diff --git a/Src/Asp.Net/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs b/Src/Asp.Net/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs
index 5b03fb18f..11d2e1739 100644
--- a/Src/Asp.Net/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs
+++ b/Src/Asp.Net/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs
@@ -61,6 +61,10 @@ namespace SqlSugar
             {
                 return (HasWhere?"AND":"WHERE")+ " ROWNUM=1";
             }
+            else if (this.Context is PostgreSQLExpressionContext)
+            {
+                return "limit 1";
+            }
             else
             {
                 return "limit 0,1";
diff --git a/Src/Asp.Net/SqlSugar/Infrastructure/Mapper.cs b/Src/Asp.Net/SqlSugar/Infrastructure/Mapper.cs
index 2de6f1526..9f6f2b96e 100644
--- a/Src/Asp.Net/SqlSugar/Infrastructure/Mapper.cs
+++ b/Src/Asp.Net/SqlSugar/Infrastructure/Mapper.cs
@@ -103,6 +103,10 @@ namespace SqlSugar
                 }
             }
             result = queryBuilder.GetSelectByItems(selectItems);
+            if (_context.CurrentConnectionConfig.DbType == DbType.PostgreSQL)
+            {
+                result = result.ToLower();
+            }
             return result;
         }
     }
diff --git a/Src/Asp.Net/SqlSugar/OnlyNet/PostgreSQLExpressionContext.cs b/Src/Asp.Net/SqlSugar/OnlyNet/PostgreSQLExpressionContext.cs
new file mode 100644
index 000000000..38cad7d5a
--- /dev/null
+++ b/Src/Asp.Net/SqlSugar/OnlyNet/PostgreSQLExpressionContext.cs
@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace SqlSugar
+{
+    internal class PostgreSQLExpressionContext : ExpressionContext, ILambdaExpressions
+    {
+        public SqlSugarClient Context
+        {
+            get
+            {
+                throw new NotImplementedException();
+            }
+
+            set
+            {
+                throw new NotImplementedException();
+            }
+        }
+    }
+}
diff --git a/Src/Asp.Net/SqlSugar/SqlSugar.csproj b/Src/Asp.Net/SqlSugar/SqlSugar.csproj
index 68d6b9a0e..f3803275c 100644
--- a/Src/Asp.Net/SqlSugar/SqlSugar.csproj
+++ b/Src/Asp.Net/SqlSugar/SqlSugar.csproj
@@ -115,6 +115,7 @@
     <Compile Include="ExternalServiceInterface\ISerializeService.cs" />
     <Compile Include="Entities\DefaultServices.cs" />
     <Compile Include="Infrastructure\Mapper.cs" />
+    <Compile Include="OnlyNet\PostgreSQLExpressionContext.cs" />
     <Compile Include="Realization\Oracle\Deleteable\OracleDeleteable.cs" />
     <Compile Include="Realization\Oracle\Insertable\OracleInsertable.cs" />
     <Compile Include="Realization\Oracle\Updateable\OracleUpdateable.cs" />
diff --git a/Src/Asp.NetCore2/SqlSeverTest/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs b/Src/Asp.NetCore2/SqlSeverTest/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs
index 5b03fb18f..11d2e1739 100644
--- a/Src/Asp.NetCore2/SqlSeverTest/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs
+++ b/Src/Asp.NetCore2/SqlSeverTest/SqlSugar/ExpressionsToSql/Subquery/Items/SubTop.cs
@@ -61,6 +61,10 @@ namespace SqlSugar
             {
                 return (HasWhere?"AND":"WHERE")+ " ROWNUM=1";
             }
+            else if (this.Context is PostgreSQLExpressionContext)
+            {
+                return "limit 1";
+            }
             else
             {
                 return "limit 0,1";