He demos a migration script that can deploy such changes safely. You might also learn that in an archaic form of the Scots language, used in Cumberland, the number 17 is "tiny bumfit"; I think the tiny bumfit bus goes from Penrith to Carlisle. It is a common ritual when designing a database to add or remove NULL constraints, but there are a couple of problems that can cause you grief when you are making changes to already-populated tables.
We have a table, CountingWords , in which we record the words used to count, in Old Welsh. We have ambitions to count all the way up to 20, but currently only know how to count to Having released the first version of this table, we realize quickly that we really should have recorded the name of the language, so we alter the design of the table to add a TheLanguage column, which cannot accept NULL s.
We need to take precautionary steps. First, we must remove any existing NULL s explicitly, by updating all the rows with the default value:. Here is the migration script that will either migrate CountingWords from v1 to v2 or else create v2 from scratch, and which will cause no harm if accidentally re-run.
Before you try it, either drop the CountingWords table, or rerun Listing 1 to reestablish v1 of the table. I just hate build scripts that can only be run in particular circumstances. What a shame, but then we can now test out our foreign key constraint. Apologies to Stateside friends and relatives that I left out the several Indian tribes who used the same counting rhymes. These are techniques for making changes to existing tables, which is why I elaborated the demonstration to illustrate how to go about doing both of these operations as part of a resilient script that can be run regardless of whether it is a fresh build or a migration, and that can be re-run without any detrimental effects.
I got an error that indicated that the table needed to be dropped and re-created. Igor S. Cool, you don't have to specify the data-type, just "null" to make it nullable. Hammerite Hammerite Rodrigo Itursarry Rodrigo Itursarry 21 2 2 bronze badges. Does this answer bring anything new with respect to IgorS's answer? Libor B. You have to create a new column, migrate the data, and then drop the column: -- 1. Migrate data - you need to write code for that -- 4. Martin Thoma Martin Thoma k gold badges silver badges bronze badges.
Hybris95 2, 2 2 gold badges 14 14 silver badges 33 33 bronze badges. Please add code type notation for your answer and some describe about this — Amirhossein.
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Add a comment. Active Oldest Votes. Improve this answer. Alex Logvin 6 6 silver badges 11 11 bronze badges. Wil Wil 3, 1 1 gold badge 14 14 silver badges 14 14 bronze badges. Sure you can. Mark S. Rasmussen Mark S. Rasmussen Viewed 1.
Using SQL server Improve this question. Marko Karmic Coder Karmic Coder 17k 5 5 gold badges 31 31 silver badges 41 41 bronze badges. Add a comment. Active Oldest Votes. Improve this answer. Arsen Khachaturyan 7, 4 4 gold badges 36 36 silver badges 38 38 bronze badges.
Let me value-add to the above two correct responses. The semantics of NULL can have a few meanings. Before you did the above recommendations.
Make sure you application does not take null in its business logic. Backup your database first in case you make a typo and your DB explodes. Databases should always be backed up. SebastianGodelet: there's a setting that allows you to turn off that warning, or make it so that it doesn't prevent you from modifying the table. In some cases, changing the schema of a table requires that a new table be created, the data copied over from the old and the old table dropped.
Because an error in this process could result in data loss, SSMS warns you and, by default, prevents you from doing it. Show 2 more comments. Greg Dougherty Greg Dougherty 3, 7 7 gold badges 33 33 silver badges 51 51 bronze badges.
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