优化ISqlString接口的Having方法

Dapper.LiteSql/Dapper.LiteSql/SqlString/SqlString.cs

@@ -382,7 +382,14 @@ namespace Dapper.LiteSql
         /// <param name="args">参数(支持多个参数或者把多个参数放在一个匿名对象中)</param>
         public ISqlString Having(string sql, params object[] args)
         {
-            return Append("having " + sql, args);
+            if (RemoveSubSqls(_sql.ToString()).Contains("having"))
+            {
+                return Append("and " + sql, args);
+            }
+            else
+            {
+                return Append("having " + sql, args);
+            }
         }
 
         /// <summary>
@@ -392,7 +399,14 @@ namespace Dapper.LiteSql
         /// <param name="args">参数(支持多个参数或者把多个参数放在一个匿名对象中)</param>
         public ISqlQueryable<T> Having<T>(string sql, params object[] args) where T : new()
         {
-            return Append<T>("having " + sql, args);
+            if (RemoveSubSqls(_sql.ToString()).Contains("having"))
+            {
+                return Append<T>("and " + sql, args);
+            }
+            else
+            {
+                return Append<T>("having " + sql, args);
+            }
         }
         #endregion