About Equations

This article provides a comprehensive guide on utilizing Equation fields in your Knack app.

What is an equation? 

Equation fields function by merging field values, numbers, and other mathematical functions to construct an equation that will be calculated for each record. These fields are a specific type of field found on a table within the Data section of the Builder.

There are two equation types available: Number and Date.

Numeric Equation example: (Sales - Expenses) * 12

Date Equation example: {Date Completed} - {Date Started}

 

Managing Equations

Adding an Equation

To add a field to a table in the Builder's Data section, start by selecting the desired table from the left menu. Next, click on the "Add Field" button located at the top of the page.

This will give you the option to choose the "Equation" field type from the left side of the screen:

After selecting the "Equation" field type, a popup will appear where you can customize the settings for your Equation field. Once you have configured the field, simply click on the "Add Field" button located at the bottom of the pop-up window.

 

Editing an Equation

To modify an existing Equation, choose the table that includes the Equation field and then select the additional options icon (represented by "...") located beside the field's name.

 

Deleting an Equation

To remove an Equation, navigate to the table that contains the Equation field and click on the additional options icon (represented by "...") next to the field's name. From the dropdown menu, select the "Delete" option.

 

Building an Equation

Equations can take many different forms. See the Equation Types section for details on these options.

To build to your equation: 

• Type the name of the field directly in the formula input box.
• Use the "Fields’"dropdown list to select any available fields, or
• Type numbers or mathematical operators directly into the input box.

Below the equation editor, the Example Output shows you an example output of the current formula:

Accessing Connected Fields

As with text formulas, equations give you the option of retrieving data from connected records. If you start typing the name of a field on a connected table, you'll see it appear among the suggestions with the format of "Field connected with Table > Connected Table."

Using Multiple Choice Fields in Equations

Multiple choice fields can be utilized in equations, whereby these values are automatically converted into numerical values for calculation purposes.

Non-numeric characters are automatically removed and the remaining value is considered for calculation. In case there is no number left, zero will be used as the default value.

Using Yes / No Fields in Equations

Yes/No fields can be utilized in equations. In these equations, the values of No and Yes are converted to numerical values, where No is represented as 0 and Yes is represented as 1, which are then used in the equation.

Using Equations on Live App Forms

Requirements:

1. All fields required for the equation must be included on the form. Similarly, if you are setting a value in a record rule using a formula field, that field must also be present on the form.
2. The equation must be a Numeric equation and cannot be a Date Type.
3. The equation cannot use other formulas (sum, count, etc.)

Equation fields can be incorporated into forms to create dynamic calculators that update in real-time. Let's take a look at a basic example:

 

Operators

You can use the following operators in your equations:

Operator	Meaning
+	adds
-	subtracts
*	multiples
/	divides
==	equals
!=	not equals
>	greater than
<	less than
>=	greater than or equal to
<=	less than or equal to
&	and
|	or

 

Order of Operations

If your equation field relies on other formulas or fields with conditional rules, it is important to arrange them in the correct order. Knack processes these fields in the order they are listed in the table under the "Fields" section.

In simpler terms, if an equation depends on a field, a field with a conditional rule, or another equation, make sure to list those fields above the equation that utilizes them.

 

Equation Types: Settings and Functions

Numeric Equations

Numeric equations are powerful tools that allow you to calculate field values, numbers, and perform various mathematical functions. Additionally, you have the flexibility to format your results in different number formats, including decimals, rounding, and currency.

To activate a numeric equation, simply select the "Equation Type" option and set it to "Numeric".

Numeric Equation Settings

There are numerous settings available for numeric equations. See full list of numeric equations settings here.

Numeric Equation Functions

Many regular math functions (such as "ceil" or "max") can be used in Knack numeric equations. Others, like "getDateDayOfMonth" provide numeric values for a date. Learn more here.

 

Date Equations

Date equations are capable of performing calculations involving dates and formatting the results in various units such as hours, days, weeks, and more. To enable a date equation, simply select the "Equation Type" option and set it to "Date".

Selecting the "Date" equation type reveals the "Date Type" and "Result Type" options.

 

Date Equation Settings

There are a variety of options available for date equations. See full list of date equations settings here.

Date Equation Functions

currentTime(): Returns the current Date and Time according to your App's Timezone settings.

getDateDayOfWeek(): Returns the numeric day of the week.

getDateDayOfMonth(): Returns the numeric day of the month.

getDateYear(): Returns the numeric year of the date. 

getDateWeek(): Returns the numeric week of the year.

