Summary of SQL massive data operations

20-million data records

Instant change of table name

Instantly changed field name

Moving fields is very slow for 10 minutes. It is better to make a view to rearrange the positions.

Adding an index for 1 minute, but if the table is very busy, it may take a long time (about 15 minutes). So I first changed the table name, added the index, and finally changed the table name back.

1 minute of de-Indexing

Adding a null field is instantaneous because no additional space is required.

Cancelling a null field for 5-10 minutes requires additional space allocation.

The update field with a null value = 'X' depends on the length of X. The longer the value of X, the more time it is used.