IGNITE-28341: Fix incorrect WHERE condition pushdown for LEFT OUTER JOIN in GridSqlQuerySplitter

modules/benchmarks/src/main/java/org/apache/ignite/internal/benchmarks/jmh/sql/JmhSqlJoinBenchmark.java

@@ -19,7 +19,9 @@
 
 import java.util.List;
 import java.util.concurrent.ThreadLocalRandom;
+import java.util.concurrent.atomic.AtomicInteger;
 import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.infra.Blackhole;
 import org.openjdk.jmh.runner.Runner;
 import org.openjdk.jmh.runner.options.Options;
 import org.openjdk.jmh.runner.options.OptionsBuilder;
@@ -34,6 +36,9 @@ public class JmhSqlJoinBenchmark extends JmhSqlAbstractBenchmark {
     /** Count of entries in EMP table. */
     protected static final int EMP_CNT = 10_000;
 
+    /** Counter for forcing query replanning in cold benchmark. */
+    private final AtomicInteger planRnd = new AtomicInteger();
+
     /**
      * Initiate new tables.
      */
@@ -59,14 +64,67 @@ public class JmhSqlJoinBenchmark extends JmhSqlAbstractBenchmark {
      * Colocated distributed join.
      */
     @Benchmark
-    public void colocatedDistributedJoin() {
+    public void colocatedDistributedJoin(Blackhole bh) {
         int key = ThreadLocalRandom.current().nextInt(EMP_CNT / BATCH_SIZE);
 
         List<List<?>> res = executeSql("SELECT emp.name, dept.name FROM emp JOIN dept ON emp.deptid = dept.deptid " +
                 "WHERE emp.salary = ?", key);
 
-        if (res.size() != BATCH_SIZE)
-            throw new AssertionError("Unexpected result size: " + res.size());
+        bh.consume(res);
+    }
+
+    /**
+     * LEFT JOIN with DISTINCT subquery - regression test for query splitter optimization.
+     * DISTINCT is applied to the smaller table (dept), then LEFT JOINed with the larger table (emp),
+     * and filtered by a condition on the right table.
+     */
+    @Benchmark
+    public void leftJoinDistinctRegression(Blackhole bh) {
+        List<List<?>> res = executeSql(
+                "SELECT d.deptid, d.name, e.empid " +
+                        "FROM (SELECT DISTINCT * FROM dept) d " +
+                        "LEFT JOIN emp e ON d.deptid = e.deptid " +
+                        "WHERE e.name = ?",
+                "Employee 5"
+        );
+
+        bh.consume(res);
+    }
+
+    /**
+     * LEFT JOIN without DISTINCT subquery - baseline for comparison.
+     */
+    @Benchmark
+    public void leftJoinNoDistinctBaseline(Blackhole bh) {
+        List<List<?>> res = executeSql(
+                "SELECT e.empid, e.name, d.deptid " +
+                        "FROM emp e " +
+                        "LEFT JOIN dept d ON e.deptid = d.deptid " +
+                        "WHERE d.name = ?",
+                "Department 5"
+        );
+
+        bh.consume(res);
+    }
+
+    /**
+     * LEFT JOIN with DISTINCT where query text is changed every run to bypass plan cache.
+     * This tests the cold path where query optimization and planning happens every time.
+     */
+    @Benchmark
+    public void leftJoinDistinctRegressionCold(Blackhole bh) {
+        int rnd = planRnd.incrementAndGet();
+
+        List<List<?>> res = executeSql(
+                "/*rnd=" + rnd + "*/ " +
+                        "SELECT d.deptid, d.name, e.empid " +
+                        "FROM (SELECT DISTINCT * FROM dept) d " +
+                        "LEFT JOIN emp e ON d.deptid = e.deptid " +
+                        "WHERE e.name = ?",
+                "Employee 5"
+        );
+
+        bh.consume(res);
     }
 
     /**

modules/indexing/src/main/java/org/apache/ignite/internal/processors/query/h2/sql/GridSqlQuerySplitter.java

@@ -718,7 +718,7 @@ private void doPushDownQueryModelRange(SplitterQueryModel model, int begin, int
         pushDownSelectColumns(tblAliases, cols, wrapAlias, select);
 
         // Move all the related WHERE conditions to wrap query.
-        pushDownWhereConditions(tblAliases, cols, wrapAlias, select);
+        pushDownWhereConditions(tblAliases, cols, wrapAlias, select, model, begin, end);
 
         // Push down to a subquery all the JOIN elements and process ON conditions.
         pushDownJoins(tblAliases, cols, model, begin, end, wrapAlias);
@@ -1048,6 +1048,46 @@ private static String uniquePushDownColumnAlias(String uniqueTblAlias, String co
         return uniqueTblAlias + "__" + colName;
     }
 
