Kusto - get all table row count

if you want to list the rows and tables in your Log Analytics workspace, here is a command to do so

union withsource = __TableName *
| summarize RowCount = count() by __TableName
| order by RowCount desc

If you want to search for xxxxxx inside all of your tables and count the rows it appears in

let something = "xxxxxx";
search *
| where * contains something
| summarize count() by $table

Later you can drill down even more. If you want to search for this something inside a particular table

let something = "xxxxxx";
AzureActivity
| where * contains something