Update mysql AddDefaultValue

Src/Asp.Net/SqlSugar/Realization/MySql/DbMaintenance/MySqlDbMaintenance.cs

@@ -560,10 +560,10 @@ namespace SqlSugar
             {
                 defaultValue = "";
             }
-            if (defaultValue.ToLower().IsIn("now()", "current_timestamp") || defaultValue.ToLower().Contains("current_timestamp"))
+            if (defaultValue.ToLower().IsIn("now()", "current_timestamp","null") || defaultValue.ToLower().Contains("current_timestamp")|| defaultValue.Contains("()"))
             {
                 string template = "ALTER table {0} CHANGE COLUMN {1} {1} {3} {4} default {2} COMMENT '{5}'";
-                var dbColumnInfo = this.Context.DbMaintenance.GetColumnInfosByTableName(tableName).First(it => it.DbColumnName.Equals(columnName, StringComparison.CurrentCultureIgnoreCase));
+                var dbColumnInfo = this.Context.DbMaintenance.GetColumnInfosByTableName(tableName,false).First(it => it.DbColumnName.Equals(columnName, StringComparison.CurrentCultureIgnoreCase));
                 var value = Regex.Match(defaultValue, @"\(\d\)$").Value;
                 string sql = string.Format(template, tableName, columnName, defaultValue, dbColumnInfo.DataType + value, dbColumnInfo.IsNullable ? " NULL " : " NOT NULL ", dbColumnInfo.ColumnDescription);
                 this.Context.Ado.ExecuteCommand(sql);

Src/Asp.NetCore2/SqlSugar/Realization/MySql/DbMaintenance/MySqlDbMaintenance.cs

@@ -561,10 +561,10 @@ namespace SqlSugar
             {
                 defaultValue = "";
             }
-            if (defaultValue.ToLower().IsIn("now()", "current_timestamp") || defaultValue.ToLower().Contains("current_timestamp"))
+            if (defaultValue.ToLower().IsIn("null","now()", "current_timestamp") || defaultValue.ToLower().Contains("current_timestamp")|| defaultValue.Contains("()"))
             {
                 string template = "ALTER table {0} CHANGE COLUMN {1} {1} {3} {4} default {2} COMMENT '{5}'";
-                var dbColumnInfo = this.Context.DbMaintenance.GetColumnInfosByTableName(tableName).First(it => it.DbColumnName.Equals(columnName, StringComparison.CurrentCultureIgnoreCase));
+                var dbColumnInfo = this.Context.DbMaintenance.GetColumnInfosByTableName(tableName,false).First(it => it.DbColumnName.Equals(columnName, StringComparison.CurrentCultureIgnoreCase));
                 var value = Regex.Match(defaultValue, @"\(\d\)$").Value;
                 string sql = string.Format(template, tableName, columnName, defaultValue, dbColumnInfo.DataType + value, dbColumnInfo.IsNullable ? " NULL " : " NOT NULL ", dbColumnInfo.ColumnDescription);
                 this.Context.Ado.ExecuteCommand(sql);