diff --git a/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs b/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs
index d41c79b30..f0d2d0b7e 100644
--- a/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs
+++ b/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs
@@ -1,6 +1,7 @@
 use crate::db::clickhouse::migration_manager::migration_trait::Migration;
 use crate::db::clickhouse::ClickHouseConnectionInfo;
 use crate::error::{Error, ErrorDetails};
+use crate::result::ResultExt;
 use async_trait::async_trait;
 
 pub struct Migration0041<'a> {
@@ -10,22 +11,54 @@ pub struct Migration0041<'a> {
 #[async_trait]
 impl Migration for Migration0041<'_> {
     async fn can_apply(&self) -> Result<(), Error> {
         Ok(())
     }
 
     async fn should_apply(&self) -> Result<bool, Error> {
-        let query =
-            "SELECT 1 FROM system.functions WHERE name = 'tensorzero_uint_to_uuid'".to_string();
-        let result = self
-            .clickhouse
-            .run_query_synchronous_no_params(query)
-            .await?;
-        if result.response.contains('1') {
-            return Ok(false);
-        }
-        if result.response.trim().is_empty() || result.response.contains("0") {
-            return Ok(true);
-        }
-        Err(Error::new(ErrorDetails::ClickHouseMigration {
-            id: "0041".to_string(),
-            message: format!(
-                "Unexpected response when checking for tensorzero_uint_to_uuid function: {}",
-                result.response.trim()
-            ),
-        }))
+        // Check if the SQL UDF already exists. On ClickHouse, SQL UDFs are exposed via
+        // `system.sql_functions` (not `system.functions`). Fall back to `system.functions`
+        // defensively in case of version differences.
+        async fn function_exists(clickhouse: &ClickHouseConnectionInfo) -> Result<bool, Error> {
+            // Prefer system.sql_functions if available
+            let sql_fn_check = "SELECT 1 FROM system.sql_functions WHERE name = 'tensorzero_uint_to_uuid'";
+            match clickhouse
+                .run_query_synchronous_no_params(sql_fn_check.to_string())
+                .await
+            {
+                Ok(res) => {
+                    if !res.response.trim().is_empty() && res.response.contains('1') {
+                        return Ok(true);
+                    }
+                }
+                // If the system table doesn't exist on this server, ignore and try the fallback.
+                Err(_e) => {}
+            }
+
+            // Fallback: some builds expose user-defined SQL functions under system.functions as well.
+            let fallback_check =
+                "SELECT 1 FROM system.functions WHERE name = 'tensorzero_uint_to_uuid'";
+            let res = clickhouse
+                .run_query_synchronous_no_params(fallback_check.to_string())
+                .await?;
+            Ok(!res.response.trim().is_empty() && res.response.contains('1'))
+        }
+
+        let exists = function_exists(self.clickhouse).await?;
+        Ok(!exists)
     }
 
     async fn apply(&self, _clean_start: bool) -> Result<(), Error> {
         let on_cluster_name = self.clickhouse.get_on_cluster_name();
         let query = format!(
             r"CREATE FUNCTION IF NOT EXISTS tensorzero_uint_to_uuid{on_cluster_name} AS (x) -> reinterpretAsUUID(
             concat(
                 substring(reinterpretAsString(x), 9, 8),
                 substring(reinterpretAsString(x), 1, 8)
             )
         );",
         );
         self.clickhouse
             .run_query_synchronous_no_params(query)
             .await?;
 
         Ok(())
     }
 
     fn rollback_instructions(&self) -> String {
         "DROP FUNCTION IF EXISTS tensorzero_uint_to_uuid;".to_string()
     }
 
     async fn has_succeeded(&self) -> Result<bool, Error> {
-        let should_apply = self.should_apply().await?;
-        Ok(!should_apply)
+        // Reuse the existence logic from should_apply: if we should not apply anymore,
+        // then the migration has succeeded.
+        let should_apply = self.should_apply().await?;
+        Ok(!should_apply)
     }
 }

diff --git a/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs b/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs
index d41c79b30..10f36e579 100644
--- a/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs
+++ b/tensorzero-core/src/db/clickhouse/migration_manager/migrations/migration_0041.rs
@@ -1,63 +1,83 @@
 use crate::db::clickhouse::migration_manager::migration_trait::Migration;
 use crate::db::clickhouse::ClickHouseConnectionInfo;
 use crate::error::{Error, ErrorDetails};
 use async_trait::async_trait;
 
 pub struct Migration0041<'a> {
     pub clickhouse: &'a ClickHouseConnectionInfo,
 }
 
 #[async_trait]
 impl Migration for Migration0041<'_> {
     async fn can_apply(&self) -> Result<(), Error> {
         Ok(())
     }
 
     async fn should_apply(&self) -> Result<bool, Error> {
-        let query =
-            "SELECT 1 FROM system.functions WHERE name = 'tensorzero_uint_to_uuid'".to_string();
-        let result = self
-            .clickhouse
-            .run_query_synchronous_no_params(query)
-            .await?;
-        if result.response.contains('1') {
-            return Ok(false);
-        }
-        if result.response.trim().is_empty() || result.response.contains("0") {
-            return Ok(true);
-        }
-        Err(Error::new(ErrorDetails::ClickHouseMigration {
-            id: "0041".to_string(),
-            message: format!(
-                "Unexpected response when checking for tensorzero_uint_to_uuid function: {}",
-                result.response.trim()
-            ),
-        }))
+        // Deterministically check if the function exists by returning a row only when it does.
+        // If no row is returned, we should apply the migration.
+        let query = r"
+            SELECT 1 AS exists
+            WHERE EXISTS(
+                SELECT 1 FROM system.functions WHERE name = 'tensorzero_uint_to_uuid'
+            )
+            FORMAT JSONEachRow
+        "
+        .to_string();
+        let result = self.clickhouse.run_query_synchronous_no_params(query).await?;
+        Ok(result.response.trim().is_empty())
     }
 
     async fn apply(&self, _clean_start: bool) -> Result<(), Error> {
         let on_cluster_name = self.clickhouse.get_on_cluster_name();
         let query = format!(
             r"CREATE FUNCTION IF NOT EXISTS tensorzero_uint_to_uuid{on_cluster_name} AS (x) -> reinterpretAsUUID(
-            concat(
-                substring(reinterpretAsString(x), 9, 8),
-                substring(reinterpretAsString(x), 1, 8)
-            )
-        );",
+                toFixedString(
+                    concat(
+                        substring(reinterpretAsString(x), 9, 8),
+                        substring(reinterpretAsString(x), 1, 8)
+                    ),
+                    16
+                )
+            );",
         );
         self.clickhouse
             .run_query_synchronous_no_params(query)
             .await?;
 
         Ok(())
     }
 
     fn rollback_instructions(&self) -> String {
         "DROP FUNCTION IF EXISTS tensorzero_uint_to_uuid;".to_string()
     }
 
     async fn has_succeeded(&self) -> Result<bool, Error> {
-        let should_apply = self.should_apply().await?;
-        Ok(!should_apply)
+        // Succeeded if the function now exists (i.e., the query returns a row).
+        let query = r"
+            SELECT 1 AS exists
+            WHERE EXISTS(
+                SELECT 1 FROM system.functions WHERE name = 'tensorzero_uint_to_uuid'
+            )
+            FORMAT JSONEachRow
+        "
+        .to_string();
+        let result = self.clickhouse.run_query_synchronous_no_params(query).await?;
+        Ok(!result.response.trim().is_empty())
     }
 }