is there any difference between the follow exemples?
ProjNum int CONSTRAINT nn_ProjNum NOT NULL CONSTRAINT C_ProjNum CHECK (ProjNum >= 10)
ProjNum int NOT NULL CHECK (ProjNum >= 10)
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There is no difference in SQL Server between those two statements. Each results in NOT NULL column (not a constraint) with a single check constraint. The only difference is that second one creates a system-named check constraint, something like 'CK__t__ProjNum__4AB81AF0'.
Both are same.
In my understanding ,
CONSTRAINT CHECK can be define when you add new columns.
ALTER TABLE dbo.DocExc ADD ColumnD int NULL CONSTRAINT CHK_ColumnD_DocExc CHECK (ColumnD > 10 AND ColumnD < 50); GO
Also user can provide own constraint name.
But if we have to put check in existing column then
ALTER TABLE dbo.DocExc ADD CHECK (ExistsColumn > 10 AND ExistsColumn < 50); GO
system will provide constraint name here.