diff --git a/bft/testers/velox/runner.py b/bft/testers/velox/runner.py
index 3483f3bb..fc7438fa 100644
--- a/bft/testers/velox/runner.py
+++ b/bft/testers/velox/runner.py
@@ -5,7 +5,7 @@
 
 
 def is_type_supported(type):
-    return type in set({"i64", "fp64", "boolean"})
+    return type in set({"i64", "fp64", "boolean", "string"})
 
 
 class VeloxRunner(SqlCaseRunner):
diff --git a/cases/string/substring.yaml b/cases/string/substring.yaml
index a4b2253b..51b56d6a 100644
--- a/cases/string/substring.yaml
+++ b/cases/string/substring.yaml
@@ -13,6 +13,17 @@ cases:
     result:
       value: 'abcde'
       type: string
+  - group: basic
+    args:
+      - value: 'abcdefg'
+        type: string
+      - value: 1
+        type: i64
+      - value: 5
+        type: i64
+    result:
+      value: 'abcde'
+      type: string
   - group:
       id: negative_start
       description: Example where start argument is a negative integer
@@ -26,6 +37,17 @@ cases:
     result:
       value: 'ef'
       type: string
+  - group: negative_start
+    args:
+      - value: 'abcdefg'
+        type: string
+      - value: -3
+        type: i64
+      - value: 2
+        type: i64
+    result:
+      value: 'ef'
+      type: string
   - group:
       id: start_greater_than_length
       description: Example where start argument greater than the length of the string
@@ -39,6 +61,17 @@ cases:
     result:
       value: ''
       type: string
+  - group: start_greater_than_length
+    args:
+      - value: 'abcdefg'
+        type: string
+      - value: 10
+        type: i64
+      - value: 2
+        type: i64
+    result:
+      value: ''
+      type: string
   - group:
       id: multi_byte_characters
       description: Example where multi byte characters exist in the string
@@ -52,3 +85,14 @@ cases:
     result:
       value: '😊a😊'
       type: string
+  - group: multi_byte_characters
+    args:
+      - value: '😊a😊b😊😊'
+        type: string
+      - value: 1
+        type: i64
+      - value: 3
+        type: i64
+    result:
+      value: '😊a😊'
+      type: string
diff --git a/dialects/postgres.yaml b/dialects/postgres.yaml
index 319a6f9b..e82d5867 100644
--- a/dialects/postgres.yaml
+++ b/dialects/postgres.yaml
@@ -219,6 +219,12 @@ scalar_functions:
           - i32
         result: fp64
   - name: substring
+    unsupported_kernels:
+      - args:
+          - string
+          - i64
+          - i64
+        result: string
   - name: concat
     local_name: "||"
     infix: True
diff --git a/dialects/velox_presto.yaml b/dialects/velox_presto.yaml
index f761da69..4eee9344 100644
--- a/dialects/velox_presto.yaml
+++ b/dialects/velox_presto.yaml
@@ -287,5 +287,11 @@ scalar_functions:
         result: fp64
   - name: substring
     local_name: substr
+    unsupported_kernels:
+      - args:
+          - string
+          - i32
+          - i32
+        result: string
   - name: concat
   - name: like