diff --git a/cozo-core/src/data/program.rs b/cozo-core/src/data/program.rs
index 4e64bc6d..08e47eb2 100644
--- a/cozo-core/src/data/program.rs
+++ b/cozo-core/src/data/program.rs
@@ -183,6 +183,10 @@ impl TempSymbGen {
         self.last_id += 1;
         Symbol::new(&format!("*{}", self.last_id) as &str, span)
     }
+    pub(crate) fn next_ignored(&mut self, span: SourceSpan) -> Symbol {
+        self.last_id += 1;
+        Symbol::new(&format!("~{}", self.last_id) as &str, span)
+    }
 }
 
 #[derive(Debug, Clone)]
diff --git a/cozo-core/src/data/symb.rs b/cozo-core/src/data/symb.rs
index 22718ca3..b12206d6 100644
--- a/cozo-core/src/data/symb.rs
+++ b/cozo-core/src/data/symb.rs
@@ -87,6 +87,9 @@ impl Symbol {
     pub(crate) fn is_ignored_symbol(&self) -> bool {
         self.name == "_"
     }
+    pub(crate) fn is_generated_ignored_symbol(&self) -> bool {
+        self.name.starts_with('~')
+    }
     pub(crate) fn ensure_valid_field(&self) -> Result<()> {
         if self.name.contains('(') || self.name.contains(')') {
             #[derive(Debug, Error, Diagnostic)]
diff --git a/cozo-core/src/query/compile.rs b/cozo-core/src/query/compile.rs
index 69dcb4cc..a3042b98 100644
--- a/cozo-core/src/query/compile.rs
+++ b/cozo-core/src/query/compile.rs
@@ -95,6 +95,13 @@ struct RuleNotFound(String, #[label] SourceSpan);
 #[diagnostic(help("Required arity: {1}, number of arguments given: {2}"))]
 struct ArityMismatch(String, usize, usize, #[label] SourceSpan);
 
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub(crate) enum IndexPositionUse {
+    Join,
+    BindForLater,
+    Ignored,
+}
+
 impl<'a> SessionTx<'a> {
     pub(crate) fn stratified_magic_compile(
         &mut self,
@@ -221,26 +228,126 @@ impl<'a> SessionTx<'a> {
                             rel_app.span
                         )
                     );
+                    // already existing vars
                     let mut prev_joiner_vars = vec![];
+                    // vars introduced by right and joined
                     let mut right_joiner_vars = vec![];
+                    // used to split in case we need to join again
+                    let mut right_joiner_vars_pos = vec![];
+                    // vars introduced by right, regardless of joining
                     let mut right_vars = vec![];
+                    // used for choosing indices
+                    let mut join_indices = vec![];
 
-                    for var in &rel_app.args {
+                    for (i, var) in rel_app.args.iter().enumerate() {
                         if seen_variables.contains(var) {
                             prev_joiner_vars.push(var.clone());
                             let rk = gen_symb(var.span);
                             right_vars.push(rk.clone());
                             right_joiner_vars.push(rk);
+                            right_joiner_vars_pos.push(i);
+                            join_indices.push(IndexPositionUse::Join)
                         } else {
                             seen_variables.insert(var.clone());
                             right_vars.push(var.clone());
+                            if var.is_generated_ignored_symbol() {
+                                join_indices.push(IndexPositionUse::Ignored)
+                            } else {
+                                join_indices.push(IndexPositionUse::BindForLater)
+                            }
                         }
                     }
 
