improve sql parser

src/main/java/com/alibaba/druid/sql/ast/statement/SQLExplainStatement.java

@@ -0,0 +1,29 @@
+package com.alibaba.druid.sql.ast.statement;
+
+import com.alibaba.druid.sql.ast.SQLStatement;
+import com.alibaba.druid.sql.ast.SQLStatementImpl;
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+
+public class SQLExplainStatement extends SQLStatementImpl {
+
+    protected SQLStatement statement;
+
+    public SQLStatement getStatement() {
+        return statement;
+    }
+
+    public void setStatement(SQLStatement statement) {
+        if (statement != null) {
+            statement.setParent(this);
+        }
+        this.statement = statement;
+    }
+
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+        if (visitor.visit(this)) {
+            acceptChild(visitor, statement);
+        }
+        visitor.endVisit(this);
+    }
+}