I have a table with more than 1.5 million records, in which I have two columns, A and B. Mistakenly the column values of A got inserted into the column B and column B's values got inserted to A.
Recently only we found the issue. What will be the best option to correct this issue? Rename the column names interchangingly (I don't know how it can be possible, since if we nename A to B, when B already exists), or swapping the values contained in the two columns?
Hi, You can have the below query to swap the columns,
UPDATE table_name SET A = B, B = A;
But you have huge amount of date in this case renaming will be good. But renaming of column name because of data issue is not a right solution. So you can have above update query to update your data.
Before updating take a backup of table which you are updating using the query,
CREATE TABLE table_name_bkp AS SELECT * FROM table_name;
Always have a backup while playing with original data which will not mess up
15 lakh rows aren't a big deal for SQL server. Switching column names have many cons in relational DB such as index, foreign Key and also you may have to do lots of impacts. So, I would like to suggest to go for traditional path. Simply do the update.
Related
Here is the scenario... I've two databases (A & B) with same schema but different records. I'd like to transfer B's data into corresponding tables in DB A.
Lets say we have tables named Question and Answer in both databases. DB A contains 10 records in Question table and 30 in Answer table. Both tables have identity column Id starting with 1(& auto increment), and there is 1 to many relation between Question and Answer.
In DB B, we have 5 entries in Question table and 20 in Answer.
My requirement is to copy data of both tables from source DB B into destination DB A without having any conflict in identity column while maintaining the relation between two tables during data transfer.
Any solution or potential workaround would be highly appreciated.
I will not write SQL here but here is what I think can be done. Make sure to use Identity insert ON and OFF.
Take maxids of both tables from DB A like A_maxidquestion and A_maxidanswer.
Select from B_question . In select column add derived col QuestionID+A_maxidquestion.This will be your new ID.
Select from B_Answer . In select column add derived col AnswerID+A_maxidanswer and fk id as QuestionID+A_maxidquestion.
Note- Make sure Destination table is not beeing used by any other process for inserting values while you are inserting
One of the best approaches to something like this is to use the OUTPUT clause. https://learn.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql?view=sql-server-2017 You can insert the new parent and capture the newly inserted identity value which you can use to insert the children.
You can do this set based if you also include a temp table which would hold the original identity value and the new identity value.
With no details of the tables that is the best I can do.
I have two tables A(i,j,k) and B(m,n).
I want to update the 'm' column of B table by taking sum(j) from table A. Is it possible to do it in Vertica?
Following code can be used for Teradata, but does Vertica have this kind of flexibility?
Update B from (select sum(j) as m from A)a1 set m=a1.m;
The Teradata SQL syntax won't work with Vertica, but the following query should do the same thing :
update B set m = (select sum(j) from A)
Depending on the size of your tables, this may not be an efficient way to update data. Vertical is a WORM (write once read many times) store, and is not optimized for updates or deletes.
An alternate way would be to first temporarily move the data in the target table to another intermediate (but not temporary) table. After that write a join query using the other table to produce the desired result, and finally use export table with that join query. Finally drop the intermediate table. Of course, this is assuming you have partitioned your table in a way suitable for your update logic.
I have been asked to look into a manual process that one of my colleagues is completing every now and again.
He sometimes needs to add a new column onto a large table (200 million rows), it is taking him more than 1 hour to do this. Before you ask, yes, the columns are nullable but sometimes the new column will have 90% data in it.
Instead of adding a new column to the existing table, he...
Creates a new table
Select (*) from old table (inserts into new)
Adds the new column as part of his script
Then he deletes the old table and renames the new table back to the original, adds index and then compresses. He says it much quicker like that.
If this is the best way then I will try and write SSIS package to try and make the process more seamless
Any advice is welcome!
Thanks
creating a new table structure and moving all the data to that table and delete the prior table is a good way just for a few data,you can do it by wizard in SQL Server. but it is the worst way for solving this problem(millions of data).
for large amount of data (millions of records) you should use "Alter Table".
Alter Table MyTable
ADD NewColumn nvarchar(10) null
the new column will add to the table as the last column.
if you use this script it takes less that one second because all data will not moving,you just add a new column in to the table.
but if you use the wizard method as you mentioned with millions of data records it takes hours.
as Ali says
alter Table MyTable
ADD NewColumn nvarchar(10) null
but then to fill in 90% of data. As he has a table already with it in and the key he's joining on in the copy so this is all he needs:
UPDATE MyTable
SET [NewColumn] = b.[NewColumn]
FROM MyTable a INNER JOIN NewColumnTable b ON a.[KeyField]= b.[KeyField]
would be a lot quicker. You could do it in SSIS but if this happens a lot then not really worth it for a few lines of SQL.
I have a table people with less than 100,000 records and I have taken a backup of this table using the following:
create table people_backup as select * from people
I add some new records to my people table over time, but eventually I want to merge the records from my backup table into people. Unfortunately I cannot simply DROP my table as my new records will be lost!
So I want to update the records in my people table using the records from people_backup, based on their primary key id and I have found 2 ways to do this:
MERGE the tables together
use some sort of fancy correlated update
Great! However, both of these methods use SET and make me specify what columns I want to update. Unfortunately I am lazy and the structure of people may change over time and while my CTAS statement doesn't need to be updated, my update/merge script will need changes, which feels like unnecessary work for me.
Is there a way merge entire rows without having to specify columns? I see here that not specifying columns during an INSERT will direct SQL to insert values by order, can the same methodology be applied here, is this safe?
NB: The structure of the table will not change between backups
Given that your table is small, you could simply
DELETE FROM table t
WHERE EXISTS( SELECT 1
FROM backup b
WHERE t.key = b.key );
INSERT INTO table
SELECT *
FROM backup;
That is slow and not particularly elegant (particularly if most of the data from the backup hasn't changed) but assuming the columns in the two tables match, it does allow you to not list out the columns. Personally, I'd much prefer writing out the column names (presumably those don't change all that often) so that I could do an update.
Is there any way to copy all column values from one table to another except the Identity column, without mentioning all the rest of the column names?
I have a table with 63 columns. I created a temporary table with -
SELECT * INTO #TmpWide FROM WideTable WHERE 1 = 0
Now I want to copy some data from WideTable to #TmpWide. I need all the columns of WideTable except the Identity Id column, because I want the copied data to have their own sequential Id's in #TmpWide from 1 to onward. Is it possible without mentioning the (63-1) column names?
You could try dropping the column after the table is created:
SELECT * INTO #TmpWide FROM WideTable WHERE 1=0
ALTER TABLE #TmpWide DROP COLUMN [Id]
This does feel a little ugly or hack-y, but it should do the trick.
There isn't a way to do that, but also it is a bad idea to use * in a situation like this. If WideTable changes you will be forced to change the stored procedures that SELECT * from it. I wrote hundreds of stored procs like this and all it did was create nightmares I'm still dealing with today. Good luck.