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Index Scans and Table Scans

There are several things that you can do to improve performance by throwing more hardware at the problem, but usually the place you get the most benefit from is when you tune your queries. One common problem that exists is the lack of indexes or incorrect indexes and therefore SQL Server has to process more data to find the records that meet the queries criteria. These issues are known as Index Scans and Table Scans.

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Purging Data from a Large Table in SQL Server

Purging data from a table is a common database maintenance task to prevent it from growing too large or to stay in compliance with data retention. When dealing with small amounts of data, this can be accomplished by a simple delete with no issues; however, with larger tables, this task can be problematic. Deleting records requires a lock that can block other processes from writing or even reading the data (depending on your isolation level). In this article I will share a technique I have used to work with some very large tables.

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Question of the Day

Changing the Schema

I set up a few users on my SQL Server 2022 instance.

CREATE LOGIN User1 WITH PASSWORD = 'Demo12#1'
CREATE USER User1 FOR LOGIN User1
GO
CREATE LOGIN User2 WITH PASSWORD = 'Demo12#2'
CREATE USER User2 FOR LOGIN User2
GO
CREATE LOGIN User3 WITH PASSWORD = 'Demo12#3'
CREATE USER User3 FOR LOGIN User3
GO
I then created a schema that one of them owned. Under this schema, I added a table with some data.
CREATE SCHEMA MySchema AUTHORIZATION User1
GO
CREATE TABLE Myschema.MyTable(myid INT)
GO
INSERT MySchema.MyTable
(
    myid
)
VALUES
(1), (2), (3)
GO
SELECT * FROM MySchema.MyTable
GO
I granted rights and verified that User2 could access this table.
GRANT SELECT ON Myschema.MyTable TO User2
GO
SETUSER 'USER2'
GO
SELECT * FROM MySchema.MyTable
GO
This worked. Now, I move this schema to a new user.
ALTER AUTHORIZATION ON SCHEMA::Myschema TO User3;
GO
What happens with this code?
SETUSER 'USER2'
GO
SELECT * FROM MySchema.MyTable
GO

See possible answers