-                    let right =
-                        RelAlgebra::relation(right_vars, store, rel_app.span, rel_app.valid_at)?;
-                    debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
-                    ret = ret.join(right, prev_joiner_vars, right_joiner_vars, rel_app.span);
+                    let chosen_index =
+                        store.choose_index(&join_indices, rel_app.valid_at.is_some());
+
+                    match chosen_index {
+                        None => {
+                            // scan original relation
+                            let right = RelAlgebra::relation(
+                                right_vars,
+                                store,
+                                rel_app.span,
+                                rel_app.valid_at,
+                            )?;
+                            debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
+                            ret =
+                                ret.join(right, prev_joiner_vars, right_joiner_vars, rel_app.span);
+                        }
+                        Some((chosen_index, mapper, false)) => {
+                            // index-only
+                            let new_right_vars = mapper
+                                .into_iter()
+                                .map(|i| right_vars[i].clone())
+                                .collect_vec();
+                            let right = RelAlgebra::relation(
+                                new_right_vars,
+                                chosen_index,
+                                rel_app.span,
+                                rel_app.valid_at,
+                            )?;
+                            debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
+                            ret =
+                                ret.join(right, prev_joiner_vars, right_joiner_vars, rel_app.span);
+                        }
+                        Some((chosen_index, mapper, true)) => {
+                            // index-with-join
+                            let mut prev_joiner_first_vars = vec![];
+                            let mut middle_joiner_left_vars = vec![];
+                            let mut middle_vars = vec![];
+                            for i in mapper.iter() {
+                                let tv = gen_symb(right_vars[*i].span);
+                                if let Some(j) = right_joiner_vars_pos.iter().position(|el| el == i)
+                                {
+                                    prev_joiner_first_vars.push(prev_joiner_vars[j].clone());
+                                    middle_joiner_left_vars.push(tv.clone());
+                                }
+                                middle_vars.push(tv);
+                            }
+                            let middle_joiner_right_vars = mapper
+                                .iter()
+                                .enumerate()
+                                .filter_map(|(idx, orig_idx)| {
+                                    if *orig_idx < store.metadata.keys.len() {
+                                        Some(middle_vars[idx].clone())
+                                    } else {
+                                        None
+                                    }
+                                })
+                                .collect_vec();
+
+                            let final_joiner_vars = right_vars
+                                .iter()
+                                .take(store.metadata.keys.len())
+                                .cloned()
+                                .collect_vec();
+
+                            let middle = RelAlgebra::relation(
+                                middle_vars,
+                                chosen_index,
+                                rel_app.span,
+                                rel_app.valid_at,
+                            )?;
+                            ret = ret.join(
+                                middle,
+                                prev_joiner_first_vars,
+                                middle_joiner_left_vars,
+                                rel_app.span,
+                            );
+                            let final_alg = RelAlgebra::relation(
+                                right_vars,
+                                store,
+                                rel_app.span,
+                                rel_app.valid_at,
+                            )?;
+                            ret = ret.join(
+                                final_alg,
+                                middle_joiner_right_vars,
+                                final_joiner_vars,
+                                rel_app.span,
+                            );
+                        }
+                    }
                 }
                 MagicAtom::NegatedRule(rule_app) => {
                     let store_arity = store_arities.get(&rule_app.name).ok_or_else(|| {
@@ -279,46 +386,88 @@ impl<'a> SessionTx<'a> {
                     debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
                     ret = ret.neg_join(right, prev_joiner_vars, right_joiner_vars, rule_app.span);
                 }
-                MagicAtom::NegatedRelation(relation_app) => {
-                    let store = self.get_relation(&relation_app.name, false)?;
+                MagicAtom::NegatedRelation(rel_app) => {
+                    let store = self.get_relation(&rel_app.name, false)?;
                     ensure!(
-                        store.arity() == relation_app.args.len(),
+                        store.arity() == rel_app.args.len(),
                         ArityMismatch(
-                            relation_app.name.to_string(),
+                            rel_app.name.to_string(),
                             store.arity(),
-                            relation_app.args.len(),
-                            relation_app.span
+                            rel_app.args.len(),
+                            rel_app.span
                         )
                     );
 
+                    // already existing vars
                     let mut prev_joiner_vars = vec![];
+                    // vars introduced by right and joined
                     let mut right_joiner_vars = vec![];
+                    // used to split in case we need to join again
+                    let mut right_joiner_vars_pos = vec![];
+                    // vars introduced by right, regardless of joining
                     let mut right_vars = vec![];
+                    // used for choosing indices
+                    let mut join_indices = vec![];
 
-                    for var in &relation_app.args {
+                    for (i, var) in rel_app.args.iter().enumerate() {
                         if seen_variables.contains(var) {
                             prev_joiner_vars.push(var.clone());
                             let rk = gen_symb(var.span);
                             right_vars.push(rk.clone());
                             right_joiner_vars.push(rk);
+                            right_joiner_vars_pos.push(i);
+                            join_indices.push(IndexPositionUse::Join)
                         } else {
+                            seen_variables.insert(var.clone());
                             right_vars.push(var.clone());
+                            if var.is_generated_ignored_symbol() {
+                                join_indices.push(IndexPositionUse::Ignored)
+                            } else {
+                                join_indices.push(IndexPositionUse::BindForLater)
+                            }
                         }
                     }
 
