In my database, i have a trigger which insert the change log entries when a row in Table tblA is updated.
Now, in my code i have to update it through a plain Sql query like
int count = DBContext.ExecuteStoreCommand("<sql query to update records>");
This count variable contains the number of rows affected(no of rows updated + no of rows inserted) due to query.
So my question is, How do i can get only the number of updated rows?
Currently i'm using Entity framework 4. I have looked for solution through connected or disconnected model but couldn't help myself.
int count = DBContext.ExecuteStoreCommand("");
I think you hv to change this to return Select result set
then do this,
<sql query to update>
Select ##RowCount rowcountAffected
Or
suppose your update is
update table1 set col1='foo' where id=2
select count(*) rowcountAffected from table1 where id=2
The most efficient way to return row affected can be
i) Assuming you only update (don't refresh any record after that)
Put Set Nocount ON
Declare #Output parameter inside proc
Related
I have a trigger on a table which gets triggered on any new insert...Here is the code for the trigger. This trigger has to calculate duration in seconds and insert the record in the table.
CREATE TRIGGER duration_trigger
BEFORE INSERT on StudentData
BEGIN
UPDATE StudentData set duration = (select cast( (julianday(enddatetime) - julianday(startdatetime) ) *24 * 60 *60 as integer) from StudentData);
END
In StudentsData table Duration column is defined as INTEGER,
StartDatetime and EndDatetime are defined as TEXT
Here comes my issue.
Trigger gets triggered, but the value in Duration column is always 7
When I execute the same select query that is in the the trigger in a SQL tool, it gives me correct duration in seconds. Trigger on the database is not producing the same result...what could be the issue?
I am also attaching screenshots of the trigger data in the table and select query results from same table.
Table results after trigger.
Select Query results
Basically you are updating all rows as you are not specifying a WHERE clause for the update. So the very last successful update will apply the value to all rows, hence why they are all 7.
Furthermore before you have inserted a row what is there to update? I don't think this can be done an analogy would be; Before you build the wall paint the wall.
Now you could UPDATE after the insert, but care needs to be taken when using UPDATE i.e. if you want to update anything other than all rows then you need to restrict the update to the required rows. A WHERE clause can do this.
As such if you were to ensure that an inserted column were set to an invalid value (as far as your view of the data e.g. a duration of -1 would only suit Dr. Who (apologies to any other Time Travellers)).
Null could also be used.
However, I prefer using a value that is specifically set. Assuming that the row is inserted with duration being given a value of -1 (e.g. duartion INTEGER DEFAULT -1) Then :-
CREATE TRIGGER duration_trigger001
AFTER INSERT on StudentData
BEGIN
UPDATE StudentData SET duration = ((julianday(enddatetime) - julianday(startdatetime)) * 24 * 60 * 60) WHERE duration = -1;
END;
Would work e.g. :-
Notes
The first two rows were added before the trigger was created.
Row 10 was deleted because I used . instead of : as a separator it did nothing.
I didn't cast to INT for simplicity/laziness.
I'm trying to add an auto-calculated field in SQL Server 2012 Express, that stores the % of project completion, by calculating the date difference by using:
ALTER TABLE dbo.projects
ADD PercentageCompleted AS (select COUNT(*) FROM projects WHERE project_finish > project_start) * 100 / COUNT(*)
But I am getting this error:
Msg 1046, Level 15, State 1, Line 2
Subqueries are not allowed in this context. Only scalar expressions are allowed.
What am I doing wrong?
Even if it would be possible (it isn't), it is anyway not something you would want to have as a caculated column:
it will be the same value in each row
the entire table would need to be updated after every insert/update
You should consider doing this in a stored procedure or a user defined function instead.Or even better in the business logic of your application,
I don't think you can do that. You could write a trigger to figure it out or do it as part of an update statement.
Are you storing "percentageCompleted" as a duplicated column value in the same table as your project data?
If this is the case, I would not recommend this, because it would duplicate the data.
If you don't care about duplicate data, try something separating the steps out like this:
ALTER TABLE dbo.projects
ADD PercentageCompleted decimal(2,2) --You could also store it as a varchar or char
declare #percentageVariable decimal(2,2)
select #percentageVariable = (select count(*) from projects where Project_finish > project_start) / (select count(*) from projects) -- need to get ratio by completed/total
update projects
set PercentageCompleted = #percentageVariable
this will give you a decimal value in that table, then you can format it on select if you desire to % + PercentageCompleted * 100
I want to write a stored procedure (SQL server 2008r2), say I have a table:
person
Columns:
Id int (pk)
Date_of_birth date not null
Phone int allow null
Address int allow null
Name nvarchat(50) not null
Sample data:
Id=1,Date_of_birth=01/01/1987,phone=88888888,address=null,name='Steve'
Update statement in Stored procedure, assume
The parameters are already declare:
Update person set
Date_of_birth=#dob,phone=#phone,address=#address,name=#name where id=#id
The table has a trigger to log any changes.
