Verify exactly one snapshot when reading last in tests

- use `computeScalar` wherever possible
- use `FETCH FIRST 1 ROW WITH TIES` instead of just `LIMIT 1`, so that
  test fails if there is a tie (ambiguity).

plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseIcebergConnectorTest.java

@@ -1049,8 +1049,7 @@ public void testRollbackSnapshot()
 
     private long getLatestSnapshotId(String tableName)
     {
-        return (long) computeActual(format("SELECT snapshot_id FROM \"%s$snapshots\" ORDER BY committed_at DESC LIMIT 1", tableName))
-                .getOnlyValue();
+        return (long) computeScalar(format("SELECT snapshot_id FROM \"%s$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES", tableName));
     }
 
     @Override
@@ -5278,7 +5277,7 @@ private List<Long> getSnapshotIds(String tableName)
 
     private long getCurrentSnapshotId(String tableName)
     {
-        return (long) computeScalar("SELECT snapshot_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC LIMIT 1");
+        return (long) computeScalar("SELECT snapshot_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES");
     }
 
     private Path getIcebergTableDataPath(String tableLocation)

plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/BaseSharedMetastoreTest.java

@@ -180,13 +180,12 @@ public void testTimeTravelWithRedirection()
 
     private long getLatestSnapshotId(String schema)
     {
-        return (long) computeActual(format("SELECT snapshot_id FROM iceberg.%s.\"nation_test$snapshots\" ORDER BY committed_at DESC LIMIT 1", schema))
-                .getOnlyValue();
+        return (long) computeScalar(format("SELECT snapshot_id FROM iceberg.%s.\"nation_test$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES", schema));
     }
 
     private long getCommittedAtInEpochMilliSeconds(long snapshotId, String schema)
     {
-        return ((ZonedDateTime) computeActual(format("SELECT committed_at FROM iceberg.%s.\"nation_test$snapshots\" WHERE snapshot_id=%s LIMIT 1", schema, snapshotId)).getOnlyValue())
+        return ((ZonedDateTime) computeScalar(format("SELECT committed_at FROM iceberg.%s.\"nation_test$snapshots\" WHERE snapshot_id=%s", schema, snapshotId)))
                 .toInstant().toEpochMilli();
     }
 

plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/TestIcebergMetadataFileOperations.java

@@ -355,8 +355,7 @@ private Multiset<FileOperation> getOperations()
 
     private long getLatestSnapshotId(String tableName)
     {
-        return (long) computeActual(format("SELECT snapshot_id FROM \"%s$snapshots\" ORDER BY committed_at DESC LIMIT 1", tableName))
-                .getOnlyValue();
+        return (long) computeScalar(format("SELECT snapshot_id FROM \"%s$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES", tableName));
     }
 
     static class FileOperation

plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/TestIcebergReadVersionedTable.java

@@ -103,13 +103,12 @@ public void testSystemTables()
 
     private long getLatestSnapshotId(String tableName)
     {
-        return (long) computeActual(format("SELECT snapshot_id FROM \"%s$snapshots\" ORDER BY committed_at DESC LIMIT 1", tableName))
-                .getOnlyValue();
+        return (long) computeScalar(format("SELECT snapshot_id FROM \"%s$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES", tableName));
     }
 
     private long getCommittedAtInEpochMilliSeconds(String tableName, long snapshotId)
     {
-        return ((ZonedDateTime) computeActual(format("SELECT committed_at FROM \"%s$snapshots\" WHERE snapshot_id=%s LIMIT 1", tableName, snapshotId)).getOnlyValue())
+        return ((ZonedDateTime) computeScalar(format("SELECT committed_at FROM \"%s$snapshots\" WHERE snapshot_id=%s", tableName, snapshotId)))
                 .toInstant().toEpochMilli();
     }
 

