i need some help with a SQL alter command. i am trying to add a field to my table, but when i do the field is filled with null in any existing rows. how can i just make it fill blank like the value ...
> 原文:[https://www . geesforgeks . org/SQL-query-add-unique-key-constraints-using-alter-command/](https://www.geeksforgeeks.org/sql-query-to-add-unique-key ...
The ALTER command in SQL is used to modify the structure of an existing table. It allows you to add, delete, or modify columns, as well as add or drop constraints.
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