-                    let right = RelAlgebra::relation(
-                        right_vars,
-                        store,
-                        relation_app.span,
-                        relation_app.valid_at,
-                    )?;
-                    debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
-                    ret = ret.neg_join(
-                        right,
-                        prev_joiner_vars,
-                        right_joiner_vars,
-                        relation_app.span,
-                    );
+                    let chosen_index =
+                        store.choose_index(&join_indices, rel_app.valid_at.is_some());
+
+                    match chosen_index {
+                        None | Some((_, _, true)) => {
+                            let right = RelAlgebra::relation(
+                                right_vars,
+                                store,
+                                rel_app.span,
+                                rel_app.valid_at,
+                            )?;
+                            debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
+                            ret = ret.neg_join(
+                                right,
+                                prev_joiner_vars,
+                                right_joiner_vars,
+                                rel_app.span,
+                            );
+                        }
+                        Some((chosen_index, mapper, false)) => {
+                            // index-only
+                            let new_right_vars = mapper
+                                .into_iter()
+                                .map(|i| right_vars[i].clone())
+                                .collect_vec();
+                            let right = RelAlgebra::relation(
+                                new_right_vars,
+                                chosen_index,
+                                rel_app.span,
+                                rel_app.valid_at,
+                            )?;
+                            debug_assert_eq!(prev_joiner_vars.len(), right_joiner_vars.len());
+                            ret = ret.neg_join(
+                                right,
+                                prev_joiner_vars,
+                                right_joiner_vars,
+                                rel_app.span,
+                            );
+                        }
+                    }
                 }
                 MagicAtom::Predicate(p) => {
                     ret = ret.filter(p.clone());
diff --git a/cozo-core/src/query/logical.rs b/cozo-core/src/query/logical.rs
index 6802ecc1..a1fdd8dd 100644
--- a/cozo-core/src/query/logical.rs
+++ b/cozo-core/src/query/logical.rs
@@ -163,7 +163,7 @@ impl InputAtom {
             .chain(stored.metadata.non_keys.iter())
         {
             let arg = args.remove(&col_def.name).unwrap_or_else(|| Expr::Binding {
-                var: gen.next(span),
+                var: gen.next_ignored(span),
                 tuple_pos: None,
             });
             new_args.push(arg)
@@ -238,7 +238,7 @@ impl InputRuleApplyAtom {
             match arg {
                 Expr::Binding { var, .. } => {
                     if var.is_ignored_symbol() {
-                        let dup = gen.next(var.span);
+                        let dup = gen.next_ignored(var.span);
                         args.push(dup);
                     } else if seen_variables.insert(var.clone()) {
                         args.push(var);
@@ -298,7 +298,7 @@ impl InputRelationApplyAtom {
             match arg {
                 Expr::Binding { var, .. } => {
                     if var.is_ignored_symbol() {
-                        args.push(gen.next(var.span));
+                        args.push(gen.next_ignored(var.span));
                     } else if seen_variables.insert(var.clone()) {
                         args.push(var);
                     } else {
diff --git a/cozo-core/src/query/stored.rs b/cozo-core/src/query/stored.rs
index 1ffe373d..20ff89af 100644
--- a/cozo-core/src/query/stored.rs
+++ b/cozo-core/src/query/stored.rs
@@ -18,16 +18,18 @@ use crate::data::expr::Expr;
 use crate::data::program::{FixedRuleApply, InputInlineRulesOrFixed, InputProgram, RelationOp};
 use crate::data::relation::{ColumnDef, NullableColType};
 use crate::data::symb::Symbol;
-use crate::data::tuple::{Tuple, ENCODED_KEY_MIN_LEN};
+use crate::data::tuple::Tuple;
 use crate::data::value::{DataValue, ValidityTs};
 use crate::fixed_rule::utilities::constant::Constant;
 use crate::fixed_rule::FixedRuleHandle;
 use crate::parse::parse_script;
 use crate::runtime::db::{CallbackCollector, CallbackOp};
-use crate::runtime::relation::{AccessLevel, extend_tuple_from_v, InputRelationHandle, InsufficientAccessLevel};
+use crate::runtime::relation::{
+    extend_tuple_from_v, AccessLevel, InputRelationHandle, InsufficientAccessLevel,
+};
 use crate::runtime::transact::SessionTx;
 use crate::storage::Storage;
-use crate::{Db, decode_tuple_from_kv, NamedRows, StoreTx};
+use crate::{Db, NamedRows, StoreTx};
 