Detailed Equation Examples

Conditional Equations

Your equation can accept conditional rules using the ternary operator. A ternary operation allows three operands and can be used as a shortcut for the if statement.

An example:

Condition ? Equation_1 : Equation_2

This means if your condition is true, Knack will use the equation or value followed by the "?" symbol. If your condition is false, Knack will use the second equation or value followed by the ":" symbol.

Note that you can nest ternary statements to have more than two conditions/results like so:

Condition A ? Result 1 : (Condition B ? Result 2 : Result 3)

Also, you can use an "&" symbol to represent AND and a "|" symbol to represent OR in an equation like so:

Condition A > 0 & Condition B > 10 ? Equation 1 : Equation 2

Conditional Example 1:

There may be times where you need to track total elapsed time. This could can easily be done using the currentTime() function, but what happens when your date field is blank?

A blank date would be interpreted as "0", which Knack would interpret as "January 1, 1970", resulting in a very large negative number. Using a conditional rule we can make sure our equation remains "0" instead:

{Invoice Date} > 0 ? {Invoice Date} - currentTime() : 0

Conditional Example 2:

This example shows how to apply an additional 3% late fee to a charge:

{Time of Payment} > {Due Date} ? {Cost} * 1.03 : {Cost}

Conditional Example 3:

To trigger an equation when values are equal you can use the "==" operator:

{Budget Period} == 1 ? {Q1 Date} : {Budget Period}==2 ? {Q2 Date} : 0

Conditional Example 4

This complex example uses the following logic:

• If Time of Payment is later than Due Date, charge an extra 3%

• If Time of Payment is earlier than the Due Date, charge 1% less

• Otherwise (if Time of Payment equals Due Date), charge the normal amount

{Time of Payment} > {Due Date} ? ({Cost} 1.03) : ({Time of Payment} < {Due Date} ? {Cost 0.99} : {Cost})

Conditional Example 5

This complex example uses the following logic:

• If Start Date is blank, then nothing should be calculated

• If End Date is blank, then calculate the difference between the current date and the Start Date

• If Start Date and End Date are both populated, then calculate the difference between the End Date and the Start Date

• Otherwise (if they're both blank), set the value to zero

{End Date} > 0 & {Start Date} > 0 ? {End Date} - {Start Date} : {Start Date} > 0 ? currentTime() - {Start Date} : 0

 

Conditional Equations with Text Fields

Conditional rules don’t currently work with text fields, but you can map your text fields to number fields and use the number fields to in your equation. Assuming you already have a short text field called "Text":

1. Add a number field (we’ll call it Num).

2. Add a conditional rule to the Num for each option you want to account for Text; e.g. set Num to 1 if Text is First Choice, set Num to 2 if Text is Second Choice, etc.

3. Run a batch update on your data (even on a new temporary field) to populate the Num field via its conditional rules.

4. Use "Num" in place of "Text" in your equations.

Conditional Equation With Text Fields Example

If we want the following conditions tested:

• If Text is First Choice, ie: Num is 1, set equation to 1

• If Text is Second Choice, ie: Num is 2 set equation to 2

• If Text is anything else, set equation to 0

In the equation, you would need to utilize the "Num" field since equations cannot use "Text" fields. Therefore, the equation would be structured as follows:

{Num} ==1 ? 1 : {Num} ==2 ? 2 : 0

 

Using Equations in Your App

Use Equations in Equation or Text Formula Fields

Just as in any other field on an table connected to another table, equations fields can be used in text formulas or in other equation fields.

Viewing Equations in the Builder

Equation values will display in the "Records" tab in a table in the Builder. Here you can view and reference these values, as well as using record filters to display particular values for this equation field.

Viewing Equations in the Live App

With the exception of Maps, Menu and Rich Text views, Equation fields can be added and used to display values in all page views.

 

How To Guides

• Calculate Age in Years from a Birthday
• How To Start an Auto Increment Field from Any Number

 

Troubleshooting 

Can't Access Connected Field

If you're unable to access a connected field in a formula, check the connection between the two tables. You can only access fields from a table with a many-to-one or one-to-one relationship with the table you're adding the equation field to.

For example, let's say that many Tasks can be connected to one Project, and there's a number field called Hourly Rate in the Project table.

You can create an equation in the Tasks table that pulls in the value from the Hourly Rate field in the Project's table, because there's only one hourly rate value to pull in.

However, if you had a number fields called Hours Worked in the Tasks table, you wouldn't be able to access that field in an equation in the Projects table. There would be multiple Hours Worked values to pull in and an equation field can't do that.

In a case like that, you could use a formula field to access all the connected Hours Worked values. Then, the formula field could be used in the equation.

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