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Ian Gulliver
2019-04-24 06:27:20 +00:00
parent e924f0f659
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2011-11-29-safer-data-changes.html
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@@ -10,8 +10,7 @@
<li>Check the SQL files into source control somewhere. Manual changes tend to breed more manual changes to fix the fixes, so you never know when you'll want a record of what you twiddled in the past.</li>
<li>Include all fields from the primary key in the WHERE clause. This ensures that each statement only modifies one row. Even if this results in a huge list of changes, at least you know exactly what changed.</li>
<li>Include as many additional gating clauses as possible, linked with AND. For example, if you have a table of products and you want to set the price to 0.99 for everything that is currently set to 1.00, do:
<code>
UPDATE Products SET Price=0.99 WHERE ProductId=2762 AND Price=1.00;
<code>UPDATE Products SET Price=0.99 WHERE ProductId=2762 AND Price=1.00;
</code>
This ensures that if something else changes Price just before you run your change, you don't destroy that update.</li>
<li>Record the number of rows affected by each statement, in case something unexpected happens.</li>