I'm swapping column values in a table using the following statement:
UPDATE SwapTable
SET ValueA=ValueB
,ValueB=ValueA
This works and the values do get swapped, as can be verified by this SQL Fiddle.
However, if we did such thing in (mostly any) other language, we would end up with both ValueA and ValueB having identical values.
So my question is why/how this works in SQL.
You can just see the execution plan.
Select all the rows from the table and make it as a row set.
Open a transaction
Update the table referenced (SwapTable) with corresponding row address, from the old values read from the row set to the field reference.
Commit -- done updating.
Related
When insert I need edit a value if it is null. I create a trigger but I don't know how to edit inserted table.
ALTER TRIGGER [trigger1] on [dbo].[table]
instead of insert
as
declare #secuencia bigint, #ID_PERSONA VARCHAR;
select #secuencia = SECUENCIA from inserted
select #ID_PERSONA = ID_PERSONA from inserted
if #secuencia is null begin
set inserted.SECUENCIA = NEXT VALUE FOR SEQ_BIOINTEG --(Sequence)
end
i dont know how to edit inserted table.
You do not. That table is read only.
Note how your trigger also says:
instead of insert
There is no way to edit the inserted table.
What you do instead, is setting up an INSERT command for the original table, using the data from the inserted table to filter to the ROWS of inserted - mostly by a join.
Changing inserted makes no sense, logically - because triggers in SQL are one of two things:
INSTEAD OF - then there is no actual insert happening for inserted to start with. Instead of doing the insert, the trigger is called. As such, changing inserted - makes no sense.
AFTER - then the insert already happened (and you UPDATE the rows). As the trigger runs after the update, changing inserting makes no sense.
Note that I say ROWS - your trigger has one very basic error: it assumes inerted contains ONE row. It is a table - it is possible the changes come from an insert statement that inserts multiple rows (which is trivial, i.e. select into, or simply an insert with values for multiple rows). Handle those.
select #ID_PERSONA = ID_PERSONA from inserted
Makes NO sense - inserted is a table, so ID_PERSONA from inserted contains what value, if 2 rows are inserted? You must treat inserted like any other table.
Apart from all the varied issues with your trigger code, as mentioned by others, the easiest way to use a SEQUENCE value in a table is to just put it in a DEFAULT constraint:
ALTER TABLE dbo.[table]
ADD CONSTRAINT DF_table_seq
DEFAULT (NEXT VALUE FOR dbo.SEQ_BIOINTEG)
FOR SECUENCIA;
I have a database table with about 100 columns (bulky, I know). I have about half of these columns which I will need to update iteratively to set Is Null or "" values to "TBD".
I compiled all 50 some columns which need to be updated into an update query with Access SQL code that looked something like this...
UPDATE tablename
SET tablename.column1="TBD", tablename.column2="TBD", tablename.column3="TBD"....
WHERE tablename.column1 Is Null OR tablename.column1="" OR tablename.column2 Is Null OR tablename.column2="" OR tablename.column3 Is Null OR tablename.column3=""....
Two issues: This query with 50 columns receives a "query is too complex" error.
This query is also just functionally wrong...because I'm losing data within these columns due to the WHERE statement. Records that had values populated which I did not want to update are being updated because of the OR clause.
My question is how can I go about updating all of these columns and setting their null or empty values to a particular value (in this case, "TBD")?
I know that I can just use a select query to select the columns I need to update, run it, and just CTRL+H to find & replace "" to "TBD". However, I'm worried about the potential for this to introduce errors into my dataset. I also know I could also go through column by column and update these values via an update query. However, this would be quite time consuming with 50+ columns & the iterative updates which I need to run on the entire dataset.
I'm leaning towards this latter route. I am still wondering if there are any other scripted options which I can build into a query to overcome such an issue, and that leads me here to you.
Thank you!
You could just run 50 queries:
UPDATE table SET column1="TBD" WHERE column1 IS NULL OR column1 = "";
An optimization could be:
Create a temporary table which determines which rows actually would need an update: Concatenate all column values such that a single NULL or empty would result in an record in your temp table. This way you only have to scan the base table once.
Use the keys from that table to focus on those rows only.
Etc.
That is safe and only updates your empty values (where as your previous query would have updated all columns unless you would have checked every value first with an IFNULL).
This query style also does not run into the too complex issue
You could issue one query as:
UPDATE tablename
SET column1 = iif(column1 is null or column1 = "", "TBD", column1),
column2 = iif(column2 is null or column2 = "", "TBD", column2),
. . .;
If you don't mind potentially updating all rows, you can leave out the where clause.
