feat(bigquery): add migration quickstart

[shollyman]

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[snippet-bot]

Here is the summary of changes.

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• bigquery/bigquery_migration_quickstart/main.go:15, tag bigquerymigration_quickstart

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[tswast]

Is this a GCS path? If so, maybe we could stick something in our sample data bucket?

[shollyman]

Yeah, I've added some resources to the public sample, but I think they still need work.

[tswast]

I'm a bit confused why the API doesn't use a oneof here. Presumably it only supports a limited number of types + detail messages.

[shollyman]

It's because the intent is to allow user extension; so you end up with an arbitrary set of task definitions without a central registry.

[tswast]

Oh dear. No long running operation API?

[shollyman]

Not at alpha at least.

[shollyman]

Filed googleapis/repo-automation-bots#2667 to see what's going on with snippet bot

[shollyman]

Referencing this here since it's not tracked as part of the PR, but it core to the quickstart:

gsutil cat gs://cloud-samples-data/bigquery/migration/translation/input/queries.txt

DATABASE ExampleDatabase;
SELECT * FROM teratable1;
SELECT invalidcolumn, fname FROM teratable2;
INSERT INTO teratable3 (foo, bar, baz) VALUES (1,2,3);

gsutil cat gs://cloud-samples-data/bigquery/migration/translation/schema/ddl.txt

CREATE TABLE teratable1 (code char, examplejson JSON(1000));
CREATE TABLE teratable2 (idx INT, username VARCHAR(64), fname
VARCHAR(100)) UNIQUE PRIMARY INDEX (idx);

[shollyman]

Sample output to GCS:

gsutil cat gs://output prefix omitted/queries.txt

<Translation Failure for query at original line 1, column 1: DATABASE ExampleDatabase;>

-- #Translation Warning# Could not fully verify query, please provide table information for: teratable1
SELECT * FROM teratable1;

-- #Translation Warning# Below Verification Error encountered for translation output. The corresponding input query is at original line 3, column 1.
-- #Translation Warning# Unrecognized name: invalidcolumn [at 1:8]
SELECT invalidcolumn, fname FROM teratable2;

-- #Translation Warning# Could not fully verify query, please provide table information for: teratable3
INSERT INTO teratable3 (foo, bar, baz) VALUES (1, 2, 3);

gsutil cat gs:/output prefix omitted/queries_errors.csv

Input_Query,Line,Column,Category,Message,Type
"DATABASE ExampleDatabase;
",1,1,SqlParseException,Non-query expression encountered in illegal context,ERROR