[SQLite] Discussion: how to handle duplicate column names in result set?

src/workerd/api/sql-test.js

@@ -504,6 +504,41 @@ async function test(storage) {
     assert.equal(getI(), 2);
   }
 
+  // Test joining two tables with overlapping names
+  {
+    sql.exec(`CREATE TABLE abc (a INT, b INT, c INT);`)
+    sql.exec(`CREATE TABLE cde (c INT, d INT, e INT);`)
+    sql.exec(`INSERT INTO abc VALUES (1,2,3),(4,5,6);`)
+    sql.exec(`INSERT INTO cde VALUES (7,8,9),(1,2,3);`)
+
+    const stmt = sql.prepare(`SELECT * FROM abc, cde`)
+
+    // In normal iteration, data is lost
+    const objResults = Array.from(stmt())
+    assert.equal(Object.values(objResults[0]).length, 5) // duplicate column 'c' dropped
+    assert.equal(Object.values(objResults[1]).length, 5) // duplicate column 'c' dropped
+    assert.equal(Object.values(objResults[2]).length, 5) // duplicate column 'c' dropped
+    assert.equal(Object.values(objResults[3]).length, 5) // duplicate column 'c' dropped
+
+    assert.equal(objResults[0].c, 7) // Value of 'c' is the second in the join
+    assert.equal(objResults[1].c, 1) // Value of 'c' is the second in the join
+    assert.equal(objResults[2].c, 7) // Value of 'c' is the second in the join
+    assert.equal(objResults[3].c, 1) // Value of 'c' is the second in the join
+
+    // Iterator has a 'columnNames' property, with .raw() that lets us get the full data
+    const iterator = stmt();
+    assert.deepEqual(iterator.columnNames, ["a","b","c","c","d","e"])
+    const rawResults = Array.from(iterator.raw())
+    assert.equal(rawResults.length, 4)
+    assert.deepEqual(rawResults[0], [1,2,3,7,8,9])
+    assert.deepEqual(rawResults[1], [1,2,3,1,2,3])
+    assert.deepEqual(rawResults[2], [4,5,6,7,8,9])
+    assert.deepEqual(rawResults[3], [4,5,6,1,2,3])
+
+    // Once an iterator is consumed, it can no longer access the columnNames.
+    assert.deepEqual(iterator.columnNames, [])
+  }
+
   await scheduler.wait(1);
 
   // Test for bug where a cursor constructed from a prepared statement didn't have a strong ref

src/workerd/api/sql.c++

@@ -118,6 +118,17 @@ jsg::Ref<SqlStorage::Cursor::RawIterator> SqlStorage::Cursor::raw(jsg::Lock&) {
   return jsg::alloc<RawIterator>(JSG_THIS);
 }
 
+kj::Array<jsg::V8Ref<v8::String>> SqlStorage::Cursor::getColumnNames(jsg::Lock& js) {
+  KJ_IF_MAYBE(s, state) {
+    cachedColumnNames.ensureInitialized(js, (*s)->query);
+    return KJ_MAP(name, this->cachedColumnNames.get()) {
+      return name.addRef(js);
+    };
+  } else {
+    return kj::Array<jsg::V8Ref<v8::String>>();
+  }
+}
+
 kj::Maybe<kj::Array<SqlStorage::Cursor::Value>> SqlStorage::Cursor::rawIteratorNext(
     jsg::Lock& js, jsg::Ref<Cursor>& obj) {
   return iteratorImpl(js, obj,

src/workerd/api/sql.h

@@ -97,11 +97,14 @@ class SqlStorage::Cursor final: public jsg::Object {
         cachedColumnNames(cachedColumnNames) {}
   ~Cursor() noexcept(false);
 
+  kj::Array<jsg::V8Ref<v8::String>> getColumnNames(jsg::Lock& js);
   JSG_RESOURCE_TYPE(Cursor, CompatibilityFlags::Reader flags) {
     JSG_ITERABLE(rows);
     JSG_METHOD(raw);
+    JSG_READONLY_PROTOTYPE_PROPERTY(columnNames, getColumnNames);
   }
 
+
   using Value = kj::Maybe<kj::OneOf<kj::Array<byte>, kj::StringPtr, double>>;
   // One value returned from SQL. Note that we intentionally return StringPtr instead of String
   // because we know that the underlying buffer returned by SQLite will be valid long enough to be