Andrew Farries f2bb2f9581 Make set_unique operations respect the contract for old schema versions (#118) ... When `pg-roll` makes a schema change, the contract with the user is that it will leave the old version of schema unchanged. When the operation to add a `UNIQUE` constraint was implemented (https://github.com/xataio/pg-roll/pull/53), this contract was not respected. The operation adds a unique index to the existing column, changing the behaviour for users of the old schema. This PR changes the operation so that it follows a similar pattern to other operations that were implemented later: * On `Start`: * Duplicate the column. * Add a `UNIQUE` index concurrently * Create `up` and `down` triggers to copy values between the old and new columns. * Backfill values from the old column into the new using `up` SQL * On `Complete` * Create a unique constraint on the new column using the unique index. * Drop the old column * Rename the column to its old name. * Remove `up` and `down` triggers. Writing correct `up` SQL for the operation is a little more difficult than for other operations (eg set `NOT NULL`) as it is up to the user to ensure uniqueness of values. The example migration in this PR appends a random suffix to each value.		2023-09-22 08:52:15 +00:00
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migrations	Make set_unique operations respect the contract for old schema versions (#118)	2023-09-22 08:52:15 +00:00
roll	Rollback operation on Start failure (#73)	2023-09-06 05:42:40 +01:00
schema	Remove unused Schema.Replace method (#78)	2023-09-01 13:38:53 +01:00
state	Allow to migrate existing databases (#112)	2023-09-21 22:41:38 +02:00