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toscalar()
Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer ✅ Azure Monitor ✅ Microsoft Sentinel
Returns a scalar constant value of the evaluated expression.
This function is useful for queries that require staged calculations. For example, calculate a total count of events, and then use the result to filter groups that exceed a certain percent of all events.
Any two statements must be separated by a semicolon.
Syntax
toscalar(
expression)
Learn more about syntax conventions.
Parameters
Name | Type | Required | Description |
---|---|---|---|
expression | string |
✔️ | The value to convert to a scalar value. |
Returns
A scalar constant value of the evaluated expression. If the result is a tabular, then the first column and first row will be taken for conversion.
Tip
You can use a let statement for readability of the query when using toscalar()
.
Limitations
toscalar()
can't be applied on a scenario that applies the function on each row. This is because the function can only be calculated a constant number of times during the query execution.
Usually, when this limitation is hit, the following error will be returned: can't use '<column name>' as it is defined outside its row-context scope.
In the following example, the query fails with the error:
'toscalar': can't use 'x' as it is defined outside its row-context scope.
let _dataset1 = datatable(x:long)[1,2,3,4,5];
let _dataset2 = datatable(x:long, y:long) [ 1, 2, 3, 4, 5, 6];
let tg = (x_: long)
{
toscalar(_dataset2| where x == x_ | project y);
};
_dataset1
| extend y = tg(x)
This failure can be mitigated by using the join
operator, as in the following example:
let _dataset1 = datatable(x: long)[1, 2, 3, 4, 5];
let _dataset2 = datatable(x: long, y: long) [1, 2, 3, 4, 5, 6];
_dataset1
| join (_dataset2) on x
| project x, y
Output
x | y |
---|---|
1 | 2 |
3 | 4 |
5 | 6 |
Examples
Evaluate Start
, End
, and Step
as scalar constants, and use the result for range
evaluation.
let Start = toscalar(print x=1);
let End = toscalar(range x from 1 to 9 step 1 | count);
let Step = toscalar(2);
range z from Start to End step Step | extend start=Start, end=End, step=Step
Output
z | start | end | step |
---|---|---|---|
1 | 1 | 9 | 2 |
3 | 1 | 9 | 2 |
5 | 1 | 9 | 2 |
7 | 1 | 9 | 2 |
9 | 1 | 9 | 2 |
The following example shows how toscalar
can be used to "fix" an expression
so that it will be calculated precisely once. In this case, the expression being
calculated returns a different value per evaluation.
let g1 = toscalar(new_guid());
let g2 = new_guid();
range x from 1 to 2 step 1
| extend x=g1, y=g2
Output
x | y |
---|---|
e6a15e72-756d-4c93-93d3-fe85c18d19a3 | c2937642-0d30-4b98-a157-a6706e217620 |
e6a15e72-756d-4c93-93d3-fe85c18d19a3 | c6a48cb3-9f98-4670-bf5b-589d0e0dcaf5 |