--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/SQLHandler.h	Wed Dec 07 00:41:11 2022 +0100
@@ -0,0 +1,120 @@
+/**
+ * Relational pipes
+ * Copyright © 2022 František Kučera (Frantovo.cz, GlobalCode.info)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, version 3 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+#include <memory>
+#include <string>
+#include <vector>
+#include <iostream>
+#include <sstream>
+#include <locale>
+#include <codecvt>
+
+#include <relpipe/reader/typedefs.h>
+#include <relpipe/reader/TypeId.h>
+#include <relpipe/reader/handlers/RelationalReaderStringHandler.h>
+#include <relpipe/reader/handlers/AttributeMetadata.h>
+
+#include "Configuration.h"
+#include "RelpipeSQLWriterException.h"
+
+namespace relpipe {
+namespace out {
+namespace sql {
+
+using namespace relpipe;
+using namespace relpipe::reader;
+using namespace relpipe::reader::handlers;
+
+class SQLHandler : public RelationalReaderStringHandler {
+private:
+	std::ostream& output;
+	Configuration& configuration;
+	const char QUOTE = '"';
+	std::wstring_convert<std::codecvt_utf8<wchar_t>> convertor; // generate SQL always in UTF-8
+	std::vector<AttributeMetadata> firstAttributes;
+	integer_t valueCount = 0;
+
+	/**
+	 * @param a
+	 * @param b
+	 * @return true if relations have same number and types of attributes (names may differ)
+	 */
+	bool matches(const std::vector<AttributeMetadata>& a, const std::vector<AttributeMetadata>& b) {
+		if (a.size() != b.size()) return false;
+		for (int i = 0, limit = a.size(); i < limit; i++) if (a[i].getTypeId() != b[i].getTypeId()) return false;
+		return true;
+	}
+public:
+
+	SQLHandler(std::ostream& output, Configuration& configuration) : output(output), configuration(configuration) {
+	}
+
+	void startRelation(string_t name, std::vector<AttributeMetadata> attributes) override {
+		// TODO: CREATE TABLE
+		// TODO: escape identifiers
+		// TODO: ALTER TABLE / add columns on duplicate relation name
+		// TODO: custom data type mapping
+		// TODO: custom name transformation
+		// TODO: custom SQL script before/after stream/relation/record
+		// TODO: comments and/or custom comments
+		// TODO: optional transactions: BEGIN/COMMIT/ROLLBACK for stream/relation/record
+		output << "CREATE TABLE " << convertor.to_bytes(name) << " ( ... );" << std::endl;
+		
+		if (firstAttributes.empty()) {
+			firstAttributes = attributes;
+			if (configuration.writeHeader) for (auto attr : attributes) attribute(configuration.writeTypes ? attr.getAttributeName() + L"::" + attr.getTypeName() : attr.getAttributeName());
+		} else if (matches(firstAttributes, attributes)) {
+			// do UNION ALL – just append the records
+		} else {
+			// throw RelpipeSQLWriterException(L"To the SQL format we can convert only one relation or multiple relations that have same number of attributes of same types (relation and attribute names may differ – result is named after the first one).");
+		}
+	}
+
+	void attribute(const string_t& value) override {
+		valueCount++;
+		
+		if (value.size() > 0) {
+			output << QUOTE;
+			for (auto ch : convertor.to_bytes(value)) {
+				if (ch == QUOTE) output << QUOTE << QUOTE;
+				else output << ch;
+			}
+			output << QUOTE;
+		}
+
+		if (valueCount % firstAttributes.size()) {
+			output << ",";
+		} else {
+			// TODO: INSERT INTO ...
+			// TODO: escape identifiers and values
+			// TODO: optional use of function/procedure instead of INSERT
+			// TODO: optional INSERT of multiple records
+			output << std::endl << "INSERT INTO ... VALUES ... ;" << std::endl;;
+			valueCount = 0;
+		}
+	}
+
+	void endOfPipe() {
+		output.flush();
+	}
+
+};
+
+}
+}
+}