Update common-Extractor.md

Author: jxnu-liguobin

docs/lab/smt/common-Extractor.md

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+---
+toc: content
+nav:
+  path: /lab/smt
+---
+
+# common - Extractor
+
+- `Extractor` 迭代`ResultSet`并封装为样例类的集合。
+- 默认提供22个`GenericRowN`实例，即支持22个列的select，允许拓展。
+- 支持自定义类型映射函数。
+
+## 使用
+```scala
+
+    val statement = DriverManager
+      .getConnection(
+        "jdbc:h2:mem:zim?caseSensitive=false;MODE=MYSQL;TRACE_LEVEL_FILE=2;INIT=RUNSCRIPT FROM 'classpath:test.sql'"
+      )
+      .createStatement()
+    statement.execute(s"""select * from T_USER""".stripMargin)
+
+    val rowSet: ResultSet = statement.getResultSet
+
+    // default type mapping
+    val rows = Extractor[GenericRow4[Int, String, String, String]].from(rowSet) 
+    // 再也不用到处写 `while(rowSet.next) { }` 了
+```
+
+## 优化
+```scala
+  import org.bitlap.common.jdbc._
+  
+  implicit lazy val conn = DriverManager.getConnection(
+    "jdbc:h2:mem:zim?caseSensitive=false;MODE=MYSQL;TRACE_LEVEL_FILE=2;INIT=RUNSCRIPT FROM 'classpath:test.sql'"
+  )
+  val ret1 = Extractor[GenericRow4[Int, String, String, String]].from(sql"select * from T_USER")
+```