feat: 添加原生 FROM 支持。

mybatis-flex-core/src/main/java/com/mybatisflex/core/query/RawQueryTable.java

@@ -0,0 +1,38 @@
+/*
+ *  Copyright (c) 2022-2023, Mybatis-Flex (fuhai999@gmail.com).
+ *  <p>
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *  <p>
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *  <p>
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+package com.mybatisflex.core.query;
+
+import com.mybatisflex.core.dialect.IDialect;
+
+/**
+ * @author 王帅
+ * @since 2023-10-16
+ */
+public class RawQueryTable extends QueryTable {
+
+    private final String content;
+
+    public RawQueryTable(String content) {
+        this.content = content;
+    }
+
+    @Override
+    public String toSql(IDialect dialect) {
+        return this.content;
+    }
+
+}