diff --git a/src/test/kotlin/kestrel/store/sql/DiskExecutorTest.kt b/src/test/kotlin/kestrel/store/sql/DiskExecutorTest.kt
index 6fb03cb..eb59d84 100644
--- a/src/test/kotlin/kestrel/store/sql/DiskExecutorTest.kt
+++ b/src/test/kotlin/kestrel/store/sql/DiskExecutorTest.kt
@@ -1113,3 +1113,160 @@ class DiskExecutorTest {
         assertEquals(2, db.select("SELECT * FROM registrations").rows.size)
     }
 
+    @Test
+    fun createUniqueCompositeIndexAllowsMultipleRowsWithANullInEitherColumn() {
+        val db = newDatabase()
+        db.run("CREATE TABLE registrations (event_id INTEGER, user_id INTEGER)")
+        db.run("CREATE UNIQUE INDEX idx_reg ON registrations(event_id, user_id)")
+        db.run("INSERT INTO registrations VALUES (1, NULL), (1, NULL), (NULL, 100), (NULL, 100)")
+        assertEquals(4, db.select("SELECT * FROM registrations").rows.size)
+    }
+
+    @Test
+    fun createUniqueCompositeIndexOverExistingDuplicateCombinationsFailsAndLeavesNoTraceOfTheIndex() {
+        val db = newDatabase()
+        db.run("CREATE TABLE registrations (event_id INTEGER, user_id INTEGER)")
+        db.run("INSERT INTO registrations VALUES (1, 100), (1, 100)")
+        assertFailsWith<DiskTableException> { db.run("CREATE UNIQUE INDEX idx_reg ON registrations(event_id, user_id)") }
+        assertTrue(db.catalog.table("registrations").secondaryIndexes.isEmpty())
+    }
+
+    @Test
+    fun createUniqueCompositeIndexRejectsAnUpdateThatWouldDuplicateAnotherRowsCombination() {
+        val db = newDatabase()
+        db.run("CREATE TABLE registrations (id INTEGER PRIMARY KEY, event_id INTEGER, user_id INTEGER)")
+        db.run("CREATE UNIQUE INDEX idx_reg ON registrations(event_id, user_id)")
+        db.run("INSERT INTO registrations VALUES (1, 1, 100), (2, 1, 200)")
+        assertFailsWith<DiskTableException> { db.run("UPDATE registrations SET user_id = 100 WHERE id = 2") }
+        assertEquals(int(200), db.select("SELECT user_id FROM registrations WHERE id = 2").rows.single().single())
+    }
+
+    @Test
+    fun createUniqueCompositeIndexDataAndConstraintSurviveClosingAndReopeningTheCatalog() {
+        val db = newDatabase()
+        db.run("CREATE TABLE registrations (event_id INTEGER, user_id INTEGER)")
+        db.run("CREATE UNIQUE INDEX idx_reg ON registrations(event_id, user_id)")
+        db.run("INSERT INTO registrations VALUES (1, 100)")
+        db.reopen()
+        assertFailsWith<DiskTableException> { db.run("INSERT INTO registrations VALUES (1, 100)") }
+        val handle = db.catalog.table("registrations").secondaryIndexes.single()
+        assertEquals(listOf("event_id", "user_id"), handle.columnNames)
+        assertTrue(handle.unique)
+    }
+
+    // --- index pushdown: proven by DiskTable's access counters, not just by correct results,
+    // since a full scan and an index lookup return identical rows for these queries.
