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(core) Add diff preview to Importer

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Summary:
Updates the preview table in Importer to show a diff of changes
when importing into an existing table and updating existing records.

Test Plan: Browser tests.

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D3060
This commit is contained in:
George Gevoian
2021-10-07 23:32:59 -07:00
parent d635c97686
commit 62db263d1f
8 changed files with 471 additions and 168 deletions
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28
app/server/lib/ExpandedQuery.ts
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@@ -178,14 +178,36 @@ export function buildComparisonQuery(leftTableId: string, rightTableId: string,
);
});
// Join both tables on `joinColumns`, including unmatched rows from `leftTableId`.
/**
* Performance can suffer when large (right) tables have many duplicates for their join columns.
* Specifically, the number of rows returned by the query can be unreasonably large if each
* row from the left table is joined against up to N rows from the right table.
*
* To work around this, we de-duplicate the right table before joining, returning the first row id
* we find for a given group of join column values. In practice, this means that each row from
* the left table can only be matched with at most 1 equivalent row from the right table.
*/
const dedupedRightTableQuery =
`SELECT MIN(id) AS id, ${[...joinColumns.values()].map(v => quoteIdent(v)).join(', ')} ` +
`FROM ${quoteIdent(rightTableId)} ` +
`GROUP BY ${[...joinColumns.values()].map(v => quoteIdent(v)).join(', ')}`;
const dedupedRightTableAlias = quoteIdent('deduped_' + rightTableId);
// Join the left table to the (de-duplicated) right table, and include unmatched left rows.
const joinConditions: string[] = [];
joinColumns.forEach((rightTableColumn, leftTableColumn) => {
const leftExpression = `${quoteIdent(leftTableId)}.${quoteIdent(leftTableColumn)}`;
const rightExpression = `${quoteIdent(rightTableId)}.${quoteIdent(rightTableColumn)}`;
const rightExpression = `${dedupedRightTableAlias}.${quoteIdent(rightTableColumn)}`;
joinConditions.push(`${leftExpression} = ${rightExpression}`);
});
joins.push(`LEFT JOIN ${quoteIdent(rightTableId)} ON ${joinConditions.join(' AND ')}`);
joins.push(
`LEFT JOIN (${dedupedRightTableQuery}) AS ${dedupedRightTableAlias} ` +
`ON ${joinConditions.join(' AND ')}`);
// Finally, join the de-duplicated right table to the original right table to get all its columns.
joins.push(
`LEFT JOIN ${quoteIdent(rightTableId)} ` +
`ON ${dedupedRightTableAlias}.id = ${quoteIdent(rightTableId)}.id`);
// Filter out matching rows where all non-join columns from both tables are identical.
const whereConditions: string[] = [];