DECLARE #temp_table TABLE (order_no int, username nvarchar(100))
INSERT INTO #temp_table(order_no, username)
SELECT TOP 10
user_id, username
FROM users
ORDER BY user_id
SELECT * FROM #temp_table
Will the rows in #temp_table always be ordered?
The order is never guaranteed unless you explicitly use ORDER BY.
The reason that we can't guarantee the order of a variable table is because there is no default primary key, so if you add an auto incremented key which will serve as the default key then it will always follow the order of this default key. In other words, it will follow the order of insertion.
I.E.
DECLARE #temp_table TABLE (tempid int IDENTITY(1,1), order_no int, username nvarchar(100))
Related
I need some help with the below query where the last step of
Select * from #PersonDetail order by....
is taking so long to execute - why?
There are millions of records being inserted in this temp table #PersonDetail and insert process takes a few seconds, but the last Select from this same temp table is taking so long.
I created a unique clustered index on the columns used for order by and tried many other options but it doesn't make any difference in the performance.
It is a big stored procedure with many temp table but it is this last select step which is impacting the performance. Here is an example of the last step of the query:
DROP TABLE IF EXISTS #PersonDetail
CREATE TABLE #PersonDetail
(
PersonId INT NOT NULL,
Name NVARCHAR(50) NULL,
Number INT NOT NULL,
Tag NVARCHAR(50) NULL,
UserId INT NOT NULL,
NumberEncrypted VARCHAR(100),
Type NVARCHAR(255),
Status NVARCHAR(50),
CreatedDate DATETIMEOFFSET(7),
AddressDetailId NVARCHAR(50),
Category NVARCHAR(50),
PrimaryId INT,
DailyAmount MONEY,
UNIQUE (PersonId UserId),
UNIQUE CLUSTERED(CreatedDate, UserId)
)
INSERT INTO #PersonDetail (PersonId, Name, Number, Tag, UserId, NumberEncrypted,
Type, Status, CreatedDate, AddressDetailId, Category, PrimaryId, Amount)
SELECT
PersonId, Name, Number, Tag, UserId, NumberEncrypted,
Type, Status, CreatedDate, AddressDetailId, Category, PrimaryId, DailyAmount
FROM
#User u
JOIN
dbo.DailyAmount da (NOLOCK) ON da.UserId = u.UserId
SELECT *
FROM #PersonDetail pd
ORDER BY CreatedDate, UserId
You must specify what database are you using.
In general, you must do theese things:
create some indexes on the join columns (DailyAmount.userId, User.userID); how to create the index must change;
create an index on the order by columns, (CreatedDate+UserID); this must change, in postgresql for example an index with the 2 column is better than 2 indexes;
If your data are not changing frequently, you could try materialized view and create the indexes on the materialized view.
I have an existing table with existing data and I want to add new column (named ID) with auto-increment and I want to add a unique value for each row.
Is there an other way than fetching all data and do an update for each row to set this value ?
If you need it in a SELECT:
SELECT *, ROW_NUMBER() OVER(ORDER BY ...A ORDER VALUE) as id
FROM yourTable
If you need it in your table:
ALTER TABLE yourTable ADD id int identity(1,1)
Here is a demo for the output of the ALTER TABLE:
CREATE TABLE #temp(name nvarchar(50))
INSERT INTO #temp(name) VALUES(N'Kai'),(N'Bernd'),(N'Flo'),(N'Pete')
SELECT * FROM #temp
-- This is what you need to do
ALTER TABLE #temp
ADD id int identity(1,1) -- This will add and fill the new column
SELECT * FROM #temp
DROP TABLE #temp
I have this following sql script
DECLARE #tmpTable TABLE (rowID int IDENTITY,
woID varchar(100), srID varchar(100),
woWorkOrderNumber varchar(100),
woSequenceCount varchar(100),
WorkOrderNumber varchar(100)
)
INSERT INTO #tmpTable (woID, srID, woWorkOrderNumber, woSequenceCount, WorkOrderNumber)
SELECT
woID, srID, woWorkOrderNumber, woSequenceCount,
SUBSTRING(woWorkOrderNumber, 11, 20 ) AS WorkOrderNumber
FROM
WorkOrder
WHERE
codeSICurrentStatusCode NOT IN (3, 4)
AND SUBSTRING(woWorkOrderNumber, 11, 20) = ''
SELECT * FROM #tmpTable
But I'm getting these results on my rowID column:
As you can see, the rowID seems to be the row number from the table I selected on. What I'm trying to achieve on this temp table is that the rowID starts from 1 then 2 then 3 and so on and so forth.. What's wrong with my code?
You need to specify ORDER BY on the INSERT statement SELECT clause in order to control the order of identity value assignment. You can alternatively use ROW_NUMBER() instead of IDENTITY to ensure there are no gaps and provide complete control over the values.
I want to insert multiple values into a row, but I want to make sure that the row is unique, i.e. no duplicate rows.
I am unsure how to do this (it is fairly easy to if there is only a single value to check for i.e. like this: SQL Server - How to insert a record and make sure it is unique).
This is my code, but it won't allow me to insert unique rows as it tests for single columns and multiple columns combined.
