# Left join in API queries

The default behavior when an API query is executed is to put in right join the relationship between objects. From DLP 4.0.0 is possible specify in the filters of the API URL query to use left join instead of the right join.

For instance the following API query: [http://platform-dev.dataloy.com/ws/rest/Cargo?pageNumber=1\&limit=50\&filter=voyage.voyageHeader.isBudget(EQ)0\&filter=(OR)\&filter=voyage(NULL)](http://localhost:8080/ws/rest/Cargo?pageNumber=1\&limit=5\&filter=voyage%2B.voyageHeader%2B.isBudget\(EQ\)0\&filter=\(OR\)\&filter=voyage\(NULL\))

generates the following SQL query:

```
SELECT t0.CARGO_ID AS c0
FROM TBL_CARGO t0 JOIN TBL_VOYAGE t1 ON (t0.VOYAGE_ID = t1.VOYAGE_ID) JOIN TBL_VOYAGE_HEADER t2 ON (t1.VOYAGE_ID = t2.VOYAGE_ID)
WHERE ((t2.IS_BUDGET = 0) OR (t0.VOYAGE_ID IS NULL))
```

That will not return cargoes with voyages null.

Instead if the following query is executed: 

[http://platform-dev.dataloy.com/ws/rest/Cargo?pageNumber=1\&limit=50\&filter=voyage**+**.voyageHeader**+**.isBudget(EQ)0\&filter=(OR)\&filter=voyage(NULL)](http://localhost:8080/ws/rest/Cargo?pageNumber=1\&limit=5\&filter=voyage%2B.voyageHeader%2B.isBudget\(EQ\)0\&filter=\(OR\)\&filter=voyage\(NULL\))

encoded (+ become %2B):

[http://platform-dev.dataloy.com/ws/rest/Cargo?pageNumber=1\&limit=50\&filter=voyage**%2B**.voyageHeader**%2B**.isBudget(EQ)0\&filter=(OR)\&filter=voyage(NULL)](http://localhost:8080/ws/rest/Cargo?pageNumber=1\&limit=5\&filter=voyage%2B.voyageHeader%2B.isBudget\(EQ\)0\&filter=\(OR\)\&filter=voyage\(NULL\))

generates the following SQL query:

```
SELECT t0.CARGO_ID AS c0
FROM TBL_CARGO t0 LEFT JOIN TBL_VOYAGE t1 ON (t0.VOYAGE_ID = t1.VOYAGE_ID) LEFT JOIN TBL_VOYAGE_HEADER t2 ON (t1.VOYAGE_ID = t2.VOYAGE_ID)
WHERE ((t2.IS_BUDGET = 0) OR (t0.VOYAGE_ID IS NULL))
```

It will return also cargoes with voyage null.

The same concept is used with **sort**:

Executing this query:

[http://platform-dev.dataloy.com/ws/rest/Cargo?sort=voyage.voyageHeader.referenceNo(AS)](http://localhost:8080/ws/rest/Cargo?sort=voyage%2B.voyageHeader%2B.referenceNo\(AS\))

the following SQL query is executed:

```

SELECT  t0.CARGO_ID  FROM TBL_CARGO t0
     JOIN TBL_VOYAGE t2
    ON (t0.VOYAGE_ID = t2.VOYAGE_ID)
     JOIN TBL_VOYAGE_HEADER t3
    ON (t2.VOYAGE_ID = t3.VOYAGE_ID)
    ORDER BY t3.REFERENCE_NO
```

Instead running the following query:

[http://platform-dev.dataloy.com/ws/rest/Cargo?sort=voyage**%2B**.voyageHeader**%2B**.referenceNo(AS)](http://localhost:8080/ws/rest/Cargo?sort=voyage%2B.voyageHeader%2B.referenceNo\(AS\))

the following SQL query is executed:

```
SELECT  t0.CARGO_ID  FROM TBL_CARGO t0
     LEFT JOIN TBL_VOYAGE t2
    ON (t0.VOYAGE_ID = t2.VOYAGE_ID)
     LEFT JOIN TBL_VOYAGE_HEADER t3
    ON (t2.VOYAGE_ID = t3.VOYAGE_ID)
    ORDER BY t3.REFERENCE_NO
```


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# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://api.dataloy.com/user-guides/left-join-in-api-queries.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.