 #[derive(Debug, Error, Diagnostic)]
 #[error("attempting to write into relation {0} of arity {1} with data of arity {2}")]
@@ -56,7 +58,6 @@ impl<'a> SessionTx<'a> {
                 #[diagnostic(code(eval::replace_in_trigger))]
                 struct ReplaceInTrigger(String);
                 bail!(ReplaceInTrigger(meta.name.to_string()))
-
             }
             if let Ok(old_handle) = self.get_relation(&meta.name, true) {
                 if !old_handle.indices.is_empty() {
@@ -82,7 +83,14 @@ impl<'a> SessionTx<'a> {
                             .get_single_program()?;
 
                     let (_, cleanups) = db
-                        .run_query(self, program, cur_vld, callback_targets, callback_collector, false)
+                        .run_query(
+                            self,
+                            program,
+                            cur_vld,
+                            callback_targets,
+                            callback_collector,
+                            false,
+                        )
                         .map_err(|err| {
                             if err.source_code().is_some() {
                                 err
@@ -194,9 +202,13 @@ impl<'a> SessionTx<'a> {
 
                     if propagate_triggers {
                         for trigger in &relation_store.rm_triggers {
-                            let mut program =
-                                parse_script(trigger, &Default::default(), &db.algorithms, cur_vld)?
-                                    .get_single_program()?;
+                            let mut program = parse_script(
+                                trigger,
+                                &Default::default(),
+                                &db.algorithms,
+                                cur_vld,
+                            )?
+                            .get_single_program()?;
 
                             make_const_rule(
                                 &mut program,
@@ -213,7 +225,14 @@ impl<'a> SessionTx<'a> {
                             );
 
                             let (_, cleanups) = db
-                                .run_query(self, program, cur_vld, callback_targets, callback_collector, false)
+                                .run_query(
+                                    self,
+                                    program,
+                                    cur_vld,
+                                    callback_targets,
+                                    callback_collector,
+                                    false,
+                                )
                                 .map_err(|err| {
                                     if err.source_code().is_some() {
                                         err
@@ -402,29 +421,24 @@ impl<'a> SessionTx<'a> {
                             if !existing.is_empty() {
                                 extend_tuple_from_v(&mut tup, &existing);
                             }
-                            if has_indices {
-                                if extracted != tup {
-                                    for (idx_rel, extractor) in relation_store.indices.values() {
-                                        let idx_tup_old =
-                                            extractor.iter().map(|i| tup[*i].clone()).collect_vec();
-                                        let encoded_old = idx_rel.encode_key_for_store(
-                                            &idx_tup_old,
-                                            Default::default(),
-                                        )?;
-                                        self.store_tx.del(&encoded_old)?;
-
-                                        let idx_tup_new = extractor
-                                            .iter()
-                                            .map(|i| extracted[*i].clone())
-                                            .collect_vec();
-                                        let encoded_new = idx_rel.encode_key_for_store(
-                                            &idx_tup_new,
-                                            Default::default(),
-                                        )?;
-                                        self.store_tx.put(&encoded_new, &[])?;
-                                    }
+                            if has_indices && extracted != tup {
+                                for (idx_rel, extractor) in relation_store.indices.values() {
+                                    let idx_tup_old =
+                                        extractor.iter().map(|i| tup[*i].clone()).collect_vec();
+                                    let encoded_old = idx_rel
+                                        .encode_key_for_store(&idx_tup_old, Default::default())?;
+                                    self.store_tx.del(&encoded_old)?;
+
+                                    let idx_tup_new = extractor
+                                        .iter()
+                                        .map(|i| extracted[*i].clone())
+                                        .collect_vec();
+                                    let encoded_new = idx_rel
+                                        .encode_key_for_store(&idx_tup_new, Default::default())?;
+                                    self.store_tx.put(&encoded_new, &[])?;
                                 }
                             }
+
                             if need_to_collect {
                                 old_tuples.push(DataValue::List(tup));
                             }
@@ -469,9 +483,13 @@ impl<'a> SessionTx<'a> {
                     let kv_bindings = bindings;
                     if propagate_triggers {
                         for trigger in &relation_store.put_triggers {
-                            let mut program =
-                                parse_script(trigger, &Default::default(), &db.algorithms, cur_vld)?
-                                    .get_single_program()?;
+                            let mut program = parse_script(
+                                trigger,
+                                &Default::default(),
+                                &db.algorithms,
+                                cur_vld,
+                            )?
+                            .get_single_program()?;
 
