---
title: "AddJoin"
slug: "addjoin"
updated: 2023-09-20T16:38:38Z
published: 2023-09-20T16:38:38Z
canonical: "docs.datajet.app/addjoin"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.datajet.app/llms.txt
> Use this file to discover all available pages before exploring further.

# AddJoin

Creates a join between two tables.

Notes - tables must be joined to copy fields, calculate aggregates and perform cross-table data set manipulation. Tables can only be joined on one key at a time, although some engineering methods allow an explicit alternative join to be specified.

For more information on joins, see [Joins](/v1/docs/joins)

To build multi-layer joins, see [AddJoinLayer](/v1/docs/addjoinlayer).

| Key | Value(s) | Description |
| --- | --- | --- |
| method | "AddJoin" |  |
| project | "Name of Project" |  |
| primaryTable | "TableName" | Name of Table on the ONE side of a ONE to MANY Join |
| primaryField | "ShortFieldName" | Name of Key Field on the ONE side of a ONE to MANY Join |
| foreignTable | "TableName" | Name of Table on the MANY side of a ONE to MANY Join |
| foreignField | "ShortFieldName" | Name of Key Field on the MANY side of a ONE to MANY Joina |
| fdataset{} | "ForeignTableDataSet" | Added v5.9.16 Optional. Foreign Table dataset. Join will be built from records in the dataset. |

```json
{
  "method": "AddJoin",
  "primaryTable": "coupon response",
  "primaryField": "Transaction ID",
  "foreignTable": "Sales",
  "foreignField": "Transaction ID",
  "project": "BulkDecode"
}
```

The following builds a join using a filtered dataset on the foreign table:

```json
{
  "method": "AddJoin",
  "primaryTable": "BikePoints",
  "primaryField": "commonName_short",
  "foreignTable": "BikeTripData",
  "foreignField": "EndStation_short",
  "project": "BikeData2",
  "fDataSet": {
    "logic": "or",
    "name": "DataSet",
    "strict": true,
    "set": [
      {
        "logic": "and",
        "stype": "FIELD",
        "entity": {
          "type": "field",
          "name": "BikeTripData.Duration",
          "table": "BikeTripData",
          "valueFilter": []
        },
        "op": ">",
        "values": [
          "0"
        ]
      }
    ]
  }
}
```