feat: let a computed-column batch read its own earlier declarations

`add_columns().computed()` accepted several columns in one call but bound each against the table's schema as it stood before the call, so `a` and `b = a + 1` had to be two commits. A server staging declarations behind other schema work has no atomic way to do that, and a caller reading the builder's plural signature reasonably expects the batch to be one. Each accepted column now joins the schema the next one resolves against, so the batch is planned and committed as one. Order is the dependency order; reading ahead is still an unknown column. `validate_declarations` exposes the same check without a commit, for callers that must reject before earlier work in the same request lands. Dependent columns need refresh to be dependency-aware, or `b = coalesce(a, 0)` refreshed before `a` bakes zeros from `a`'s placeholder null and the fill-once contract keeps them. Refresh now fills a column's computed inputs first, each as its own commit, then reads the committed values. Two concurrent fills of one input collide on its field in lance's conflict check, so a dependent fill can only commit over inputs that were durable when it read them. `rows_filled` counts the requested column only.
chore: update lance dependency to v12.0.0-beta.2
2026-08-27 16:38:31 +00:00 · 2026-08-27 16:26:14 +00:00 · 2026-08-26 01:31:44 +00:00
5 changed files with 187 additions and 67 deletions
@@ -3455,8 +3455,8 @@ checksum = "42703706b716c37f96a77aea830392ad231f44c9e9a67872fa5548707e11b11c"

 [[package]]
 name = "fsst"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "rand 0.9.5",
@@ -4815,8 +4815,8 @@ checksum = "e037a2e1d8d5fdbd49b16a4ea09d5d6401c1f29eca5ff29d03d3824dba16256a"

 [[package]]
 name = "lance"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arc-swap",
 "arrow",
@@ -4888,8 +4888,8 @@ dependencies = [

 [[package]]
 name = "lance-arrow"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-buffer",
@@ -4911,7 +4911,7 @@ dependencies = [
 [[package]]
 name = "lance-arrow-scalar"
 version = "58.0.0"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-buffer",
@@ -4925,7 +4925,7 @@ dependencies = [
 [[package]]
 name = "lance-arrow-stats"
 version = "58.0.0"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-schema",
@@ -4934,8 +4934,8 @@ dependencies = [

 [[package]]
 name = "lance-bitpacking"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrayref",
 "crunchy",
@@ -4945,8 +4945,8 @@ dependencies = [

 [[package]]
 name = "lance-core"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-buffer",
@@ -4983,8 +4983,8 @@ dependencies = [

 [[package]]
 name = "lance-datafusion"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow",
 "arrow-array",
@@ -5013,8 +5013,8 @@ dependencies = [

 [[package]]
 name = "lance-datagen"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow",
 "arrow-array",
@@ -5031,8 +5031,8 @@ dependencies = [

 [[package]]
 name = "lance-derive"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "proc-macro2",
 "quote",
@@ -5041,8 +5041,8 @@ dependencies = [

 [[package]]
 name = "lance-encoding"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-arith",
 "arrow-array",
@@ -5075,8 +5075,8 @@ dependencies = [

 [[package]]
 name = "lance-file"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-arith",
 "arrow-array",
@@ -5107,8 +5107,8 @@ dependencies = [

 [[package]]
 name = "lance-index"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arc-swap",
 "arrow",
@@ -5172,8 +5172,8 @@ dependencies = [

 [[package]]
 name = "lance-index-core"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-schema",
@@ -5195,8 +5195,8 @@ dependencies = [

 [[package]]
 name = "lance-io"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow",
 "arrow-array",
@@ -5236,8 +5236,8 @@ dependencies = [

 [[package]]
 name = "lance-linalg"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-schema",
@@ -5251,8 +5251,8 @@ dependencies = [

 [[package]]
 name = "lance-namespace"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow",
 "async-trait",
@@ -5264,8 +5264,8 @@ dependencies = [

 [[package]]
 name = "lance-namespace-impls"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow",
 "arrow-ipc",
@@ -5318,8 +5318,8 @@ dependencies = [

 [[package]]
 name = "lance-select"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-buffer",
@@ -5333,8 +5333,8 @@ dependencies = [

 [[package]]
 name = "lance-table"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow",
 "arrow-array",
@@ -5374,8 +5374,8 @@ dependencies = [

 [[package]]
 name = "lance-testing"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "arrow-array",
 "arrow-schema",
@@ -5388,8 +5388,8 @@ dependencies = [

 [[package]]
 name = "lance-tokenizer"
-version = "12.0.0-beta.1"
-source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.1#e37cee4397abc6a71df3cdfa0e637c274f820aa6"
+version = "12.0.0-beta.2"
+source = "git+https://github.com/lance-format/lance.git?tag=v12.0.0-beta.2#dafa4642658d996b3e31dde91e02f72db7860d7e"
 dependencies = [
 "frostem",
 "icu_segmenter",
@@ -13,20 +13,20 @@ categories = ["database-implementations"]
 rust-version = "1.91.0"

