ALTER
ALTER is the command used to add, edit, and modify data objects like tables, databases, and views. ALTER is the command responsible for making table column adjustments or renaming table columns. New table columns can also be added and dropped from existing SQL tables.
CONSTRAINT
CONSTRAINT are used to limit the type of data that can go into a table.
Constraints can be specified when a table is created (with the CREATE TABLE statement) or after the table is created (with the ALTER TABLE statement).
ALTER CONSTRAINT
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