The three questions at the end are worth more than the SQL. Asking what breaks while the old code is still running is how you find out a rename needs two deploys, before you run it and not after.
Prompt
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Write migration [number] that [change].
Produce two SQL blocks:
1. up: the change itself, additive only, including row level security and policies if you create a table.
2. down: the exact reverse, in the order that undoes it.
Then answer in one line each: what happens to existing rows, whether this locks the table, and what breaks if the old code is still running when it lands.
Do not run anything.
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