Daily DAX : Day 451 ISSTRING

Power BI DAX Function: ISSTRING

The ISSTRING function in DAX checks whether a given value is of text (string) data type. It returns TRUE if the value is text, and FALSE otherwise.

Note: ISSTRING is an alias for the ISTEXT function. Both functions behave identically.

Syntax

ISSTRING(<value>)

Parameters

Parameter	Description
<value>	The value or expression to check (can be a column reference, scalar value, etc.).

Return Value

BOOLEAN: TRUE if the value is text/string, FALSE otherwise (including numbers, dates, blanks, etc.).

Example

EVALUATE
{
    ("Hello", ISSTRING("Hello")),        // Returns TRUE
    (123,    ISSTRING(123)),             // Returns FALSE
    (DATE(2026,1,1), ISSTRING(DATE(2026,1,1))),  // Returns FALSE
    (BLANK(), ISSTRING(BLANK()))         // Returns FALSE
}
    

Use Cases

• Data validation: Check if values in a column are actually text before performing string operations (e.g., concatenation, searching).
• Conditional logic: Apply different calculations based on data type, such as handling mixed-type columns safely.
• Error prevention: Avoid errors from functions like LEFT, SEARCH, or CONCATENATE when applied to non-text values.
• Dynamic measures/columns: Combine with IF to provide fallback values or messages when data is not text.

Sample Use Case in a Calculated Column

Safe Upper Case = 
IF(
    ISSTRING(Table[Column1]),
    UPPER(Table[Column1]),
    "Not Text"
)
    

This ensures UPPER is only applied to text values, returning a message otherwise.