If you want to disable all constraints in the database just run this code:
-- disable all constraints
EXEC sp_MSforeachtable "ALTER TABLE ? NOCHECK CONSTRAINT all"
To switch them back on, run: (the print is optional of course and it is just listing the tables)
-- enable all constraints
exec sp_MSforeachtable @command1="print '?'", @command2="ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all"
I find it useful when populating data from one database to another. It is much better approach than dropping constraints. As you mentioned it comes handy when dropping all the data in the database and repopulating it (say in test environment).
If you are deleting all the data you may find this solution to be helpful.
Also sometimes it is handy to disable all triggers as well, you can see the complete solution here.
If you are on SQL Server 2017 or Azure, see Mathieu Renda answer.
I had a similar issue when I was trying to join two tables with one-to-many relationships. In SQL 2005 I found that XML PATH
method can handle the concatenation of the rows very easily.
If there is a table called STUDENTS
SubjectID StudentName
---------- -------------
1 Mary
1 John
1 Sam
2 Alaina
2 Edward
Result I expected was:
SubjectID StudentName
---------- -------------
1 Mary, John, Sam
2 Alaina, Edward
I used the following T-SQL
:
SELECT Main.SubjectID,
LEFT(Main.Students,Len(Main.Students)-1) As "Students"
FROM
(
SELECT DISTINCT ST2.SubjectID,
(
SELECT ST1.StudentName + ',' AS [text()]
FROM dbo.Students ST1
WHERE ST1.SubjectID = ST2.SubjectID
ORDER BY ST1.SubjectID
FOR XML PATH ('')
) [Students]
FROM dbo.Students ST2
) [Main]
You can do the same thing in a more compact way if you can concat the commas at the beginning and use substring
to skip the first one so you don't need to do a sub-query:
SELECT DISTINCT ST2.SubjectID,
SUBSTRING(
(
SELECT ','+ST1.StudentName AS [text()]
FROM dbo.Students ST1
WHERE ST1.SubjectID = ST2.SubjectID
ORDER BY ST1.SubjectID
FOR XML PATH ('')
), 2, 1000) [Students]
FROM dbo.Students ST2
Best Answer
It disables foreign keys on the table you are inserting into.
Yes, this is a horrible default. Be sure to set the option
CHECK_CONSTRAINTS
(orCheckConstraints
forSqlBulkCopy
) if you can at all afford it.It also by default does not fire triggers which is equally terrible for data consistency. The triggers are there for a reason.