LibSQL: Partially implement the UPDATE command

This implements enough to update rows filtered by a WHERE clause.

Userland/Libraries/LibSQL/AST/Update.cpp

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2022, Tim Flynn <trflynn89@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibSQL/AST/AST.h>
+#include <LibSQL/Database.h>
+#include <LibSQL/Meta.h>
+#include <LibSQL/Row.h>
+
+namespace SQL::AST {
+
+ResultOr<ResultSet> Update::execute(ExecutionContext& context) const
+{
+    auto const& schema_name = m_qualified_table_name->schema_name();
+    auto const& table_name = m_qualified_table_name->table_name();
+    auto table_def = TRY(context.database->get_table(schema_name, table_name));
+
+    Vector<Row> matched_rows;
+
+    for (auto& table_row : TRY(context.database->select_all(*table_def))) {
+        context.current_row = &table_row;
+
+        if (auto const& where_clause = this->where_clause()) {
+            auto where_result = TRY(where_clause->evaluate(context)).to_bool();
+            if (!where_result.has_value() || !where_result.value())
+                continue;
+        }
+
+        TRY(matched_rows.try_append(move(table_row)));
+    }
+
+    ResultSet result { SQLCommand::Update };
+
+    for (auto& update_column : m_update_columns) {
+        auto row_value = TRY(update_column.expression->evaluate(context));
+
+        for (auto& table_row : matched_rows) {
+            auto& row_descriptor = *table_row.descriptor();
+
+            for (auto const& column_name : update_column.column_names) {
+                if (!table_row.has(column_name))
+                    return Result { SQLCommand::Update, SQLErrorCode::ColumnDoesNotExist, column_name };
+
+                auto column_index = row_descriptor.find_if([&](auto element) { return element.name == column_name; }).index();
+                auto column_type = row_descriptor[column_index].type;
+
+                if (!row_value.is_type_compatible_with(column_type))
+                    return Result { SQLCommand::Update, SQLErrorCode::InvalidValueType, column_name };
+
+                table_row[column_index] = row_value;
+            }
+
+            TRY(context.database->update(table_row));
+            result.insert_row(table_row, {});
+        }
+    }
+
+    return result;
+}
+
+}