, using query code? I only know where the field is located in the database. (ex: column['phone number']row[3])
It should be something like this "DELETE FROM ... WHERE ..."
There is nothing like delete the field in database i.e. if you want to remove the complete row then you can do that easily like this
DELETE FROM TABLE WHERE COLUMN1=#myValue
But if you wanted to remove one value of the row in that case you should update that value as NULL
UPDATE TABLE SET COLUMN1=NULL WHERE COLUMN1=#myValue
I have used where clause from my imagination. you can always use whatever you want.
The DELETE statement allows you to delete RECORDS.
When you want to set a field to an empty value, use the UPDATE statement.
See this for more info.
UPDATE [YOUR_TABLE] SET [YOUR_FIELD] = NULL WHERE [YOUR_PRIMARY_KEY] = VALUE
Yes first you need to use delete command. Then after this insert update command then only the records will be deleted from the database. I agree that you have deleted records but its not showing because you haven't updated it.
Related
I want to delete specific values/data from one column with the WHERE condition. Putting in another way, I don't want to delete the complete row. Is it possible?
You can re-set values using update:
update t
set col = NULL
where . . .;
Yes it is possible to delete the particular value/data from the column using WHERE condition. You can use the below code in SQL command to delete that particular column.
Update Table_Name set Column_Name=null where Column_Id=xxx
or you can even update that by changing the Column_name value to an empty string ' ' Like below
Update Table_Name set Column_Name='' where Column_Id=xxx
Recently I have started learning Oracle-sql. I know that with the help of DELETE command we can delete a particular row(s). So, Is it possible to delete entire data from a particular column in a table using only DELETE command. (I know that using UPDATE command by setting null values to entire column we can achieve the functionality of DELETE).
DELETE
The DELETE statement removes entire rows of data from a specified
table or view
If you want to "remove" data from particular column update it:
UPDATE table_name
SET your_column_name = NULL;
or if column is NOT NULL
UPDATE table_name
SET your_column_name = <value_indicating_removed_data>;
You can also remove entire column using DDL:
ALTER TABLE table_name DROP COLUMN column_name;
In SQL, delete deletes rows not columns.
You have three options in Oracle:
Set all the values to NULL using update.
Remove the column from the table.
Set the column to unused.
The last two use alter table:
alter table t drop column col;
alter table t set unused (col);
Use Invisible Type, which is from an oracle 12cR2.
ALTER TABLE LOG1
MODIFY operation INVISIBLE
It is a better than drop of a particular column.If you need to visible you can get back by altering with an VISIBLE of a column name.
update employee set commission=nvl2(commission,'','')
this will remove all the data from the column
UPDATE UPI_ATTRIBUTE SET SITE_INC ='0'
WHERE USER_PROFILING_NAME IN ('CAR_IMPLICIT','CAR_EXPLICIT')
Above is my query that I am using to update the columns in UPI_ATTRIBUTE table. And suppose if I need to rollback the above changes that I am doing with update query, then how can I use the delete query in the above case? Currently SITE_INC is empty. So after updating the table it will have 0 in that. And If I need to rollback the changes then I need to make it empty again.
How can I delete the value 0 from above column after updating.
You cannot "delete" data to rollback an update.
Even if the only change that you'll do is set a flag from "NULL" to "Y" and vice versa, you can't really determine which value to update when you do multiple updates.
update 1 : set from "NULL" to "0"
update 2 : set from "0" to "something else"
update 3 : Rollback changes (rollback to which state)?
If you want to really rollback changes to specific rows (instead of the complete table, which can be done using Flashback), you can audit the changes to "remember" the values and then revert back to them.
Even then, you should consider which point to revert to, when you have multiple updates.
Not sure Oracle have final table/old table function for select/update.
For DB2 for z/OS, it have such function:
SELECT LASTNAME, BONUS FROM FINAL TABLE
(UPDATE EMP SET BONUS = BONUS * 1.3
WHERE JOB = 'CLERK');
Then, the result set of the select include all the updated rows. you can use rownum or other unique value, then you can update it back to any value as you want.
One attribute in a table became corrupted after a certain point in a table of mine. I want to delete every pat_coun attribute if it has an ID that begins with 11 (number, not text). So I don't want to get rid of any of the records in the database, just clear out the attribute pat_coun if it's ID begins with 11
DELETE pat_coun from myTable
WHERE id %11
Just want to make sure this is right before I go deleting stuff. Thanks.
To clear out an attribute, do NOT use the DELETE function! That deletes a row from your table!
You need to use UPDATE instead:
UPDATE myTable
SET pat_coun = NULL
WHERE id LIKE '11%'
If you want to delete a record (a row) you can use
DELETE FROM myTable
WHERE condition
If you just want to "clear" a particular column you should use
UPDATE myTable
SET pat_coun = 0 // or NULL or whatever you please
WHERE condition
For condition IMHO you should convert your number to string and check like this
WHERE CONVERT(VARCHAR(20), pat_coun) LIKE '11%'
try this
update myTable
set pat_coun = null
where id like '11%'
If only one row with a distinct field is to be updated,I can use:
insert into tab(..) value(..) on duplicate key update ...
But now it's not the case,I need to update 4 rows inside the same table,which have its field "accountId" equal to $_SESSION['accountId'].
What I can get out of my mind at the moment is:
delete from tab where accountId = $_SESSION['accountId'],
then insert the new rows.
Which obviously is not the best solution.
Has someone a better idea about this?
Use the update just like that!
update tab set col1 = 'value' where accountId = $_SESSION['accountId']
Moreover, MySQL allows you to do an update with a join, if that makes your life a bit easier:
update
tab t
inner join accounts a on
t.accountid = a.accountid
set
t.col1 = 'value'
where
a.accountname = 'Tom'
Based on your question, it seems like you should review the Update Statement.
Insert is used to put new rows in - not update them. Delete is used to remove. And Update is used to modify existing rows. Using "Insert On Duplicate Key Update" is a hackish way to modify rows, and is poor form to use when you know the row is already there.
load all of the values in to a temporary table.
UPDATE all of the values using a JOIN.
INSERT all of the values from the temp table that don't exist in the target table.
You can use replace statement. This will work as a DELETE followed by INSERT