**Important**: This article can also be used to work with expressions in Vizlib Input Form.

**TABLE OF CONTENTS**

- Referencing Column/Field Values with Column() Syntax
- Best Practice - Referencing with a Column/Field Name
- Best Practice - Referencing with a Column/Field Number
- Expression Editor
- Use Variable in Calculation

### Referencing Column/Field Values with Column() Syntax

There are limitations on using column() syntax to refer to column values in **Vizlib Writeback Table** or field values in **Vizlib Input Form**. We've listed the cases where column() syntax can be used here.

- The
**Calculation**property for the**Calculated Column**data type. **Hide**and**Show**conditions, namely- The
**Show field if**property for**Vizlib****Input Form**fields. - Form
**Groups**,**Captions**and**Dividers**in**Vizlib Input Form**and**Vizlib Writeback Table**Form View.

- The
- Numeric inputs e.g.
**Column("Slider") / 100** **Validation Expression**property - Validation using Qlik Expression.

If you would like to add the value of two columns together you can use a **Calculation **like the example shown here.

Column("Slider")+Column("Numeric")

The calculation should give the result shown in **Figure 1**, where the **Calculated Column **displays the sum of the **Slider **and **Numeric **columns.

Figure 1: Calculated Column Result

### Best Practice - Referencing with a Column/Field Name

Double quotes, single quotes, square brackets, and no quotes can be used when referencing the column/field name in the **Column()** function. We recommend using double quotes because if you open the expression in the Qlik Expression Editor you will not get any syntax errors.

Column("Slider")

Other valid Column() syntax with Column/Field name.

Column('Slider'),Column([Slider]),Column(Slider)

### Best Practice - Referencing with a Column/Field Number

We do not recommend referencing values using the Column/Field number as differences between the columns listed in the expression and the property panel can develop over time if any columns are re-ordered. If you're using column/field numbers in expressions, you may find you need to

- change the expression to make sure your calculation works.
- use a reference with column/field name.

Column(1)

Columns/Fields are numbered in the order of their place in the property panel in the Writeback Table or Input Form starting from 1 for the top column/field.

- Writeback Table - Columns
- Input Form - Fields

### Expression Editor

You can open the expression editor by clicking on thebutton where it's displayed in the property panel. The expression editor is useful for complicated expression and you need some help with the expression syntax. **Figure 2** selects **Calculated Column**, scrolls to the **Type **section in the property panel, and opens the editor for the **Calculation **function.

Figure 2: Expression Editor

### Use Variable in Calculation

When you're working with calculated columns in **Vizlib Writeback Table** (and calculated fields in **Vizlib Input Form**) and using a **Calculation **that is stored in a variable, you want the Qlik Engine to evaluate the variable before it's used in the calculation in the table. In the **Type **settings for **Calculated Column** / **Calculated Field,** you can now enable the **Use Variable in Calculation** checkbox (**Figure 3**). This works for all **Evaluation Types**, *Simple *and *Qlik Expression*.

Figure 3: Use Variable in Calculation

**Use Variable in Calculation**is checked the expression in**Calculation**will be evaluated (the variable will be expanded) before it's evaluated again with column/field values from the table/form.**Use Variable in Calculation**is unchecked (the default setting) the**Calculation**property will be used without evaluating it before it's being used in the table/form.

If you select **Use Variable in Calculation** and the **Calculation** uses column syntax, you'll see a warning displayed (**Figure 4**). This is because when the Qlik Engine evaluates the **Calculation **before it's used in the table/form, it will evaluate as an error because Column syntax in the context of the property panel is not valid. Uncheck **Use Variable in Calculation** to solve the issue.

Figure 4: Calculation Warning