                             make_const_rule(
                                 &mut program,
@@ -487,7 +505,14 @@ impl<'a> SessionTx<'a> {
                             );
 
                             let (_, cleanups) = db
-                                .run_query(self, program, cur_vld, callback_targets, callback_collector, false)
+                                .run_query(
+                                    self,
+                                    program,
+                                    cur_vld,
+                                    callback_targets,
+                                    callback_collector,
+                                    false,
+                                )
                                 .map_err(|err| {
                                     if err.source_code().is_some() {
                                         err
diff --git a/cozo-core/src/runtime/db.rs b/cozo-core/src/runtime/db.rs
index 1bc3779a..ea1ab94b 100644
--- a/cozo-core/src/runtime/db.rs
+++ b/cozo-core/src/runtime/db.rs
@@ -89,10 +89,8 @@ pub struct CallbackDeclaration {
     callback: Box<dyn Fn(CallbackOp, NamedRows, NamedRows) + Send + Sync>,
 }
 
-pub(crate) type CallbackCollector = BTreeMap<
-    SmartString<LazyCompact>,
-    Vec<(CallbackOp, NamedRows, NamedRows)>,
->;
+pub(crate) type CallbackCollector =
+    BTreeMap<SmartString<LazyCompact>, Vec<(CallbackOp, NamedRows, NamedRows)>>;
 
 /// The database object of Cozo.
 #[derive(Clone)]
@@ -140,11 +138,7 @@ impl NamedRows {
         let rows = self
             .rows
             .into_iter()
-            .map(|row| {
-                row.into_iter()
-                    .map(|val| JsonValue::from(val))
-                    .collect::<JsonValue>()
-            })
+            .map(|row| row.into_iter().map(JsonValue::from).collect::<JsonValue>())
             .collect::<JsonValue>();
         json!({
             "headers": self.headers,
@@ -276,7 +270,7 @@ impl<'s, S: Storage<'s>> Db<S> {
         #[diagnostic(code(import::bad_data))]
         struct BadDataForRelation(String, JsonValue);
 
-        let rel_names = data.keys().map(|k| SmartString::from(k)).collect_vec();
+        let rel_names = data.keys().map(SmartString::from).collect_vec();
         let locks = self.obtain_relation_locks(rel_names.iter());
         let _guards = locks.iter().map(|l| l.read().unwrap()).collect_vec();
 
@@ -441,7 +435,7 @@ impl<'s, S: Storage<'s>> Db<S> {
 
         #[cfg(feature = "storage-sqlite")]
         {
-            let rel_names = relations.iter().map(|n| SmartString::from(n)).collect_vec();
+            let rel_names = relations.iter().map(SmartString::from).collect_vec();
             let locks = self.obtain_relation_locks(rel_names.iter());
             let _guards = locks.iter().map(|l| l.read().unwrap()).collect_vec();
 
@@ -569,7 +563,7 @@ impl<'s, S: Storage<'s>> Db<S> {
                 collected.push(lock);
             }
         }
-        return collected;
+        collected
     }
 
