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

---
title:  Creating Indexes on Map Fields ("Map Indexes")
---

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To assist with the quick lookup of multiple values in a Map (or HashMap) type field, you can create an index (sometimes referred to as a "map index") on specific (or all) keys in that field.

For example, you could create a map index to support the following query:

``` pre
SELECT * FROM /users u WHERE u.name['first'] = 'John' OR u.name['last'] = 'Smith'
```

The map index extends regular range indexes created on single key by maintaining indexes for other specified keys, or for all keys if `*` is used. The underlying structure of the map index can be thought of as a wrapper around all these indexes.

The following Java code samples provide examples of how to create a map index:

``` pre
QueryService qs = cache.getQueryService();

//This will create indexes for for keys 'PVTL' and 'VMW'
qs.createIndex("indexName", "p.positions['PVTL', 'VMW']", "/portfolio p");
```

``` pre
QueryService qs = cache.getQueryService();

//This will create indexes for all keys
qs.createIndex("indexName", "p.positions[*]", "/portfolio p");
```

In gfsh, the equivalents are:

``` pre
gfsh>create index --name="IndexName" --expression="p.positions['PVTL', 'VMW']" --region="/portfolio p"

gfsh>create index --name="IndexName" --expression="p.positions[*]" --region="/portfolio p"
```

In order to create or query a map index, you must use the bracket notation to list the map field keys you wish to index or query. For example: `[*]`, `['keyX1','keyX2’]`. Note that using `p.pos.get('keyX1')` will not create or query the map index.

**Note:**
You can still query against Map or HashMap fields without querying against a map index. For example, you can always create a regular range query on a single key in any Map or HashMap field. However, note that subsequent query lookups will be limited to a single key.

**Note:**
Map indexes on all keys (when `*` is specified) are not used in queries where the map field is compared with `null` or when it is compared using `!=`, e.g. `p.positions['company1'] = null` or `p.positions['company1'] != '3'`.
These types of queries will be executed without making use of the index, which could make them slower.