Build an Update query
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Start with a Select query, add parameters to it, and run it to make sure it returns only the data you want to change.
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Back to Design view, click Update.
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Enter your new value on the Update To row, run the query.
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Click Select, enter the value from step 3 in the Criteria row, run the query to check your changes.
Update multiple fields or tables
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Follow steps 1 and 2 above, but enter criteria in each field or table you want to change, then run the query to make sure you’re seeing just the records you want to change.
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Query design view > Update > new values, run.
Staying out of trouble
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Don’t update calculated fields.
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Don’t update primary keys, unless they’re part of a relationship that allows cascading updates. Also, changes to a primary key cascade to all related foreign keys.
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Don’t update queries set to return unique values.
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Don’t try to update Union queries.