plugin/trino-iceberg/src/test/java/io/trino/plugin/iceberg/TestIcebergV2.java

@@ -423,9 +423,9 @@ public void testDeletingEntireFileWithMultipleSplits()
 
         assertThat(this.loadTable(tableName).newScan().planFiles()).hasSize(1);
         // Ensure only one snapshot is committed to the table
-        Long initialSnapshotId = (Long) computeActual("SELECT snapshot_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC LIMIT 1").getOnlyValue();
+        long initialSnapshotId = (long) computeScalar("SELECT snapshot_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES");
         assertUpdate("DELETE FROM " + tableName + " WHERE regionkey < 10", 25);
-        Long parentSnapshotId = (Long) computeActual("SELECT parent_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC LIMIT 1").getOnlyValue();
+        long parentSnapshotId = (long) computeScalar("SELECT parent_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES");
         assertEquals(initialSnapshotId, parentSnapshotId);
         assertThat(query("SELECT * FROM " + tableName)).returnsEmptyResult();
         assertThat(this.loadTable(tableName).newScan().planFiles()).hasSize(0);
@@ -439,9 +439,9 @@ public void testMultipleDeletes()
         assertUpdate("CREATE TABLE " + tableName + " AS SELECT * FROM tpch.tiny.nation", 25);
         assertThat(this.loadTable(tableName).newScan().planFiles()).hasSize(1);
         // Ensure only one snapshot is committed to the table
-        Long initialSnapshotId = (Long) computeActual("SELECT snapshot_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC LIMIT 1").getOnlyValue();
+        long initialSnapshotId = (long) computeScalar("SELECT snapshot_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES");
         assertUpdate("DELETE FROM " + tableName + " WHERE regionkey % 2 = 1", "SELECT count(*) FROM nation WHERE regionkey % 2 = 1");
-        Long parentSnapshotId = (Long) computeActual("SELECT parent_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC LIMIT 1").getOnlyValue();
+        long parentSnapshotId = (long) computeScalar("SELECT parent_id FROM \"" + tableName + "$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES");
         assertEquals(initialSnapshotId, parentSnapshotId);
 
         assertUpdate("DELETE FROM " + tableName + " WHERE regionkey % 2 = 0", "SELECT count(*) FROM nation WHERE regionkey % 2 = 0");

testing/trino-product-tests/src/main/java/io/trino/tests/product/iceberg/TestIcebergOptimize.java

@@ -103,7 +103,8 @@ private List<String> getActiveFiles(String catalog, String schema, String tableN
 
     private long getCurrentSnapshotId(String catalog, String schema, String tableName)
     {
-        return (long) getOnlyElement(getOnlyElement(onTrino().executeQuery(format("SELECT snapshot_id FROM %s.%s.\"%s$snapshots\" ORDER BY committed_at DESC LIMIT 1", catalog, schema, tableName)).rows()));
+        return (long) getOnlyElement(getOnlyElement(onTrino().executeQuery(
+                format("SELECT snapshot_id FROM %s.%s.\"%s$snapshots\" ORDER BY committed_at DESC FETCH FIRST 1 ROW WITH TIES", catalog, schema, tableName)).rows()));
     }
 
     private static String sparkTableName(String tableName)

testing/trino-product-tests/src/main/java/io/trino/tests/product/iceberg/TestIcebergProcedureCalls.java

@@ -50,7 +50,7 @@ public void testRollbackToSnapshot()
     private long getSecondOldestTableSnapshot(String tableName)
     {
         return (Long) onTrino().executeQuery(
-                format("SELECT snapshot_id FROM iceberg.default.\"%s$snapshots\" WHERE parent_id IS NOT NULL ORDER BY committed_at LIMIT 1", tableName))
+                format("SELECT snapshot_id FROM iceberg.default.\"%s$snapshots\" WHERE parent_id IS NOT NULL ORDER BY committed_at FETCH FIRST 1 ROW WITH TIES", tableName))
                 .row(0)
                 .get(0);
     }