批量更新所有行

Question

I'm new to Sqlite and I have a 15GB database. I need to update all rows in column "filename" in 2 of the tables such that the filename is truncated. Table 1 has 50,000 rows and Table 2 has 25 million rows.

I know the update command for sqlite but I want to find out if using this is advisable in terms of the time it will take and things that can go wrong.
I plan to use these commands:

UPDATE users SET filename=substr(filename,15)
UPDATE people SET filename=substr(filename,15)

Specifically:

1. How long will this take?
2. Should my computer have some minimum configuration for it to work well?
3. Is there a way for me to undo my update in case things go
   horribly wrong like version control?
4. Are there better ways out there of changing all rows in a sqlite database?

Thank you so much!

Answer 1

Rewriting everything will take a long time.

You do not need much memory (although more helps for caching), but you need enough disk space for both the old and new data.

By default, SQLite uses automatic transactions, which prevent partial changes when some statement is interrupted in the middle, but commits at the end of each statement. To be able to check the changes and to commit or roll them back later, use an explicit transaction .