Now I have an asp.net update page for updating the above person table
The question is, if user just want to update address='apple street' , the above update statement will update all the fields but not check if the original value = new value, then ignore this field and then check the next field. So my log table will log all the event even the columns are not going to be updated.
At this point, my solutions
Select all the value by id and store them into local variables.
Using if-else check and generate the update statement. At last,
dynamically run the generated SQL (sp_executesql)
Select all the value by id and store them into local variables.
Using if-else check and update each field seperately:
If #dob <> #ori_dob
Begin
Update person set date_of_birth=#dob where id=#id
End
May be this is a stupid question but please advice me if you have better idea, thanks!
This is an answer to a comment by the OP and does not address the original question. It would, however, be a rather ugly comment.
You can use a statement like this to find the changes to Address within an UPDATE trigger:
select i.Id, d.Address as OldAddress, i.Address as NewAddress
from inserted as i inner join
deleted as d on d.Id = i.Id
where d.Address <> i.Address
One such statement would be needed for each column that you want to log.
You could accumulate the results of the SELECTs into a single table variable, then summarize the results for each Id. Or you can use INSERT/SELECT to save the results directly to your log table.
I have simultaneous request to a particular row in a table and PL/SQL statement is used to update the table by reading the data from master row in the same table and update the current range row and master row it read.
Algorithm is like this:-
Declare
variable declaration
BEGIN
Select (Values) into (values1) from table where <condition1> for update;
select count(*) into tempval from table where <condition2>;
if (tempval == 0) then
insert into table values(values);
else
select (values) into (values2) from table where <condition2> for update;
update table set (values1) where <condition2>;
end if
update table set (values1+incrval) where <condition1>
END;
Unfortunately the master row is updated properly with the correct sequence but the current range picks up the old value of the master range. It does the dirty read. Even though the transaction isolation level for the table is serialized.
Please could some tell me what is happening here?
This is working as designed. Oracle default, and only, read isolation lets the session see all of their own updates. If you perform:
INSERT INTO TABLE1 (col1) values (1);
COMMIT;
UPDATE TABLE1 SET col1 = 2 where col1 = 1;
SELECT col1 FROM TABLE1;
you will see 2 returned from the last query. Please read the Merge Explanation for how to use a MERGE statement to perform the insert or update based upon a single criteria.
I want to get the number of selected rows as well as the selected data. At the present I have to use two sql statements:
one is
select * from XXX where XXX;
the other is
select count(*) from XXX where XXX;
Can it be realised with a single sql string?
I've checked the source code of sqlite3, and I found the function of sqlite3_changes(). But the function is only useful when the database is changed (after insert, delete or update).
Can anyone help me with this problem? Thank you very much!
SQL can't mix single-row (counting) and multi-row results (selecting data from your tables). This is a common problem with returning huge amounts of data. Here are some tips how to handle this:
Read the first N rows and tell the user "more than N rows available". Not very precise but often good enough. If you keep the cursor open, you can fetch more data when the user hits the bottom of the view (Google Reader does this)
Instead of selecting the data directly, first copy it into a temporary table. The INSERT statement will return the number of rows copied. Later, you can use the data in the temporary table to display the data. You can add a "row number" to this temporary table to make paging more simple.
Fetch the data in a background thread. This allows the user to use your application while the data grid or table fills with more data.
try this way
select (select count() from XXX) as count, *
from XXX;
select (select COUNT(0)
from xxx t1
where t1.b <= t2.b
) as 'Row Number', b from xxx t2 ORDER BY b;
just try this.
You could combine them into a single statement:
select count(*), * from XXX where XXX
or
select count(*) as MYCOUNT, * from XXX where XXX
To get the number of unique titles, you need to pass the DISTINCT clause to the COUNT function as the following statement:
SELECT
COUNT(DISTINCT column_name)
FROM
'table_name';
Source: http://www.sqlitetutorial.net/sqlite-count-function/
For those who are still looking for another method, the more elegant one I found to get the total of row was to use a CTE.
this ensure that the count is only calculated once :
WITH cnt(total) as (SELECT COUNT(*) from xxx) select * from xxx,cnt
the only drawback is if a WHERE clause is needed, it should be applied in both main query and CTE query.
In the first comment, Alttag said that there is no issue to run 2 queries. I don't agree with that unless both are part of a unique transaction. If not, the source table can be altered between the 2 queries by any INSERT or DELETE from another thread/process. In such case, the count value might be wrong.
Once you already have the select * from XXX results, you can just find the array length in your program right?
If you use sqlite3_get_table instead of prepare/step/finalize you will get all the results at once in an array ("result table"), including the numbers and names of columns, and the number of rows. Then you should free the result with sqlite3_free_table
int rows_count = 0;
while (sqlite3_step(stmt) == SQLITE_ROW)
{
rows_count++;
}
// The rows_count is available for use
sqlite3_reset(stmt); // reset the stmt for use it again
while (sqlite3_step(stmt) == SQLITE_ROW)
{
// your code in the query result
}