diff --git a/src/data/compare.rs b/src/data/compare.rs
index 8d117fbe..b9a8991d 100644
--- a/src/data/compare.rs
+++ b/src/data/compare.rs
@@ -24,7 +24,7 @@ macro_rules! return_if_resolved {
 }
 
 #[inline]
-fn compare_key(a: &[u8], b: &[u8]) -> Ordering {
+pub(crate) fn compare_key(a: &[u8], b: &[u8]) -> Ordering {
     use StorageTag::*;
 
     return_if_resolved!(a[0].cmp(&b[0]));
diff --git a/src/transact/triple.rs b/src/transact/triple.rs
index 34ad39c0..167764f2 100644
--- a/src/transact/triple.rs
+++ b/src/transact/triple.rs
@@ -1,5 +1,5 @@
 use crate::data::attr::{Attribute, AttributeTyping};
-use crate::data::compare::rusty_cmp;
+use crate::data::compare::{compare_key, rusty_cmp};
 use crate::data::encode::{
     decode_ae_key, decode_ea_key, decode_vae_key, decode_value, decode_value_from_key,
     decode_value_from_val, encode_aev_key, encode_ave_key, encode_ave_key_for_unique_v,
@@ -193,44 +193,34 @@ impl SessionTx {
             let ave_encoded = encode_ave_key(attr.id, v, e_in_key, vld_in_key);
             // checking of unique constraints
             if attr.indexing.is_unique_index() {
-                let current_ave_encoded = if attr.with_history {
-                    ave_encoded.clone()
+                let (current_ave_encoded, vld_in_key) = if attr.with_history {
+                    (ave_encoded.clone(), vld)
                 } else {
-                    encode_ave_key(attr.id, v, e_in_key, Validity::NO_HISTORY)
+                    (
+                        encode_ave_key(attr.id, v, e_in_key, Validity::NO_HISTORY),
+                        Validity::NO_HISTORY,
+                    )
                 };
                 // back scan
                 if attr.with_history {
-                    let ave_encoded_upper_bound =
-                        encode_ave_key(attr.id, v, e_in_key, Validity::MIN);
-                    if let Some((k_slice, v_slice)) = self
-                        .bounded_scan_first(&current_ave_encoded, &ave_encoded_upper_bound)
-                        .pair()?
-                    {
-                        let (_found_aid, found_eid, _found_vld) = decode_ae_key(k_slice)?;
-                        let found_op = StoreOp::try_from(v_slice[0])?;
-                        let found_v = decode_value_from_key(k_slice)?;
-                        if found_eid != eid && found_op.is_assert() {
+                    for item in self.triple_av_before_scan(attr.id, v, vld_in_key) {
+                        let (_, _, found_eid) = item?;
+                        if found_eid != eid {
                             return Err(TripleError::UniqueConstraintViolated(
                                 attr.keyword.clone(),
-                                format!("back scan found: {:?} vs {:?}", v, found_v),
+                                format!("{:?}", v),
                             )
                             .into());
                         }
                     }
                 }
 
-                let ave_encoded_lower_bound = encode_ave_key(attr.id, v, e_in_key, Validity::MAX);
-                if let Some((k_slice, v_slice)) = self
-                    .bounded_scan_last(&ave_encoded_lower_bound, &current_ave_encoded)
-                    .pair()?
-                {
-                    let (_found_aid, found_eid, _found_vld) = decode_ae_key(k_slice)?;
-                    let found_op = StoreOp::try_from(v_slice[0])?;
-                    let found_v = decode_value_from_key(k_slice)?;
-                    if found_eid != eid && found_op.is_assert() {
+                for item in self.triple_av_after_scan(attr.id, v, vld_in_key) {
+                    let (_, _, found_eid) = item?;
+                    if found_eid != eid {
                         return Err(TripleError::UniqueConstraintViolated(
                             attr.keyword.clone(),
-                            format!("forward scan found: {:?} vs {:?}", v, found_v),
+                            format!("{:?}", v),
                         )
                         .into());
                     }
@@ -475,6 +465,16 @@ impl SessionTx {
         let upper = encode_ave_key(aid, v, EntityId::MAX_PERM, Validity::MIN);
         TripleAttrValueBeforeIter::new(self.tx.iterator(), lower, upper, before)
     }
+    pub(crate) fn triple_av_after_scan(
+        &mut self,
+        aid: AttrId,
+        v: &Value,
+        after: Validity,
+    ) -> impl Iterator<Item = Result<(AttrId, StaticValue, EntityId)>> {
+        let lower = encode_ave_key(aid, v, EntityId::MIN_PERM, Validity::MAX);
+        let upper = encode_ave_key(aid, v, EntityId::MAX_PERM, Validity::MIN);
+        TripleAttrValueAfterIter::new(self.tx.iterator(), lower, upper, after)
+    }
     pub(crate) fn triple_vref_a_scan(
         &mut self,
         v_eid: EntityId,
@@ -883,6 +883,65 @@ impl Iterator for TripleAttrValueBeforeIter {
     }
 }
 
+// after version
+
+struct TripleAttrValueAfterIter {
+    it: DbIter,
+    lower_bound: EncodedVec<LARGE_VEC_SIZE>,
+    current: EncodedVec<LARGE_VEC_SIZE>,
+    after: Validity,
+}
+
+impl TripleAttrValueAfterIter {
+    fn new(
+        builder: IterBuilder,
+        lower_bound: EncodedVec<LARGE_VEC_SIZE>,
+        upper_bound: EncodedVec<LARGE_VEC_SIZE>,
+        after: Validity,
+    ) -> Self {
+        let it = builder.lower_bound(&lower_bound).start();
+        Self {
+            it,
+            lower_bound,
+            current: upper_bound,
+            after,
+        }
+    }
+    fn next_inner(&mut self) -> Result<Option<(AttrId, StaticValue, EntityId)>> {
+        loop {
+            self.it.seek_back(&self.current);
+            match self.it.pair()? {
+                None => return Ok(None),
+                Some((k_slice, v_slice)) => {
+                    if compare_key(k_slice, &self.lower_bound) == std::cmp::Ordering::Less {
+                        return Ok(None);
+                    }
+                    let (aid, eid, tid) = decode_ae_key(k_slice)?;
+                    if tid < self.after {
+                        self.current.encoded_entity_amend_validity(self.after);
+                        continue;
+                    }
+                    let v = decode_value_from_key(k_slice)?;
+                    self.current.copy_from_slice(k_slice);
+                    self.current.encoded_entity_amend_validity_to_last();
+                    let op = StoreOp::try_from(v_slice[0])?;
+                    if op.is_assert() {
+                        return Ok(Some((aid, v.to_static(), eid)));
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl Iterator for TripleAttrValueAfterIter {
+    type Item = Result<(AttrId, StaticValue, EntityId)>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        swap_option_result(self.next_inner())
+    }
+}
+
 // normal version
 
 struct TripleValueRefAttrIter {