# Look up values from a reference table Join / lookup enrich from a reference table Page: ## Status Runs as a SQL step. arcform carries it as a `sql:` step today. ## The DuckDB step enrich with a default when the key is missing It reads the `orders` and `customers` tables the proofs share. Create them first: ```sql CREATE TABLE orders AS SELECT * FROM (VALUES (1, 'Alice Ng', 'north', DATE '2026-01-03', 120.00, 'widget', 'a|b', '{"channel":"web","items":[1,2]}'), (2, 'alice ng', 'north', DATE '2026-01-05', 80.50, 'gadget', 'b', '{"channel":"shop","items":[3]}'), (3, 'Bob Okafor', 'south', DATE '2026-01-05', 300.00, 'widget', 'a|c', '{"channel":"web","items":[4,5,6]}'), (4, 'Carla Díaz', 'east', DATE '2026-01-09', NULL, 'gizmo', NULL, '{"channel":"web","items":[]}'), (5, 'Bob Okafor', 'south', DATE '2026-01-12', 45.25, 'gadget', 'c', '{"channel":"phone","items":[7]}'), (6, 'Dev Patel', 'west', DATE '2026-01-12', 510.00, 'widget', 'a', '{"channel":"web","items":[8,9]}'), (7, 'Carla Diaz', 'east', DATE '2026-01-20', 99.99, 'gizmo', 'b|c', '{"channel":"shop","items":[10]}'), (8, 'Dev Patel', 'west', DATE '2026-02-02', 510.00, 'widget', 'a', '{"channel":"web","items":[8,9]}'), (9, 'Eve Larsen', NULL, DATE '2026-02-03', 15.00, 'gadget', NULL, '{"channel":"web","items":[11]}'), (10, 'Alice Ng', 'north', DATE '2026-02-10', 220.00, 'gizmo', 'a|b|c', '{"channel":"phone","items":[12,13]}') ) t(order_id, customer, region, order_date, amount, product, tags, meta); CREATE TABLE customers AS SELECT * FROM (VALUES ('Alice Ng', 'retail', DATE '2025-06-01', 52.52, 13.40), ('Bob Okafor', 'wholesale', DATE '2025-09-15', 48.85, 2.35), ('Carla Diaz', 'retail', DATE '2025-11-30', 40.42, -3.70), ('Frank Moore', 'retail', DATE '2026-01-01', 51.51, -0.13) ) t(customer, segment, joined, lat, lon); ``` Then run the statement: ```sql CREATE TEMP TABLE result AS SELECT o.order_id, o.customer, coalesce(c.segment, 'unassigned') AS segment FROM orders o LEFT JOIN customers c USING (customer); SELECT * FROM result; SELECT CASE WHEN ((SELECT count(*) = 10 AND count(*) FILTER (WHERE segment = 'unassigned') = 6 AND max(segment) FILTER (WHERE order_id = 6) = 'unassigned' FROM result)) THEN 'as expected' ELSE error('an order with no match did not take the default') END AS verdict; ``` It needs nothing installed beyond DuckDB itself. ## Variants - Add columns from a reference table by key: Match each row to a reference table on a key and append the matching row's columns, keeping every input row. - [Look up with a query for each row](https://meridian.online/operations/look-up-values-from-a-reference-table/look-up-with-a-query-for-each-row): Run a subquery or parameterised query for each input row and attach what it returns. - Append data from a reference service: Add columns from a vendor dataset, reconciliation service or reference index matched to each row. - Replace text using a dictionary table: Find text from a second table in each value and replace it with that table's entry. ## What other tools call it Meridian's classification; an independent blind rating agreed on 86.2% of 312 rows (exact class, version 2). - Azure Data Factory: [`Cached lookup functions`](https://learn.microsoft.com/en-us/azure/data-factory/data-flow-cached-lookup-functions) (read 2026-09-27) - Azure Data Factory: [`Lookup`](https://learn.microsoft.com/en-us/azure/data-factory/data-flow-lookup) (read 2026-09-27) - Alteryx Designer: [`Allocate Append`](https://help.alteryx.com/current/en/designer/tools/demographic-analysis/allocate-append-tool.html) (read 2026-09-27) - Alteryx Designer: [`Calgary Cross Count Append`](https://help.alteryx.com/current/en/designer/tools/calgary/calgary-cross-count-append-tool.html) (read 2026-09-27) - Alteryx Designer: [`Cluster Code`](https://help.alteryx.com/current/en/designer/tools/behavior-analysis/cluster-code-tool.html) (read 2026-09-27) - Alteryx Designer: [`Find Replace`](https://help.alteryx.com/current/en/designer/tools/join/find-replace-tool.html) (read 2026-09-27) - Alteryx Designer: [`Marketo Append`](https://help.alteryx.com/current/en/designer/tools/connectors/marketo-append-tool.html) (read 