SQL Server Modify Table

ALTER TABLE may be done in three different ways.

The first type:

Only metadata is modified.

1. Delete a column.

2, a row is incremented and the null value is considered to be the new value for all rows.

3. When the length of a variable-length column increases.

4. Null is not allowed when the column is allowed to be empty.

The second type:

Check all data to make sure they are compatible with the modifications but only to modify the metadata.

1. You set the empty property to not empty.

2, shorten the variable length.

The third type:

To physically modify each row.

1. Add a column that cannot be considered empty, given a default value.

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SQL Server Modify Table