fix(prqlc, sort): do not require sort columns if it's followed by an aggregation

CHANGELOG.md

@@ -8,6 +8,9 @@
 
 **Fixes**:
 
+- `sort` step before an `aggregate` step no longer requires its columns in order
+  to avoid a group by clause error. (@julien-pinchelimouroux, #5347)
+
 **Documentation**:
 
 **Web**:
@@ -21,6 +24,8 @@
 
 **New Contributors**:
 
+- @julien-pinchelimouroux, with #5347
+
 ## 0.13.4 — 2025-03-26
 
 0.13.4 is a small bugfix release.

prqlc/prqlc/src/sql/pq/anchor.rs

@@ -500,7 +500,10 @@ pub(super) fn get_requirements(
         Super(Filter(expr)) | SqlTransform::Join { filter: expr, .. } => {
             CidCollector::collect(expr.clone())
         }
-        Super(Sort(sorts)) => sorts.iter().map(|s| s.column).collect(),
+        // Aggregations require that all selected columns be wrapped in aggregate functions (e.g., SUM, COUNT).
+        Super(Sort(sorts)) if !following.contains("Aggregate") => {
+            sorts.iter().map(|s| s.column).collect()
+        }
         Super(Take(rq::Take { range, .. })) => {
             let mut cids = Vec::new();
             if let Some(e) = &range.start {

prqlc/prqlc/tests/integration/sql.rs

@@ -1308,6 +1308,21 @@ fn test_sorts_03() {
     ");
 }
 
+#[test]
+fn test_sort_before_aggregate() {
+    assert_snapshot!((compile(r#"
+    from a
+    sort a.col
+    aggregate { result = sum a.col_to_agg }
+    "#
+    ).unwrap()), @r"
+    SELECT
+      COALESCE(SUM(col_to_agg), 0) AS result
+    FROM
+      a
+    ");
+}
+
 #[test]
 fn test_numbers() {
     let query = r###"