# Use Group and Filter Pre-projection

Improve query performance by moving group and filter operations on simple fields before the `foreach` statement. A simple field is projected as-is and doesn't have additional expressions.

Projection refers to the subset of columns that your query returns. In SAQL, projection occurs in the `foreach` statement, where the query performs an operation on each row in the dataset.

:::note
SAQL supports only pre-projection filters that follow this format: `fieldName operatorName constant`. For example, you can include `q = filter q by Category;`, but not `q = filter q by Discount > 1;`. The same applies to grouping. For example, you can include `q = group q by Category;`, but not `q = group q by Discount > 1;`.
:::

## Example: Filter

In this query, the `filter` statement occurs post-projection.

```nolang
q = load "Superstore";
q = foreach q generate 'Category' as 'Store_Category', 'Sub_Category' as 'Store_Sub_Category';
q = filter q by 'Store_Category'=="Furniture";
```

Here, we move the filter to pre-projection. Because the `Category` field occurs before the `foreach` statement, it doesn't have an alias.

```nolang
q = load "Superstore";
q = filter q by 'Category'=="Furniture";
q = foreach q generate 'Category' as 'Store_Category', 'Sub_Category' as 'Store_Sub_Category';
```

## Example: Group

In this example, the query first creates two new fields: `Detailed_Category`, a combination of the `Category` and `Sub_Category` fields, and `Adjusted_Discount`. After grouping the results by `Detailed_Category`, the second `foreach` statement takes the average of `Adjusted_Discount` for each `Detailed_Category`.

```nolang
q = load "Superstore";
q = foreach q generate 'Category'+ "-" + 'Sub_Category' as 'Detailed_Category', 2*'Discount' as 'Adjusted_Discount';
q = group q by 'Detailed_Category';
q = foreach q generate 'Detailed_Category', avg('Adjusted_Discount') as  'Avg_Adjusted_Discount';

```

Instead of using two `foreach` statements, group by `Sub_Category` pre-projection, and add its alias in the `foreach` statement.

```nolang
q = load "Superstore";
q = group q by ('Category', 'Sub_Category');
q = foreach q generate 'Category'+ "-" + 'Sub_Category' as 'Detailed_Category', 2*avg('Discount') as  'Avg_Adjusted_Discount';
```

**See Also**

- [group-by](/docs/analytics/bi-dev-guide-saql/guide/bi-saql-statement-groupby.md)
- [filter](/docs/analytics/bi-dev-guide-saql/guide/bi-saql-statement-filter.md)