public int Selectstring production int condition DateTimePicker StartTime DateTimePicker EndTime string sql = $select count from ProductProductionRe

存在语法错误。应该将DateTimePicker的值转换为字符串，并在SQL语句中使用单引号将其括起来，如下所示：

string sql = $@"select count(*) from {ProductProductionRecorderTableMainName}{production} where {ProductionData} >= '{StartTime.Value.ToString("yyyy-MM-dd HH:mm:ss")}' and {ProductionData} <= '{EndTime.Value.ToString("yyyy-MM-dd HH:mm:ss")}' and {ProductionCondition} = {condition} ";