CREATE TABLE myCities (
UserID int null,
CityID int null
)
DECLARE #UserID int, #CityID int
SET #UserID = 1
SET #CityID = 1
INSERT INTO myCities (UserID,CityID)
SELECT #UserID,#CityID
WHERE
#UserID NOT IN ( SELECT UserID FROM myCities WHERE UserID = #UserID )
AND
#CityID NOT IN ( SELECT CityID FROM myCities WHERE CityID = #CityID )
The only sure way is to put the check in the database. In this case create a unique key on the table which will also be its primary key so
-- syntax for MS/Sybase at least is
ALTER TABLE myCities
ADD CONSTRAINT uc_myCities UNIQUE (UserID,CityID)
Then when you insert a duplicate then you will get an error and your code will have to deal with it.
Sometimes the obvious is right at hand - solved it by using NOT EXISTS, like this:
INSERT INTO myCities (UserID,CityID)
SELECT #UserID,#CityID
WHERE NOT EXISTS (
SELECT UserID FROM myCities
WHERE
UserID = #UserID and
CityID = #CityID
)
I'm writing a SQL script to generate test data for our database. I'm generating the data in table variables (so I can track it later) and then inserting it into the real tables. The problem is, I need to track which rows I've added to the parent table, so that I can generate its child data later on in the script. For example:
CREATE TABLE Customer (
CustomerId INT IDENTITY,
Name VARCHAR(50)
)
CREATE TABLE Order (
OrderId INT IDENTITY,
CustomerId INT,
Product VARCHAR(50)
)
So, in my script, I create equivalent table variables:
DECLARE #Customer TABLE (
CustomerId INT IDENTITY,
Name VARCHAR(50)
) -- populate customers
DECLARE #Order TABLE (
OrderId INT IDENTITY,
CustomerId INT,
Product VARCHAR(50)
) -- populate orders
And I generate and insert sample data into each table variable.
Now, when I go to insert customers from my table variable into the real table, the CustomerId column in the table variable will become meaningless, as the real table has its own identity seed for its CustomerId column.
Is there a way I can track the new identity of each row inserted into the real table, in my table variable, so I can use a proper CustomerId for the order records? Or, is there a better way I should be going about this?
(Note: I originally started with an application to generate the test data, but it ran too slow during insert as > 1,000,000 records need to be generated.)
WHy do you need identity values on the table variables? If you use just int, you can isnert the ids after the insert is done. Grab them using the output clause. YOu might need an input values and an output values table varaiable to get this just right like this:
DECLARE #CustomerInputs TABLE (Name VARCHAR(50) )
DECLARE #CustomerOutputs TABLE (CustomerId INT ,Name VARCHAR(50) )
INSERT INTO CUSTOMERS (name)
OUTPUT inserted.Customerid, inserted.Name INTO #CustomerOutputs
SELECT Name FROM #CustomerInputs
SELECT * from #CustomerOutputs
You can insert the data to the table with a cursor and use the built-in function SCOPE_IDENTITY() to get the last id which was inserted in the current scope (by your script).
See this MSDN article for more information on SCOPE_IDENTITY.
Here is one way of doing it. If you can use it depends on your situation. You should not do it in production environment when users use your db.
-- Get the next identity values for Customer and Order
declare #NextCustomerID int
declare #NextOrderID int
set #NextCustomerID = IDENT_CURRENT('Customer')+1
set #NextOrderID = IDENT_CURRENT('Order')+1
-- Create tmp tables
create table #Customer (CustomerID int identity, Name varchar(50))
create table #Order (OrderID int identity, CustomerID int, Product varchar(50))
-- Reseed the identity columns in temp tables
dbcc checkident(#Customer, reseed, #NextCustomerID)
dbcc checkident(#Order, reseed, #NextOrderID)
-- Populate #Customer
-- Populate #Order
-- Allow insert to identity column on Customer
set identity_insert Customer on
-- Add rows to Customer
insert into Customer(CustomerId, Name)
select CustomerID, Name
from #Customer
-- Restore identity functionality on Customer
set identity_insert Customer off
-- Add rows to Order
set identity_insert [Order] on
insert into [Order](OrderID, CustomerID, Product)
select OrderID, CustomerID, Product
from #Order
set identity_insert [Order] off
-- Drop temp tables
drop table #Customer
drop table #Order
-- Check result
select * from [Order]
select * from Customer
The way I'd do it its first obtain the MAX(CustomerId) from your Customer Table. Then I'd get rid of the IDENTITY column on your variable table and do my own CustomerId using ROW_NUMBER() and the MaxCustomerId. It should be something like this:
DECLARE #MaxCustomerId INT
SELECT #MaxCustomerId = ISNULL(MAX(CustomerId),0)
FROM Customer
DECLARE #Customer TABLE (
CustomerId INT,
Name VARCHAR(50)
)
INSERT INTO #Customer(CustomerId, Name)
SELECT #MaxCustomerId + ROW_NUMBER() OVER(ORDER BY SomeColumn), Name
FROM YourDataTable
Or insert the values on a temp table, so you can use the same ids to fill your Order table.