+    /**
+     * Return table aliases whose WHERE conditions are safe to push down.
+     * For LEFT OUTER JOIN, only aliases from the left branch are safe.
+     */
+    private static Set<GridSqlAlias> tblAliasesToPushdownConditions(
+            SplitterQueryModel model,
+            int begin,
+            int end,
+            Set<GridSqlAlias> tblAliases
+    ) {
+        int leftBranchEnd = -1;
+
+        for (int i = 1; i <= end; i++) {
+            if (model.findJoin(i).isLeftOuter()) {
+                leftBranchEnd = i - 1;
+                break;
+            }
+        }
+
+        if (leftBranchEnd == -1)
+            return tblAliases;
+
+        Set<GridSqlAlias> aliases = U.newIdentityHashSet();
+
+        int safeEnd = Math.min(end, leftBranchEnd);
+
+        if (begin > safeEnd)
+            return aliases;
+
+        for (int i = begin; i <= safeEnd; i++) {
+            GridSqlAlias uniqueTblAlias = model.childModel(i).uniqueAlias();
+
+            assert uniqueTblAlias != null : model.ast().getSQL();
+
+            aliases.add(uniqueTblAlias);
+        }
+
+        return aliases;
+    }
+
     /**
      * @param tblAliases Table aliases for push down.
      * @param cols Columns with generated aliases.
@@ -1058,11 +1098,17 @@ private void pushDownWhereConditions(
         Set<GridSqlAlias> tblAliases,
         Map<String, GridSqlAlias> cols,
         GridSqlAlias wrapAlias,
-        GridSqlSelect select
+        GridSqlSelect select,
+        SplitterQueryModel model,
+        int begin,
+        int end
     ) {
         if (select.where() == null)
             return;
 
+        Set<GridSqlAlias> tblAliasesToPushdownConditions =
+                tblAliasesToPushdownConditions(model, begin, end, tblAliases);
+
         GridSqlSelect wrapSelect = GridSqlAlias.<GridSqlSubquery>unwrap(wrapAlias).subquery();
 
         List<SplitterAndCondition> andConditions = new ArrayList<>();
@@ -1073,7 +1119,7 @@ private void pushDownWhereConditions(
             SplitterAndCondition c = andConditions.get(i);
             GridSqlAst condition = c.ast();
 
-            if (isAllRelatedToTables(tblAliases, U.newIdentityHashSet(), condition)) {
+            if (isAllRelatedToTables(tblAliasesToPushdownConditions, U.newIdentityHashSet(), condition)) {
                 if (!SplitterUtils.isTrue(condition)) {
                     // Replace the original condition with `true` and move it to the wrap query.
                     c.parent().child(c.childIndex(), TRUE);

modules/indexing/src/test/java/org/apache/ignite/internal/processors/query/IgniteSqlSplitterSelfTest.java

@@ -2047,6 +2047,66 @@ public void testAvgVariousDataTypes() throws Exception {
         }
     }
 
+    /**
+     * Verifies LEFT JOIN behavior when the left side is a subquery with DISTINCT and
+     * the result is filtered by a condition on the right table.
+     * The test checks that no rows are returned when there is no matching department name.
+     *
+     * @throws Exception If failed.
+     */
+    @Test
+    public void testLeftJoinWithSubquery() throws Exception {
+        IgniteCache<?, ?> cache = ignite(0).getOrCreateCache(
+                cacheConfig("psLeftJoinSubquery", true, Integer.class, Person.class)
+        );
+
+        String personTbl = "PERSON_LEFT_JOIN_SUBQUERY";
+        String depTbl = "DEPARTMENT_LEFT_JOIN_SUBQUERY";
+
+        try {
+            cache.query(new SqlFieldsQuery(
+                    "CREATE TABLE " + personTbl + " (" +
+                            "id INT PRIMARY KEY, " +
+                            "depId INT, " +
+                            "name VARCHAR" +
+                            ')'
+            )).getAll();
+
+            cache.query(new SqlFieldsQuery(
+                    "CREATE TABLE " + depTbl + " (" +
+                            "id INT PRIMARY KEY, " +
+                            "name VARCHAR" +
+                            ')'
+            )).getAll();
+
+            cache.query(new SqlFieldsQuery(
+                    "INSERT INTO " + personTbl + "(id, depId, name) VALUES (1, 1, 'Emma')"
+            )).getAll();
+
+            cache.query(new SqlFieldsQuery(
+                    "INSERT INTO " + depTbl + "(id, name) VALUES (2, 'TX')"
+            )).getAll();
+
+            List<List<?>> res = cache.query(new SqlFieldsQuery(
+                    "SELECT p.id AS person_id, p.name AS person_name, o.id AS department_id " +
+                            "FROM (SELECT DISTINCT * FROM " + personTbl + ") p " +
+                            "LEFT JOIN " + depTbl + " o ON p.depId = o.id " +
+                            "WHERE o.name = 'SQL'"
+            )).getAll();
+
+            assertTrue(res.isEmpty());
+        }
+        finally {
+            try {
+                cache.query(new SqlFieldsQuery("DROP TABLE IF EXISTS " + personTbl)).getAll();
+                cache.query(new SqlFieldsQuery("DROP TABLE IF EXISTS " + depTbl)).getAll();
+            }
+            finally {
+                cache.destroy();
+            }
+        }
+    }
+
     /**
      * Check avg() with various data types.
      *