diff --git a/src/test/kotlin/kestrel/WindowFunctionTest.kt b/src/test/kotlin/kestrel/WindowFunctionTest.kt
new file mode 100644
index 0000000..4f9a8a6
--- /dev/null
+++ b/src/test/kotlin/kestrel/WindowFunctionTest.kt
@@ -0,0 +1,153 @@
+package kestrel
+
+import kestrel.catalog.Catalog
+import kestrel.engine.ExplainResult
+import kestrel.engine.Executor
+import kestrel.engine.SelectResult
+import kestrel.engine.StatementResult
+import kestrel.sql.lexer.Lexer
+import kestrel.sql.parser.Parser
+import kestrel.storage.Value
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class WindowFunctionTest {
+    private val catalog = Catalog()
+    private val executor = Executor(catalog)
+
+    private fun run(sql: String): List<StatementResult> =
+        Parser(Lexer(sql).tokenize()).parseProgram().map { executor.execute(it) }
+
+    private fun select(sql: String): SelectResult = run(sql).single() as SelectResult
+
+    private fun explain(sql: String): List<String> = (run(sql).single() as ExplainResult).plan
+
+    private fun text(value: String) = Value.TextValue(value)
+    private fun int(value: Long) = Value.IntegerValue(value)
+
+    /**
+     * eng (deptId 1): ada/linus tie at 400 (ada inserted first), grace at 300.
+     * sales (deptId 2): sam/kay tie at 200 (sam inserted first), meg at 100.
+     * Salaries also happen to be in strict descending order by id across the whole table, which
+     * keeps the no-PARTITION-BY tests below easy to eyeball.
+     */
+    private fun seed() {
+        run("CREATE TABLE departments (id INTEGER PRIMARY KEY, name TEXT NOT NULL)")
+        run("CREATE TABLE employees (id INTEGER PRIMARY KEY, deptId INTEGER, name TEXT, salary INTEGER)")
+        run("INSERT INTO departments VALUES (1, 'eng'), (2, 'sales')")
+        run(
+            "INSERT INTO employees VALUES " +
+                "(1, 1, 'ada', 400), (2, 1, 'linus', 400), (3, 1, 'grace', 300), " +
+                "(4, 2, 'sam', 200), (5, 2, 'kay', 200), (6, 2, 'meg', 100)"
+        )
+    }
+
+    @Test
+    fun rowNumberAssignsSequentialNumbersWithinEachPartition() {
+        seed()
+        val result = select(
+            "SELECT id, ROW_NUMBER() OVER (PARTITION BY deptId ORDER BY salary DESC) AS rn " +
+                "FROM employees ORDER BY id ASC"
+        )
+        assertEquals(
+            listOf(
+                listOf(int(1), int(1)), listOf(int(2), int(2)), listOf(int(3), int(3)),
+                listOf(int(4), int(1)), listOf(int(5), int(2)), listOf(int(6), int(3))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun rowNumberWithoutOverOrderByFallsBackToPartitionArrivalOrder() {
+        seed()
+        val result = select("SELECT id, ROW_NUMBER() OVER (PARTITION BY deptId) AS rn FROM employees ORDER BY id ASC")
+        assertEquals(
+            listOf(
+                listOf(int(1), int(1)), listOf(int(2), int(2)), listOf(int(3), int(3)),
+                listOf(int(4), int(1)), listOf(int(5), int(2)), listOf(int(6), int(3))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun rankLeavesGapsAfterTiesButDenseRankDoesNot() {
+        seed()
+        val result = select(
+            "SELECT id, RANK() OVER (PARTITION BY deptId ORDER BY salary DESC) AS r, " +
+                "DENSE_RANK() OVER (PARTITION BY deptId ORDER BY salary DESC) AS dr " +
+                "FROM employees ORDER BY id ASC"
+        )
+        assertEquals(
+            listOf(
+                listOf(int(1), int(1), int(1)),
+                listOf(int(2), int(1), int(1)),
+                listOf(int(3), int(3), int(2)),
+                listOf(int(4), int(1), int(1)),
+                listOf(int(5), int(1), int(1)),
+                listOf(int(6), int(3), int(2))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun rankWithoutPartitionOrdersTheWholeResultSet() {
+        seed()
+        val result = select("SELECT id, RANK() OVER (ORDER BY salary DESC) AS r FROM employees ORDER BY id ASC")
+        assertEquals(
+            listOf(
+                listOf(int(1), int(1)), listOf(int(2), int(1)), listOf(int(3), int(3)),
+                listOf(int(4), int(4)), listOf(int(5), int(4)), listOf(int(6), int(6))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun aggregateWindowWithoutOrderByRepeatsTheWholePartitionTotalOnEveryRow() {
+        seed()
+        val result = select(
+            "SELECT id, SUM(salary) OVER (PARTITION BY deptId) AS deptTotal FROM employees ORDER BY id ASC"
+        )
+        assertEquals(
+            listOf(
+                listOf(int(1), int(1100)), listOf(int(2), int(1100)), listOf(int(3), int(1100)),
+                listOf(int(4), int(500)), listOf(int(5), int(500)), listOf(int(6), int(500))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun aggregateWindowWithOrderByRunsCumulativelyAndTiesSharePeerGroupTotal() {
+        seed()
+        val result = select(
+            "SELECT id, SUM(salary) OVER (PARTITION BY deptId ORDER BY salary DESC) AS running " +
+                "FROM employees ORDER BY id ASC"
+        )
+        assertEquals(
+            listOf(
+                listOf(int(1), int(800)), listOf(int(2), int(800)), listOf(int(3), int(1100)),
+                listOf(int(4), int(400)), listOf(int(5), int(400)), listOf(int(6), int(500))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun aggregateWindowWithUniqueOrderKeyProducesARunningTotal() {
+        seed()
+        val result = select("SELECT id, SUM(salary) OVER (ORDER BY id) AS running FROM employees ORDER BY id ASC")
+        assertEquals(
+            listOf(
+                listOf(int(1), int(400)), listOf(int(2), int(800)), listOf(int(3), int(1100)),
+                listOf(int(4), int(1300)), listOf(int(5), int(1500)), listOf(int(6), int(1600))
+            ),
+            result.rows
+        )
+    }
+