Skip to main content
Database Administrators

Return to Question

added 260 characters in body
Source Link
cm007
cm007
  • 363
  • 2
  • 3
  • 6

Suppose I have the following long-running query

UPDATE [Table1]
SET [Col1] = 'some value'
WHERE [Col2] = -- some clause which selects thousands of rows

and suppose the following query is executed while the above query is running

SELECT *
FROM [Table1]

Does the first query prevent the second query from running until the first query is done? If so, does the first query prevent the second query from running on all of the rows or just the rows involved in the WHERE clause?

EDIT:

Suppose the second query is

SELECT [Col1], [Col2]
FROM [Table1]
WHERE [Col2] -- some clause whose matching elements overlap those from
             -- the clause in the first query and which has additional matching elements

Suppose I have the following long-running query

UPDATE [Table1]
SET [Col1] = 'some value'
WHERE [Col2] = -- some clause which selects thousands of rows

and suppose the following query is executed while the above query is running

SELECT *
FROM [Table1]

Does the first query prevent the second query from running until the first query is done? If so, does the first query prevent the second query from running on all of the rows or just the rows involved in the WHERE clause?

Suppose I have the following long-running query

UPDATE [Table1]
SET [Col1] = 'some value'
WHERE [Col2] -- some clause which selects thousands of rows

and suppose the following query is executed while the above query is running

SELECT *
FROM [Table1]

Does the first query prevent the second query from running until the first query is done? If so, does the first query prevent the second query from running on all of the rows or just the rows involved in the WHERE clause?

EDIT:

Suppose the second query is

SELECT [Col1], [Col2]
FROM [Table1]
WHERE [Col2] -- some clause whose matching elements overlap those from
             -- the clause in the first query and which has additional matching elements
edited tags
Link
cm007
cm007
  • 363
  • 2
  • 3
  • 6
Tweeted twitter.com/#!/StackDBAs/status/425299490065879040
Source Link
cm007
cm007
  • 363
  • 2
  • 3
  • 6

In SQL Server, how do read locks work?

Suppose I have the following long-running query

UPDATE [Table1]
SET [Col1] = 'some value'
WHERE [Col2] = -- some clause which selects thousands of rows

and suppose the following query is executed while the above query is running

SELECT *
FROM [Table1]

Does the first query prevent the second query from running until the first query is done? If so, does the first query prevent the second query from running on all of the rows or just the rows involved in the WHERE clause?