     fn compact_relation(&'s self) -> Result<()> {
@@ -670,10 +664,7 @@ impl<'s, S: Storage<'s>> Db<S> {
             .cloned()
             .collect()
     }
-    fn send_callbacks(
-        &'s self,
-        collector: CallbackCollector,
-    ) {
+    fn send_callbacks(&'s self, collector: CallbackCollector) {
         for (k, vals) in collector {
             for (op, new, old) in vals {
                 self.callback_sender
@@ -957,7 +948,7 @@ impl<'s, S: Storage<'s>> Db<S> {
                 }
             }
         }
-        return Ok(Left(ret));
+        Ok(Left(ret))
     }
     fn explain_compiled(&self, strata: &[CompiledProgram]) -> Result<NamedRows> {
         let mut ret: Vec<JsonValue> = vec![];
@@ -1192,7 +1183,10 @@ impl<'s, S: Storage<'s>> Db<S> {
                 })
             }
             SysOp::CreateIndex(rel_name, idx_name, cols) => {
-                let lock = self.obtain_relation_locks(iter::once(&rel_name.name)).pop().unwrap();
+                let lock = self
+                    .obtain_relation_locks(iter::once(&rel_name.name))
+                    .pop()
+                    .unwrap();
                 let _guard = lock.write().unwrap();
                 let mut tx = self.transact_write()?;
                 tx.create_index(&rel_name, &idx_name, cols)?;
@@ -1203,7 +1197,10 @@ impl<'s, S: Storage<'s>> Db<S> {
                 })
             }
             SysOp::RemoveIndex(rel_name, idx_name) => {
-                let lock = self.obtain_relation_locks(iter::once(&rel_name.name)).pop().unwrap();
+                let lock = self
+                    .obtain_relation_locks(iter::once(&rel_name.name))
+                    .pop()
+                    .unwrap();
                 let _guard = lock.read().unwrap();
                 let mut tx = self.transact_write()?;
                 tx.remove_index(&rel_name, &idx_name)?;
@@ -1260,11 +1257,7 @@ impl<'s, S: Storage<'s>> Db<S> {
                 }
                 let rows = rows
                     .into_iter()
-                    .map(|row| {
-                        row.into_iter()
-                            .map(|val| DataValue::from(val))
-                            .collect_vec()
-                    })
+                    .map(|row| row.into_iter().map(DataValue::from).collect_vec())
                     .collect_vec();
                 tx.commit_tx()?;
                 Ok(NamedRows {
@@ -1302,7 +1295,7 @@ impl<'s, S: Storage<'s>> Db<S> {
         cur_vld: ValidityTs,
         callback_targets: &BTreeSet<SmartString<LazyCompact>>,
         callback_collector: &mut CallbackCollector,
-        top_level: bool
+        top_level: bool,
     ) -> Result<(NamedRows, Vec<(Vec<u8>, Vec<u8>)>)> {
         // cleanups contain stored relations that should be deleted at the end of query
         let mut clean_ups = vec![];
@@ -1447,7 +1440,7 @@ impl<'s, S: Storage<'s>> Db<S> {
                         cur_vld,
                         callback_targets,
                         callback_collector,
-                        top_level
+                        top_level,
                     )
                     .wrap_err_with(|| format!("when executing against relation '{}'", meta.name))?;
                 clean_ups.extend(to_clear);
@@ -1502,7 +1495,7 @@ impl<'s, S: Storage<'s>> Db<S> {
                         cur_vld,
                         callback_targets,
                         callback_collector,
-                        top_level
+                        top_level,
                     )
                     .wrap_err_with(|| format!("when executing against relation '{}'", meta.name))?;
                 clean_ups.extend(to_clear);
@@ -1575,11 +1568,7 @@ impl<'s, S: Storage<'s>> Db<S> {
         tx.commit_tx()?;
         let rows = rows
             .into_iter()
-            .map(|row| {
-                row.into_iter()
-                    .map(|val| DataValue::from(val))
-                    .collect_vec()
-            })
+            .map(|row| row.into_iter().map(DataValue::from).collect_vec())
             .collect_vec();
         Ok(NamedRows {
             headers: vec![
@@ -1622,11 +1611,7 @@ impl<'s, S: Storage<'s>> Db<S> {
         }
         let rows = rows
             .into_iter()
-            .map(|row| {
-                row.into_iter()
-                    .map(|val| DataValue::from(val))
-                    .collect_vec()
-            })
+            .map(|row| row.into_iter().map(DataValue::from).collect_vec())
             .collect_vec();
         Ok(NamedRows {
             headers: vec![
diff --git a/cozo-core/src/runtime/relation.rs b/cozo-core/src/runtime/relation.rs
index 2c71bd2c..84c8a25c 100644
--- a/cozo-core/src/runtime/relation.rs
+++ b/cozo-core/src/runtime/relation.rs
@@ -24,6 +24,7 @@ use crate::data::symb::Symbol;
 use crate::data::tuple::{decode_tuple_from_key, Tuple, TupleT, ENCODED_KEY_MIN_LEN};
 use crate::data::value::{DataValue, ValidityTs};
 use crate::parse::SourceSpan;
+use crate::query::compile::IndexPositionUse;
 use crate::runtime::transact::SessionTx;
 use crate::{NamedRows, StoreTx};
 
