LEFT
Applies to: 
Calculated column
Calculated table
Measure
Visual calculation
Returns the specified number of characters from the start of a text string.
Syntax
LEFT(<text>, <num_chars>)
Parameters
| Term | Definition |
|---|---|
| text | The text string containing the characters you want to extract, or a reference to a column that contains text. |
| num_chars | (optional) The number of characters you want LEFT to extract; if omitted, 1. |
Return value
A text string.
Remarks
Whereas Microsoft Excel contains different functions for working with text in single-byte and double-byte character languages, DAX works with Unicode and stores all characters as the same length; therefore, a single function is enough.
This function is not supported for use in DirectQuery mode when used in calculated columns or row-level security (RLS) rules.
Example
The following example returns the first five characters of the company name in the column [ResellerName] and the first five letters of the geographical code in the column [GeographyKey] and concatenates them, to create an identifier.
= CONCATENATE(LEFT('Reseller'[ResellerName],LEFT(GeographyKey,3))
If the num_chars argument is a number that is larger than the number of characters available, the function returns the maximum characters available and does not raise an error. For example, the column [GeographyKey] contains numbers such as 1, 12 and 311; therefore the result also has variable length.