fix: correct search interval vs item datetime interval (#1071)

resolves #1070

### Description

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- [ ] Unit tests
- [ ] Documentation, including doctests
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Author: hrodmn

crates/duckdb/data/sentinel-1-global-mosaics.parquet

@@ -363,8 +363,8 @@ impl Client {
             if let Some(start) = interval.0 {
                 wheres.push(format!(
                     "?::TIMESTAMPTZ <= {}",
-                    if has_start_datetime {
-                        "start_datetime"
+                    if has_end_datetime {
+                        "coalesce(end_datetime, datetime)"
                     } else {
                         "datetime"
                     }
@@ -374,8 +374,8 @@ impl Client {
             if let Some(end) = interval.1 {
                 wheres.push(format!(
                     "?::TIMESTAMPTZ >= {}", // Inclusive, https://github.com/radiantearth/stac-spec/pull/1280
-                    if has_end_datetime {
-                        "end_datetime"
+                    if has_start_datetime {
+                        "coalesce(start_datetime, datetime)"
                     } else {
                         "datetime"
                     }
@@ -855,6 +855,17 @@ mod tests {
         assert_eq!(item_collection.items.len(), 1);
     }
 
+    #[rstest]
+    fn search_datetime_start_end_datetime(client: Client) {
+        let item_collection = client
+            .search(
+                "data/sentinel-1-global-mosaics.parquet",
+                Search::default().datetime("2026-04-15T00:00:00Z"),
+            )
+            .unwrap();
+        assert_eq!(item_collection.items.len(), 1);
+    }
+
     #[rstest]
     fn search_limit(client: Client) {
         let item_collection = client