2026-09-27) - Apache DataFusion: [`Correlated subqueries`](https://datafusion.apache.org/user-guide/sql/subqueries.html) (read 2026-09-27) - Apache DataFusion: [`LATERAL JOIN`](https://datafusion.apache.org/user-guide/sql/select.html) (read 2026-09-27) - Apache DataFusion: [`Scalar subqueries`](https://datafusion.apache.org/user-guide/sql/subqueries.html) (read 2026-09-27) - Duckle: [`Lookup`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25) - Duckle: [`Map`](https://github.com/slothflowlabs/duckle/blob/f85f8960edfb6efbf4cb89d58a7b32e16df0e867/website/docs/components.html) (read 2026-09-25) - EasyMorph: [`Lookup`](https://help.easymorph.com/doku.php?id=transformations:lookup) (read 2026-09-27) - EasyMorph: [`Match`](https://help.easymorph.com/doku.php?id=transformations:match) (read 2026-09-27) - AWS Glue: [`Lookup`](https://docs.aws.amazon.com/glue/latest/dg/transforms-lookup.html) (read 2026-09-27) - Apache Hop: [`Database Join`](https://hop.apache.org/manual/latest/pipeline/transforms/databasejoin.html) (read 2026-09-27) - Apache Hop: [`Database Lookup`](https://hop.apache.org/manual/latest/pipeline/transforms/databaselookup.html) (read 2026-09-27) - Apache Hop: [`Dynamic SQL row`](https://hop.apache.org/manual/latest/pipeline/transforms/dynamicsqlrow.html) (read 2026-09-27) - Apache Hop: [`Stream Lookup`](https://hop.apache.org/manual/latest/pipeline/transforms/streamlookup.html) (read 2026-09-27) - KNIME Analytics Platform: [`Value Lookup`](https://api.hub.knime.com/nodes/*S2w-f2z3562iiLac?details=full) (read 2026-09-27) - Apache NiFi: [`FetchDistributedMapCache`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.FetchDistributedMapCache/) (read 2026-09-27) - Apache NiFi: [`ISPEnrichIP`](https://nifi.apache.org/components/org.apache.nifi.processors.ISPEnrichIP/) (read 2026-09-27) - Apache NiFi: [`JoinEnrichment`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.JoinEnrichment/) (read 2026-09-27) - Apache NiFi: [`Lookup services (family)`](https://nifi.apache.org/components/) (read 2026-09-27) - Apache NiFi: [`LookupAttribute`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.LookupAttribute/) (read 2026-09-27) - Apache NiFi: [`LookupRecord`](https://nifi.apache.org/components/org.apache.nifi.processors.standard.LookupRecord/) (read 2026-09-27) - OpenRefine: [`Add columns from reconciled values…`](https://openrefine.org/docs/manual/reconciling#add-columns-from-reconciled-values) (read 2026-09-27) - OpenRefine: [`cross(cell, s projectName (optional), s columnName (optional))`](https://openrefine.org/docs/manual/grelfunctions#other-functions) (read 2026-09-27) - Pentaho Data Integration: [`Database join`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27) - Pentaho Data Integration: [`Database lookup`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27) - Pentaho Data Integration: [`Dynamic SQL row`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27) - Pentaho Data Integration: [`Stream lookup`](https://docs.pentaho.com/pdia-data-integration/9.3-data-integration/pdi-transformation-steps-reference-overview) (read 2026-09-27) - RapidMiner Studio: [`Replace (Dictionary)`](https://docs.rapidminer.com/latest/studio/operators/blending/values/replace_dictionary.html) (read 2026-09-27) - Talend: [`tFirstnameMatch`](https://help.qlik.com/talend/en-US/components/8.0/name-standardization/name-standardization-component) (read 2026-09-27) - Talend: [`tSynonymSearch`](https://help.qlik.com/talend/en-US/components/8.0/synonym-index/synonym-index-component) (read 2026-09-27) - VisiData: [`join-cols-extend`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/join.py#L423) (read 2026-09-23) - VisiData: [`join-selected-extend`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/join.py#L420) (read 2026-09-23) - VisiData: [`join-sheets-all-extend`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/join.py#L422) (read 2026-09-23) - VisiData: [`join-sheets-top2-extend`](https://github.com/saulpw/visidata/blob/7609212ec2febafa9caba7183cbebfaf49627909/visidata/features/join.py#L421) (read 2026-09-23)