 [workspace.dependencies]
-lance = { "version" = "=12.0.0-beta.1", default-features = false, "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-core = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-datagen = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-file = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-io = { "version" = "=12.0.0-beta.1", default-features = false, "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-index = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-linalg = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-namespace = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-namespace-impls = { "version" = "=12.0.0-beta.1", default-features = false, "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-table = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-testing = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-datafusion = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-encoding = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
-lance-arrow = { "version" = "=12.0.0-beta.1", "tag" = "v12.0.0-beta.1", "git" = "https://github.com/lance-format/lance.git" }
+lance = { "version" = "=12.0.0-beta.2", default-features = false, "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-core = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-datagen = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-file = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-io = { "version" = "=12.0.0-beta.2", default-features = false, "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-index = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-linalg = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-namespace = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-namespace-impls = { "version" = "=12.0.0-beta.2", default-features = false, "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-table = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-testing = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-datafusion = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-encoding = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
+lance-arrow = { "version" = "=12.0.0-beta.2", "tag" = "v12.0.0-beta.2", "git" = "https://github.com/lance-format/lance.git" }
 lancedb = { path = "rust/lancedb", default-features = false }
 ahash = "0.8"
 # Note that this one does not include pyarrow
@@ -28,7 +28,7 @@
    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <arrow.version>15.0.0</arrow.version>
-        <lance-core.version>12.0.0-beta.1</lance-core.version>
+        <lance-core.version>12.0.0-beta.2</lance-core.version>
        <spotless.skip>false</spotless.skip>
        <spotless.version>2.30.0</spotless.version>
        <spotless.java.googlejavaformat.version>1.7</spotless.java.googlejavaformat.version>
@@ -22,7 +22,7 @@
 use std::collections::{BTreeSet, HashMap};
 use std::sync::Arc;

-use arrow_schema::{DataType, Field as ArrowField, Schema as ArrowSchema, SchemaRef};
+use arrow_schema::{DataType, Field as ArrowField, Fields, Schema as ArrowSchema, SchemaRef};
 use datafusion_common::tree_node::TreeNode;
 use datafusion_physical_plan::PhysicalExpr;
 use lance::dataset::NewColumnTransform;
@@ -1273,6 +1273,11 @@ pub(crate) fn bind(schema: SchemaRef, column: &str, expression: &str) -> Result<
 /// refresh time: that the expression parses, that every column it reads
 /// exists, and that the target name is free. A declaration that survives this
 /// is one a refresh can always act on.
+///
+/// Each accepted column joins the schema the next one resolves against, so a
+/// batch may declare `a` and then `b = a + 1` in one commit. Refresh fills a
+/// column's computed inputs before the column, so the order of refresh calls
+/// does not matter.
 pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Vec<ArrowField>> {
    if columns.is_empty() {
        return Err(Error::InvalidInput {
@@ -1280,11 +1285,11 @@ pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Ve
        });
    }

+    let mut schema = schema;
    let mut fields = Vec::with_capacity(columns.len());
-    let mut declared: Vec<&str> = Vec::with_capacity(columns.len());

    for (name, expression) in columns {
-        if schema.field_with_name(name).is_ok() || declared.contains(&name.as_str()) {
+        if schema.field_with_name(name).is_ok() {
            return Err(Error::ColumnAlreadyExists { name: name.clone() });
        }

@@ -1292,16 +1297,31 @@ pub(crate) fn plan(schema: SchemaRef, columns: &[(String, String)]) -> Result<Ve

        // Declared columns start entirely null, so nullability is a property
        // of the declaration rather than of what the expression yields.
-        fields.push(
-            ArrowField::new(name, bound.data_type, true)
-                .with_metadata(computed_column_metadata(expression, &bound.inputs)),
-        );
-        declared.push(name);
+        let field = ArrowField::new(name, bound.data_type, true)
+            .with_metadata(computed_column_metadata(expression, &bound.inputs));
+        schema = Arc::new(ArrowSchema::new_with_metadata(
+            schema
+                .fields()
+                .iter()
+                .cloned()
+                .chain(std::iter::once(Arc::new(field.clone())))
+                .collect::<Fields>(),
+            schema.metadata().clone(),
+        ));
+        fields.push(field);
    }

    Ok(fields)
 }

+/// Check `(name, expression)` pairs against `schema` exactly as
+/// [`AddColumnsBuilder::computed`](super::AddColumnsBuilder::computed) will
+/// admit them, without committing. For callers that stage declarations
+/// behind other work and need the rejection before any of it lands.
+pub fn validate_declarations(schema: SchemaRef, columns: &[(String, String)]) -> Result<()> {
+    plan(schema, columns).map(drop)
+}
+
 /// Build the transform that declares `columns` against `schema`.
 ///
 /// An all-null column is how a binding with no values yet is carried into a
@@ -1582,6 +1602,40 @@ mod tests {
        assert!(declared(&table).await.is_empty());
    }

