From c5676edd5e7c7d8ea540249e57735c8b4d9cb518 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E9=AB=98=E9=93=81?= <szujobs@gmail.com>
Date: Tue, 3 Oct 2017 14:34:40 -0500
Subject: [PATCH] Updated Druid_SQL_AST (markdown)

---
 Druid_SQL_AST.md | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/Druid_SQL_AST.md b/Druid_SQL_AST.md
index def5d9b..88bbee0 100644
--- a/Druid_SQL_AST.md
+++ b/Druid_SQL_AST.md
@@ -15,7 +15,7 @@ class SQLSelect extends SQLObject {}
 class SQLSelectQueryBlock extends SQLObject {}
 ```
 
-## 2.1 常用的SQLExpr有哪些
+## 2.1. 常用的SQLExpr有哪些
 ```java
 package com.alibaba.druid.sql.ast.expr;
 
@@ -40,7 +40,7 @@ class SQLBinaryOpExpr implements SQLExpr {
 }
 ```
 
-## 2.2 常用的SQLStatemment
+## 2.2. 常用的SQLStatemment
 最常用的Statement当然是SELECT/UPDATE/DELETE/INSERT，他们分别是
 ```java
 package com.alibaba.druid.sql.ast.statement;
@@ -64,24 +64,32 @@ class SQLInsertStatement implements SQLStatement {
 }
 ```
 
-## 2.3 SQLTableSource
+## 2.3. SQLTableSource
 ```java
 class SQLTableSourceImpl extends SQLObjectImpl implements SQLTableSource { 
     String alias;
 }
 
-// select * from emp where i = 3，这里的from emp是一个SQLExprTableSource
+// 例如 select * from emp where i = 3，这里的from emp是一个SQLExprTableSource
 // 其中expr是一个name=emp的SQLIdentifierExpr
 class SQLExprTableSource extends SQLTableSourceImpl {
     SQLExpr expr;
 }
 
+// 例如 select * from emp e inner join org o on e.org_id = o.id
+// 其中left 'emp e' 是一个SQLExprTableSource，right 'org o'也是一个SQLExprTableSource
+// condition 'e.org_id = o.id'是一个SQLBinaryOpExpr
 class SQLJoinTableSource extends SQLTableSourceImpl {
     SQLTableSource left;
     SQLTableSource right;
     JoinType joinType; // INNER_JOIN/CROSS_JOIN/LEFT_OUTER_JOIN/RIGHT_OUTER_JOIN/...
     SQLExpr condition;
 }
+
+// 例如 select * from (select * from temp) a，这里第一层from(...)是一个SQLSubqueryTableSource
+SQLSubqueryTableSource extends SQLTableSourceImpl {
+    SQLSelect select;
+}
 ```