I have never really worked with Triggers before in MSSQL but I think it'll be what I need for this task.
The structure of the table is as such:
ID|****|****|****|****|****|****|****|TOUROPERATOR
The Tour Operator Code is the code that tells us what company owned the flight we carried out for them. Two of those codes (there are 24 in total) are outdated. Our users requested that those two be changed but the tour operator code is pulled from a database we don't control. The FlightData table however, we do control. So I was thinking a trigger could change the tour operator code if it was one of the two outdated ones, to the correct ones instead respectively when they were inserted.
So I went into good ol' SQL Management Studio and asked to make a trigger. It gave me some sample code and here is my Pseudo Code below:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TRIGGER ChangeProvider
ON FlightData
AFTER INSERT
AS
BEGIN
IF(TheInsertedValue == Criteria)
UPDATE FlightData
SET TheInsertedValue = NewValue
ENDIF
END
GO
I am not that good with this type of Database Programming so excuse my mistakes.
How would I go about doing this?
You could add a computed column to your table instead of adding a trigger.
Then the new column could just use a case statement to either show
the original TourOperator column value or the new value you wanted.
You'd add a new column to your table like this
TourOperatorCorrect = CASE WHEN TourOperator = 'Whatever value' THEN 'ChangedValue'
--I just want to use what I have already in the TourOperator column
ELSE TourOperator
END AS VARCHAR(50)
Basics of computed columns are here - https://msdn.microsoft.com/en-ie/library/ms188300.aspx
Your misconception here is that the trigger runs once per inserted value - it is in fact run once per insert statement, so you can and will find more than one row inserted at once.
You'll find that your inserted values are in the pseudo table inserted, which has the same structure as your FlightData table in this case. You write a select statement against that, specifying any criteria you wish.
However, it's not immediately clear what your logic is - does the FlightData table you are updating in your trigger only have one row? Do you update every row in the table with the newest inserted value? It is hard to understand what you are trying to now, and what the purpose of the table and this trigger are - let alone what you would want to do if you inserted more than one row at once.
When inserted table contains mutiple rows,your code will fail,so change code to work with inserted table as whole
UPDATE F
SET f.TheInsertedValue = i.value
from inserted i
join
Flighttable F
on f.matchingcolumn=i.matchingcolumn
and i.somevalue='criteria'
I'm trying to create a temporary table in Postgres (to speed up joining, as there will be a lot of similar queries throughout a session). The SQL that will be called at the beginning of a session is the following:
CREATE TEMPORARY TABLE extended_point AS
SELECT (
point.id,
local_location,
relative_location,
long_lat,
region,
dataset,
region.name,
region.sub_name,
color,
type)
FROM point, region, dataset
WHERE point.region = region.id AND region.dataset = dataset.id;
The tables point has the columns id::int, region::int, local_location::point, relative_location::point, long_lat:point (longitude, latitude).
Region has the columns id::int, color::int, dataset::int, name::varchar, sub_name::varchar.
Dataset has the columns id::int, name::varchar, type:varchar.
When this is run, I get the error message: [25P02] ERROR: current transaction is aborted, commands ignored until end of transaction block.
As a side, the commands are executed in PyCharm, and is part of a Python project.
Any suggestions?
Thanks in advance :)
There is an important difference between these two queries:
select 1, 'abc';
select (1, 'abc');
The first query returns one row with two columns with values 1 and 'abc'. The second one returns a row with one column of pseudo-type record with value (1, 'abc').
Your query tries to create a table with one column of pseudo-type record. This is impossible and should end with
ERROR: column "row" has pseudo-type record
SQL state: 42P16
Just remove brackets from your query.
As a_horse stated, [25P02] ERROR does not apply to the query in question.
Btw, my advice: never use keywords as table/column names.
I want to update or insert a row in a table. I have also created an index on the column I am searching for in the WHERE clause.
The thing I want to insert into the table may or may not already exist in the table so it may be an update or an insert.
So first I define a Boolean variable like "already_exists" and a select statement that goes and searches for the value in the table, if it finds it it will set the Boolean variable to true, else it will remain false.
Then I say oh OK if that variable is true, then run this update command on the table, if it is false run this insert command.
So is it the right way of doing it or there are better ways?
Yes.
Depending on your SQL platform, MERGE or UPSERT...
wikipedia Merge (SQL)