@@ -151,6 +152,65 @@ impl RelationHandle {
         let prefix_bytes = self.id.0.to_be_bytes();
         data[0..8].copy_from_slice(&prefix_bytes);
     }
+    pub(crate) fn choose_index(
+        &self,
+        arg_uses: &[IndexPositionUse],
+        validity_query: bool,
+    ) -> Option<(RelationHandle, Vec<usize>, bool)> {
+        if self.indices.is_empty() {
+            return None;
+        }
+        let mut max_prefix_len = 0;
+        let key_len = self.metadata.keys.len();
+        for arg_use in arg_uses {
+            if *arg_use == IndexPositionUse::Join {
+                max_prefix_len += 1;
+                if max_prefix_len == key_len {
+                    break;
+                }
+            } else {
+                break;
+            }
+        }
+        let required_positions = arg_uses
+            .iter()
+            .enumerate()
+            .filter_map(|(i, pos_use)| {
+                if *pos_use != IndexPositionUse::Ignored {
+                    Some(i)
+                } else {
+                    None
+                }
+            })
+            .collect_vec();
+        let mut chosen = None;
+        for (manifest, mapper) in self.indices.values() {
+            if validity_query && *mapper.last().unwrap() != self.metadata.keys.len() - 1 {
+                continue;
+            }
+
+            let mut cur_prefix_len = 0;
+            for i in mapper {
+                if arg_uses[*i] == IndexPositionUse::Join {
+                    cur_prefix_len += 1;
+                } else {
+                    break;
+                }
+            }
+            if cur_prefix_len > max_prefix_len {
+                max_prefix_len = cur_prefix_len;
+                let mut need_join = false;
+                for need_pos in required_positions.iter() {
+                    if !mapper.contains(need_pos) {
+                        need_join = true;
+                        break;
+                    }
+                }
+                chosen = Some((manifest.clone(), mapper.clone(), need_join))
+            }
+        }
+        chosen
+    }
     pub(crate) fn encode_key_for_store(&self, tuple: &Tuple, span: SourceSpan) -> Result<Vec<u8>> {
         let len = self.metadata.keys.len();
         ensure!(
@@ -465,10 +525,8 @@ impl<'a> SessionTx<'a> {
             if self.store_tx.exists(&encoded, true)? {
                 bail!(RelNameConflictError(input_meta.name.to_string()))
             };
-        } else {
-            if self.temp_store_tx.exists(&encoded, true)? {
-                bail!(RelNameConflictError(input_meta.name.to_string()))
-            };
+        } else if self.temp_store_tx.exists(&encoded, true)? {
+            bail!(RelNameConflictError(input_meta.name.to_string()))
         }
 
         let metadata = input_meta.metadata.clone();
@@ -543,7 +601,7 @@ impl<'a> SessionTx<'a> {
         }
 
         for k in store.indices.keys() {
-            self.destroy_relation(&format!("{}:{}", name, k))?;
+            self.destroy_relation(&format!("{name}:{k}"))?;
         }
 
         let key = DataValue::from(name);
@@ -587,7 +645,7 @@ impl<'a> SessionTx<'a> {
         }
 
         let mut col_defs = vec![];
-        for col in cols.iter() {
+        'outer: for col in cols.iter() {
             for orig_col in rel_handle
                 .metadata
                 .keys
@@ -596,7 +654,7 @@ impl<'a> SessionTx<'a> {
             {
                 if orig_col.name == col.name {
                     col_defs.push(orig_col.clone());
-                    break;
+                    continue 'outer;
                 }
             }
 
