From 4e00ace631c06215629f7fdc1fe324502a119530 Mon Sep 17 00:00:00 2001
From: wenshao <szujobs@hotmail.com>
Date: Tue, 18 Apr 2017 17:08:07 +0800
Subject: [PATCH] add method PageUtils.hasUnorderedLimit for mysql. for issue
 #1688

---
 .../com/alibaba/druid/sql/PagerUtils.java     | 32 +++++++++++++++++++
 .../sql/PagerUtilsTest_hasUnorderedLimit.java | 24 ++++++++++++++
 2 files changed, 56 insertions(+)
 create mode 100644 src/test/java/com/alibaba/druid/bvt/sql/PagerUtilsTest_hasUnorderedLimit.java

diff --git a/src/main/java/com/alibaba/druid/sql/PagerUtils.java b/src/main/java/com/alibaba/druid/sql/PagerUtils.java
index 03a9fa54ce..786dcb006f 100644
--- a/src/main/java/com/alibaba/druid/sql/PagerUtils.java
+++ b/src/main/java/com/alibaba/druid/sql/PagerUtils.java
@@ -16,7 +16,9 @@
 package com.alibaba.druid.sql;
 
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
 
+import com.alibaba.druid.DruidRuntimeException;
 import com.alibaba.druid.sql.ast.SQLExpr;
 import com.alibaba.druid.sql.ast.SQLOrderBy;
 import com.alibaba.druid.sql.ast.SQLOver;
@@ -42,11 +44,13 @@ import com.alibaba.druid.sql.ast.statement.SQLUnionQuery;
 import com.alibaba.druid.sql.dialect.db2.ast.stmt.DB2SelectQueryBlock;
 import com.alibaba.druid.sql.dialect.mysql.ast.statement.MySqlSelectQueryBlock;
 import com.alibaba.druid.sql.ast.SQLLimit;
+import com.alibaba.druid.sql.dialect.mysql.visitor.MySqlASTVisitorAdapter;
 import com.alibaba.druid.sql.dialect.odps.ast.OdpsSelectQueryBlock;
 import com.alibaba.druid.sql.dialect.oracle.ast.stmt.OracleSelectQueryBlock;
 import com.alibaba.druid.sql.dialect.postgresql.ast.stmt.PGSelectQueryBlock;
 import com.alibaba.druid.sql.dialect.sqlserver.ast.SQLServerSelectQueryBlock;
 import com.alibaba.druid.sql.dialect.sqlserver.ast.SQLServerTop;
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
 import com.alibaba.druid.util.JdbcConstants;
 import com.alibaba.druid.util.JdbcUtils;
 
@@ -503,4 +507,32 @@ public class PagerUtils {
         
         return -1;
     }
+
+    public static boolean hasUnorderedLimit(String sql, String dbType) {
+        List<SQLStatement> stmtList = SQLUtils.parseStatements(sql, dbType);
+
+        if (!JdbcConstants.MYSQL.equals(dbType)) {
+            throw new DruidRuntimeException("not supported. dbType : " + dbType);
+        }
+
+        final AtomicInteger unorderedLimitCount = new AtomicInteger();
+        MySqlASTVisitorAdapter visitor = new MySqlASTVisitorAdapter() {
+            @Override
+            public boolean visit(MySqlSelectQueryBlock x) {
+                SQLOrderBy orderBy = x.getOrderBy();
+                SQLLimit limit = x.getLimit();
+
+                if (limit != null && (orderBy == null || orderBy.getItems().size() == 0)) {
+                    unorderedLimitCount.incrementAndGet();
+                }
+                return false;
+            }
+        };
+
+        for (SQLStatement stmt : stmtList) {
+            stmt.accept(visitor);
+        }
+
+        return unorderedLimitCount.get() > 0;
+    }
 }
diff --git a/src/test/java/com/alibaba/druid/bvt/sql/PagerUtilsTest_hasUnorderedLimit.java b/src/test/java/com/alibaba/druid/bvt/sql/PagerUtilsTest_hasUnorderedLimit.java
new file mode 100644
index 0000000000..41d13a2bb7
--- /dev/null
+++ b/src/test/java/com/alibaba/druid/bvt/sql/PagerUtilsTest_hasUnorderedLimit.java
@@ -0,0 +1,24 @@
+package com.alibaba.druid.bvt.sql;
+
+import com.alibaba.druid.sql.PagerUtils;
+import com.alibaba.druid.util.JdbcConstants;
+import junit.framework.TestCase;
+import org.junit.Assert;
+
+public class PagerUtilsTest_hasUnorderedLimit extends TestCase {
+
+    public void test_false() throws Exception {
+        String sql = " select * from test t order by id limit 3";
+        assertFalse(PagerUtils.hasUnorderedLimit(sql, JdbcConstants.MYSQL));
+    }
+
+    public void test_false_1() throws Exception {
+        String sql = " select * from test t";
+        assertFalse(PagerUtils.hasUnorderedLimit(sql, JdbcConstants.MYSQL));
+    }
+
+    public void test_true() throws Exception {
+        String sql = " select * from test t limit 3";
+        assertTrue(PagerUtils.hasUnorderedLimit(sql, JdbcConstants.MYSQL));
+    }
+}