# Non-Spatial Queries <a id="non-spatial-queries"></a>


__🔙[Back to Homepage](../intro.md)__

## Manual selection <a id="manual-selection"></a>

- Select the features manually in the __attribute table__ by clicking on it.
- Holding <kbd>Ctrl</kbd> while selecting features lets you select multiple features at once.

:::{dropdown} Example: Manually select countries with the attribute table
:open:
<video width="100%" controls src="https://github.com/GIScience/gis-training-resource-center/raw/main/fig/en_qgis_select_by_attribute_table_wiki.mp4"></video>
:::

## Select by expression <a id="select-by-expression"></a>

The `Select by Expression` tool lets you build an expression to select features of a layer. For example, you can select specific attributes, or select features where the value of an attribute in a specific range.

1. Open the attribute table and select the `Select by Expression`-tool.

![](../../../fig/en_select_features_expression.png)

2. The expression builder will open.

![](../../../fig/en_query_builder.PNG)



### Comparison operators <a id="comparison-operators"></a>
- `>`, `<`, `=`, `!=`

:::{dropdown} Example: Select all cities with more than 20 million inhabitants in 2015: `"2015" > 20000`
:open:
<video width="100%" controls src="https://github.com/GIScience/gis-training-resource-center/raw/main/fig/en_qgis_select_by_expresion_greater_wiki.mp4"></video>
:::

### Special operators <a id="special-operators"></a>

- `LIKE`

:::{dropdown} Example: Select all countries in Asia: `"continent" LIKE 'asia'`
:open:
<video width="100%" controls src="https://github.com/GIScience/gis-training-resource-center/raw/main/fig/en_qgis_select_by_expression_like_wiki.mp4"></video>
:::

### Logical operators <a id="logical-operators"></a>
- `AND`, `OR`
- Can be used to combine different queries or criteria.

:::{dropdown} Example: Cities, not having a population of one million inhabitants in 1950, had surged to over 10 million inhabitants by 2015: `"1950" < 1000 AND "2015" > 10000`
:open:
<video width="90%" controls src="https://github.com/GIScience/gis-training-resource-center/raw/main/fig/en_qgis_select_by_expression_and_wiki.mp4"></video>
:::

## Complex Expressions <a id="complex-expressions"></a>

It is also possible to add expressions that chain different requirements. In this case do not forget to put brackets around individual parts of the expression such as:

```

```

### Save selected features as a new file <a id="save-selected-features-as-a-new-file"></a>

- `Layer-Properties` → `Export` → `Save only selected features`.

:::{dropdown} Example: Export selected features as a new file
:open:
<video width="90%" controls src="https://github.com/GIScience/gis-training-resource-center/raw/main/fig/en_qgis_select_export_wiki.mp4"></video>
:::



## Select by expression options <a id="select-by-expression-options"></a>

::::{tab-set}

:::{tab-item} Arithmetic operators
| operator | functionality          |
|----------|------------------------|
| __`+`__    | addition               |
| __`-`__    | subtraction           |
| __`*`__    | multiplication         |
| __`/`__    | division               |
| __`%`__    | remainder of division  |
:::

:::{tab-item} Comparison operators
| operator | functionality            |
|----------|--------------------------|
| __`=`__    | equals                   |
| __`!=`__   | not equal                |
| __`<`__    | less than                |
| __`>`__    | greater than             |
| __`<=`__   | less than or equal to    |
| __`>=`__   | greater than or equal to |
:::

:::{tab-item} Logical operators
Operators such as AND, OR can be used to combine different queries or criteria
| operator | functionality          |
|----------|------------------------|
| __`AND`__  | logical AND            |
| __`OR`__   | logical OR             |
| __`NOT`__  | logical NOT            |
:::

:::{tab-item} Special operators
| operator      | functionality                                  |
|---------------|------------------------------------------------|
| __`LIKE`__      | pattern matching                               |
| __`IN`__        | checks if a value is in a list of values       |
| __`IS NULL`__   | checks for null values                         |
| __`BETWEEN`__   | checks if a value is within a specified range  |
| __`CASE WHEN`__ | conditional expressions                        |
:::

::::

## Further resources <a id="further-resources"></a>

You can access information about logical operators in QGIS documentation through the [following link](https://docs.qgis.org/3.28/en/docs/user_manual/working_with_vector/attribute_table.html#selecting-features).