+    /// A batch may build on itself: one commit, and the later entry's inputs
+    /// name the earlier one.
+    #[tokio::test]
+    async fn test_a_declaration_may_read_one_declared_before_it() {
+        let table = table_with_ints("chain").await;
+        let before = table.version().await.unwrap();
+        add_computed(
+            &table,
+            &[("a".into(), "x + 1".into()), ("b".into(), "a * 2".into())],
+        )
+        .await
+        .unwrap();
+        assert_eq!(table.version().await.unwrap(), before + 1);
+        let declared = declared(&table).await;
+        assert_eq!(declared[1].name, "b");
+        assert_eq!(declared[1].inputs, vec!["a".to_string()]);
+
+        // Order is the dependency order; reading ahead is still unknown.
+        let err = add_computed(
+            &table,
+            &[("c".into(), "d + 1".into()), ("d".into(), "x + 1".into())],
+        )
+        .await
+        .unwrap_err();
+        assert!(matches!(err, Error::InvalidExpression { column, .. } if column == "c"));
+        assert!(
+            validate_declarations(
+                table.schema().await.unwrap(),
+                &[("e".into(), "random()".into())]
+            )
+            .is_err()
+        );
+    }
+
    /// A column added by an ordinary transform is materialized, not bound, so
    /// it carries no declaration to report.
    #[tokio::test]
@@ -7,6 +7,12 @@
 //! therefore idempotent and does not observe input mutation -- once a row is
 //! filled, changing what the expression reads leaves the stored result alone.
 //!
+//! A column's computed inputs are filled first, each by its own refresh and
+//! commit, so the expression never reads an input's placeholder null as a
+//! value. Two concurrent fills of one input collide on its field in lance's
+//! conflict check, so a dependent fill can only commit over inputs that were
+//! already durable when it read them.
+//!
 //! Two passes per fragment. The first scans only the unfilled live rows and
 //! evaluates the expression over them, which yields the exact fill count and
 //! decides whether the fragment is staged at all -- a fragment where nothing
@@ -41,7 +47,8 @@ use crate::{Error, Result};
 /// The result of refreshing a computed column.
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize, Default)]
 pub struct RefreshColumnResult {
-    /// Rows that had a value computed.
+    /// Rows that had a value computed, in the requested column only; inputs
+    /// filled on its behalf are not counted.
    #[serde(default)]
    pub rows_filled: u64,
    /// The commit version associated with the operation.
@@ -74,7 +81,35 @@ async fn execute_refresh_column_with_source(

    let expression = declared_expression(&dataset, column)?;
    let schema = Arc::new(ArrowSchema::from(dataset.schema()));
-    let bound = Arc::new(super::computed_columns::bind(schema, column, &expression)?);
+    let bound = Arc::new(super::computed_columns::bind(
+        schema.clone(),
+        column,
+        &expression,
+    )?);
+
+    // Inputs that are themselves computed are filled first, so their
+    // placeholder nulls are never read as values. Declarations are acyclic by
+    // construction: a column can only read what existed when it was declared.
+    for input in &bound.roots {
+        let Some(declaration) = schema
+            .field_with_name(input)
+            .ok()
+            .and_then(computed_column_from_field)
+        else {
+            continue;
+        };
+        if !matches!(declaration.kind, ComputedColumnKind::Sql { .. }) {
+            return Err(Error::NotSupported {
+                message: format!(
+                    "computed column '{column}' reads '{input}', which this refresh cannot \
+                     fill first; refresh '{input}' before '{column}'"
+                ),
+            });
+        }
+        Box::pin(execute_refresh_column_with_source(table, input)).await?;
+    }
+    // Re-read: the input fills above committed on this handle.
+    let dataset = table.dataset.get().await?;
    let field = dataset
        .schema()
        .field(column)
@@ -414,6 +449,37 @@ mod tests {
        table.add(batch).execute().await.unwrap();
    }

+    /// The gate's reproducer: `b = coalesce(a, 0)` refreshed before `a`
+    /// must not bake zeros from `a`'s placeholder null.
+    #[tokio::test]
+    async fn test_dependent_refresh_cannot_fill_from_placeholder_null() {
+        let table = table_with("dependent_refresh_order", vec![1, 2, 3]).await;
+        table
+            .add_columns()
+            .computed("a", "x + 1")
+            .computed("b", "coalesce(a, 0)")
+            .execute()
+            .await
+            .unwrap();
+
+        let result = table.refresh_column("b").await.unwrap();
+        assert_eq!(result.rows_filled, 3);
+        assert_eq!(read(&table, "a").await, vec![Some(2), Some(3), Some(4)]);
+        assert_eq!(
+            table.count_rows(Some("b = a".to_string())).await.unwrap(),
+            3
+        );
+        assert_eq!(table.refresh_column("a").await.unwrap().rows_filled, 0);
+
+        // Appended rows: the input is filled in the new fragment first too.
+        append(&table, vec![10]).await;
+        assert_eq!(table.refresh_column("b").await.unwrap().rows_filled, 1);
+        assert_eq!(
+            table.count_rows(Some("b = 0".to_string())).await.unwrap(),
+            0
+        );
+    }
+
    #[tokio::test]
    async fn test_refresh_fills_a_declared_column() {
        let table = table_with("refresh_fills", vec![1, 2, 3]).await;