diff --git a/cozo-lib-java/src/lib.rs b/cozo-lib-java/src/lib.rs
index 5fc48503..c42a4e17 100644
--- a/cozo-lib-java/src/lib.rs
+++ b/cozo-lib-java/src/lib.rs
@@ -45,7 +45,7 @@ pub extern "system" fn Java_org_cozodb_CozoJavaBridge_openDb(
     let engine: String = env.get_string(engine).unwrap().into();
     let path: String = env.get_string(path).unwrap().into();
     let options: String = env.get_string(options).unwrap().into();
-    let id = match DbInstance::new(&engine, &path, &options) {
+    let id = match DbInstance::new(&engine, path, &options) {
         Ok(db) => {
             let id = HANDLES.current.fetch_add(1, Ordering::AcqRel);
             let mut dbs = HANDLES.dbs.lock().unwrap();
@@ -139,7 +139,7 @@ pub extern "system" fn Java_org_cozodb_CozoJavaBridge_backup(
     match get_db(id) {
         None => env.new_string(DB_NOT_FOUND).unwrap().into_raw(),
         Some(db) => {
-            let res = db.backup_db_str(&file);
+            let res = db.backup_db_str(file);
             env.new_string(res).unwrap().into_raw()
         }
     }
@@ -156,7 +156,7 @@ pub extern "system" fn Java_org_cozodb_CozoJavaBridge_restore(
     match get_db(id) {
         None => env.new_string(DB_NOT_FOUND).unwrap().into_raw(),
         Some(db) => {
-            let res = db.restore_backup_str(&file);
+            let res = db.restore_backup_str(file);
             env.new_string(res).unwrap().into_raw()
         }
     }
diff --git a/cozo-lib-nodejs/src/lib.rs b/cozo-lib-nodejs/src/lib.rs
index 4baa3510..fc18dfde 100644
--- a/cozo-lib-nodejs/src/lib.rs
+++ b/cozo-lib-nodejs/src/lib.rs
@@ -28,7 +28,7 @@ fn open_db(mut cx: FunctionContext) -> JsResult<JsNumber> {
     let engine = cx.argument::<JsString>(0)?.value(&mut cx);
     let path = cx.argument::<JsString>(1)?.value(&mut cx);
     let options = cx.argument::<JsString>(2)?.value(&mut cx);
-    match DbInstance::new(&engine, &path, &options) {
+    match DbInstance::new(&engine, path, &options) {
         Ok(db) => {
             let id = HANDLES.current.fetch_add(1, Ordering::AcqRel);
             let mut dbs = HANDLES.dbs.lock().unwrap();
diff --git a/cozo-lib-python/src/lib.rs b/cozo-lib-python/src/lib.rs
index 685fe715..7d749b17 100644
--- a/cozo-lib-python/src/lib.rs
+++ b/cozo-lib-python/src/lib.rs
@@ -40,7 +40,7 @@ fn py_to_value(ob: &PyAny) -> PyResult<DataValue> {
         }
         DataValue::List(coll)
     } else {
-        return Err(PyException::new_err(format!("Cannot convert {} into Cozo value", ob)).into());
+        return Err(PyException::new_err(format!("Cannot convert {ob} into Cozo value")));
     })
 }
 
diff --git a/cozoserver/src/main.rs b/cozoserver/src/main.rs
index 8e896044..c0ec1dae 100644
--- a/cozoserver/src/main.rs
+++ b/cozoserver/src/main.rs
@@ -95,13 +95,10 @@ fn main() {
                 .run_script("::running", Default::default())
                 .expect("Cannot determine running queries");
             for row in running.rows {
-                let id = row.into_iter().next().unwrap().get_int().unwrap();
+                let id = row.into_iter().next().unwrap();
                 eprintln!("Killing running query {id}");
                 db_copy
-                    .run_script(
-                        "::kill $id",
-                        BTreeMap::from([("id".to_string(), json!(id))]),
-                    )
+                    .run_script("::kill $id", BTreeMap::from([("id".to_string(), id)]))
                     .expect("Cannot kill process");
             }
         })
@@ -170,7 +167,9 @@ fn server_main(args: Args, db: DbInstance) {
                     }
 
                     let payload: QueryPayload = try_or_400!(rouille::input::json_input(request));
-                    let result = db.run_script_fold_err(&payload.script, payload.params);
+                    let params = payload.params.into_iter().map(|(k, v)|
+                    (k, DataValue::from(v))).collect();
+                    let result = db.run_script_fold_err(&payload.script, params);
                     let response = Response::json(&result);
                     if let Some(serde_json::Value::Bool(true)) = result.get("ok") {
                         response
diff --git a/cozoserver/src/repl.rs b/cozoserver/src/repl.rs
index 9d2825e3..6b0a4e5d 100644
--- a/cozoserver/src/repl.rs
+++ b/cozoserver/src/repl.rs
@@ -16,7 +16,7 @@ use std::io::{Read, Write};
 use miette::{bail, miette, IntoDiagnostic};
 use serde_json::{json, Value};
 
-use cozo::DbInstance;
+use cozo::{DataValue, DbInstance};
 
 struct Indented;
 
@@ -104,7 +104,7 @@ pub(crate) fn repl_main(db: DbInstance) -> Result<(), Box<dyn Error>> {
 fn process_line(
     line: &str,
     db: &DbInstance,
-    params: &mut BTreeMap<String, Value>,
+    params: &mut BTreeMap<String, DataValue>,
     save_next: &mut Option<String>,
 ) -> miette::Result<()> {
     let line = line.trim();
@@ -143,7 +143,7 @@ fn process_line(
                 if path.is_empty() {
                     bail!("Backup requires a path");
                 };
-                db.backup_db(path.to_string())?;
+                db.backup_db(path)?;
                 println!("Backup written successfully to {path}")
             }
             "restore" => {