geode-docs/developing/query_index/using_indexes_with_equijoin_queries.html.md.erb

---
title:  Using Indexes with Equi-Join Queries
---

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Equi-join queries are queries in which two regions are joined through an equality condition in the WHERE clause.

<a id="concept_A90C5FD84FCB45B2B28D6CE78DE1D117__section_47CFF4EF4D964FCFBB772B0347C02214"></a>
To use an index with an equi-join query:

1.  Create an index for each side of the equi-join condition. The query engine can quickly evaluate the query's equi-join condition by iterating over the keys of the left-side and right-side indexes for an equality match.

    **Note:**
    Equi-join queries require regular indexes. Key indexes are not applied to equi-join queries.

    For this query:

    ``` pre
    SELECT DISTINCT inv.name, ord.orderID, ord.status 
    FROM /investors inv, /orders ord 
    WHERE inv.investorID = ord.investorID 
    ```

    Create two indexes:

    | FROM clause    | Indexed expression |
    |----------------|--------------------|
    | /investors inv | inv.investorID     |
    | /orders ord    | ord.investorID     |

2.  If there are additional, single-region queries in a query with an equi-join condition, create additional indexes for the single-region conditions only if you are able to create at least one such index for each region in the query. Any indexing on a subset of the regions in the query will degrade performance.

    For this example query:

    ``` pre
    SELECT DISTINCT *
    FROM /investors inv, /securities sc, inv.heldSecurities inv_hs
        WHERE sc.status = "active"
        AND inv.name = "xyz"
        AND inv.age > 75
        AND inv_hs.secName = sc.secName
    ```

    Create the indexes for the equi-join condition:

    | FROM clause                                | Indexed expression |
    |--------------------------------------------|--------------------|
    | /investors inv, inv.heldSecurities inv\_hs | inv\_hs.secName    |
    | /securities sc                             | sc.secName         |

    Then, if you create any more indexes, create one on `sc.status` and one on `inv.age` or `inv.name` or both.