---
title: "joins-syntax"
slug: "joins-syntax"
updated: 2022-12-13T02:18:50Z
published: 2022-12-13T02:18:50Z
canonical: "code.tag.bio/joins-syntax"
---

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

# joins

The `joins` attribute is an array of **table** objects, or references to files containing **table** objects.

Data from *joined tables* will be appended to each line of the *parent table* for processing by parsers.

To preserve system memory when loading data, the `columns` array is required.

```
{
  "table": "~/dir_with_source_data/tttt.csv",
  "table_alias": "tttt",
  "joins": [ 
    {
      "table": "~/dir_with_source_data/jjjj.csv", 
      "table_alias": "jjjj", 
      "id_columns": { 
        "jjj1": "ttt1"
      },
      "columns": [ 
        "jjj1",
        "jjj2",
        "jjj3"
      ]
    }
  ]
}
```

## id_columns

**usage: *required*** The `id_columns` object is a key, value pair of strings which defines the columns used to connect two data sources. The **key** of this object is a column within the joined table and the **value** is a column within the parent table.

## columns

**usage: *required*** This `columns` attribute is an array of strings which reference column names in the source data to include during data loading.