+
+    @Test
+    fun whereEqualityOnThePrimaryKeyUsesAPointLookupNotAFullScan() {
+        val db = newDatabase()
+        db.seedUsers()
+        val table = db.catalog.table("users")
+        val result = db.select("SELECT name FROM users WHERE id = 2")
+        assertEquals(listOf(listOf(text("linus"))), result.rows)
+        assertEquals(1, table.pointLookupCount)
+        assertEquals(0, table.scanCount)
+    }
+
+    @Test
+    fun aMissingPrimaryKeyPointLookupReturnsNoRowsWithoutScanning() {
+        val db = newDatabase()
+        db.seedUsers()
+        val table = db.catalog.table("users")
+        val result = db.select("SELECT name FROM users WHERE id = 999")
+        assertEquals(emptyList<List<Value>>(), result.rows)
+        assertEquals(1, table.pointLookupCount)
+        assertEquals(0, table.scanCount)
+    }
+
+    @Test
+    fun aRangeOnThePrimaryKeyUsesARangeScanNotAFullScan() {
+        val db = newDatabase()
+        db.seedUsers()
+        val table = db.catalog.table("users")
+        val result = db.select("SELECT name FROM users WHERE id > 1 AND id <= 3 ORDER BY id")
+        assertEquals(listOf(listOf(text("linus")), listOf(text("grace"))), result.rows)
+        assertEquals(1, table.rangeScanCount)
+        assertEquals(0, table.scanCount)
+    }
+
+    @Test
+    fun equalityOnAnUnindexedColumnStillFallsBackToAFullScan() {
+        val db = newDatabase()
+        db.seedUsers()
+        val table = db.catalog.table("users")
+        val result = db.select("SELECT id FROM users WHERE name = 'linus'")
+        assertEquals(listOf(listOf(int(2))), result.rows)
+        assertEquals(1, table.scanCount)
+        assertEquals(0, table.pointLookupCount)
+    }
+
+    @Test
+    fun equalityOnASecondaryIndexedColumnUsesTheSecondaryIndexNotAFullScan() {
+        val db = newDatabase()
+        db.seedUsers()
+        db.run("CREATE INDEX idx_age ON users(age)")
+        val table = db.catalog.table("users")
+        val scansBeforeSelect = table.scanCount // backfilling the new index already scanned once
+        val result = db.select("SELECT name FROM users WHERE age = 54")
+        assertEquals(listOf(listOf(text("linus"))), result.rows)
+        assertEquals(1, table.secondaryLookupCount)
+        assertEquals(scansBeforeSelect, table.scanCount)
+    }
+
+    @Test
+    fun equalityOnAllColumnsOfACompositeSecondaryIndexUsesTheSecondaryIndexNotAFullScan() {
+        val db = newDatabase()
+        db.run("CREATE TABLE users (id INTEGER PRIMARY KEY, age INTEGER, name TEXT)")
+        db.run("INSERT INTO users VALUES (1, 36, 'ada'), (2, 36, 'grace')")
+        db.run("CREATE INDEX idx_both ON users(age, name)")
+        val table = db.catalog.table("users")
+        val scansBeforeSelect = table.scanCount // backfilling the new index already scanned once
+        val result = db.select("SELECT id FROM users WHERE age = 36 AND name = 'grace'")
+        assertEquals(listOf(listOf(int(2))), result.rows)
+        assertEquals(1, table.secondaryLookupCount)
+        assertEquals(scansBeforeSelect, table.scanCount)
+    }
+
+    @Test
+    fun equalityOnOnlyOneColumnOfACompositeSecondaryIndexFallsBackToAFullScan() {
+        val db = newDatabase()
+        db.run("CREATE TABLE users (id INTEGER PRIMARY KEY, age INTEGER, name TEXT)")
+        db.run("INSERT INTO users VALUES (1, 36, 'ada'), (2, 36, 'grace')")
+        db.run("CREATE INDEX idx_both ON users(age, name)")
+        val table = db.catalog.table("users")
+        val scansBeforeSelect = table.scanCount
+        val result = db.select("SELECT id FROM users WHERE age = 36")
+        assertEquals(2, result.rows.size)
+        assertEquals(0, table.secondaryLookupCount)
+        assertEquals(scansBeforeSelect + 1, table.scanCount)
+    }
+
+    @Test
+    fun aRangeOnASingleColumnSecondaryIndexUsesARangeScanNotAFullScan() {
+        val db = newDatabase()
+        db.seedUsers()
+        db.run("CREATE INDEX idx_age ON users(age)")
+        val table = db.catalog.table("users")
+        val scansBeforeSelect = table.scanCount // backfilling the new index already scanned once
+        val result = db.select("SELECT name FROM users WHERE age > 40 AND age <= 85 ORDER BY age")
+        assertEquals(listOf(listOf(text("linus")), listOf(text("grace"))), result.rows)
+        assertEquals(1, table.rangeScanCount)
+        assertEquals(0, table.secondaryLookupCount)
+        assertEquals(scansBeforeSelect, table.scanCount)
+    }
+
+    @Test
+    fun aRangeOnTheFirstColumnOfACompositeSecondaryIndexUsesARangeScanNotAFullScan() {
+        val db = newDatabase()
+        db.run("CREATE TABLE order_lines (order_id INTEGER, line_no INTEGER, sku TEXT)")
+        db.run("INSERT INTO order_lines VALUES (1, 1, 'apple'), (2, 1, 'kiwi'), (3, 1, 'mango')")
+        db.run("CREATE INDEX idx_order_sku ON order_lines(order_id, sku)")
+        val table = db.catalog.table("order_lines")
+        val scansBeforeSelect = table.scanCount // backfilling the new index already scanned once
+        val result = db.select("SELECT sku FROM order_lines WHERE order_id > 1 ORDER BY order_id")
+        assertEquals(listOf(listOf(text("kiwi")), listOf(text("mango"))), result.rows)
+        assertEquals(1, table.rangeScanCount)
+        assertEquals(scansBeforeSelect, table.scanCount)
+    }
+