我知道之前也曾问过类似的问题，并且我检查了大多数问题。但我无法使该查询正常工作。我有几列具有空值，我想在html表中将它们显示为零。但我无法获得想要的结果。
我进行的查询是这样：
$query = "SELECT Id, IFNULL(D0c,0), IFNULL(D1c,0), IFNULL(D2c,0), IFNULL(D3c,0) AS D0c, D1c, D2c, D3c FROM Findata Order by Id Desc Limit 100";
运行查询时，我得到以下结果：
['889', , 1, 4, ],['888', , 1, 2, ],['887', 1, 1, 3, 1],['886', 2, 2, 1, 2],['885', , 1, 2, ], etc
显示零结果，而不是零。请给我一点帮助。谢谢。
-- phpMyAdmin SQL Dump
-- version 4.6.4
-- https://www.phpmyadmin.net/
--
-- Host: 127.0.0.1
-- Generation Time: Jul 06, 2018 at 11:35 PM
-- Server version: 5.7.14
-- PHP Version: 5.6.25
SET SQL_MODE = "NO_AUTO_VALUE_ON_ZERO";
SET time_zone = "+00:00";
/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8mb4 */;
--
-- Database: `Nexel`
--
-- --------------------------------------------------------
--
-- Table structure for table `temptable`
--
CREATE TABLE `temptable` (
`D0c` varchar(5) DEFAULT NULL,
`D1c` varchar(5) DEFAULT NULL,
`D2c` varchar(5) DEFAULT NULL,
`D3c` varchar(5) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
--
-- Dumping data for table `temptable`
--
INSERT INTO `temptable` (`D0c`, `D1c`, `D2c`, `D3c`) VALUES
('1', '2', '1', '1'),
('2', '1', '', '2'),
('2', '2', '1', ''),
('2', '2', '1', ''),
('1', '', '4', ''),
('', '2', '1', '2'),
('3', '', '1', '1'),
('', '2', '2', '1'),
('3', '1', '1', ''),
('2', '1', '', '2'),
('2', '2', '1', ''),
('1', '3', '1', ''),
('2', '', '2', '1'),
('', '2', '3', ''),
('1', '3', '1', ''),
('1', '2', '1', '1'),
('1', '3', '1', ''),
('2', '1', '2', ''),
('', '1', '2', '2'),
('1', '1', '2', '1'),
('1', '2', '1', '1'),
('3', '1', '', '1'),
('2', '2', '', '1'),
('2', '2', '1', ''),
('1', '', '4', ''),
('1', '4', '', ''),
('', '2', '', '3'),
('1', '', '3', '1'),
('2', '1', '2', ''),
('1', '2', '1', '1'),
('', '3', '1', '1'),
('2', '2', '1', ''),
('2', '1', '1', '1'),
('2', '1', '2', ''),
('2', '1', '2', ''),
('', '2', '1', '2'),
('', '1', '3', '1'),
('2', '1', '2', ''),
('', '1', '4', '');
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
答案 0 :(得分：1)
请参阅下面的更新
尝试使用COALESCE（）代替IFNULL：
SELECT
Id,
COALESCE(D0c,0) AS `FixedD0c`,
COALESCE(D1c,0) AS `FixedD1c`,
COALESCE(D2c,0) AS `FixedD2c`,
COALESCE(D3c,0) AS `FixedD3c`,
D0c,
D1c,
D2c,
D3c
FROM Findata
Order by Id Desc
Limit 100;
注意：顺便说一句，在您的问题所示的查询中，您似乎试图一次全部分配列别名，但您只是重命名了第4列的结果，然后将其包括在内第2-4列，但不包含IFNULL。您从查询中获得的结果将不会与您的问题中显示的一样，但是输出中将有7列。
编辑：
MySQL 5.6模式设置：
CREATE TABLE `Findata` (
`D0c` varchar(5) DEFAULT NULL,
`D1c` varchar(5) DEFAULT NULL,
`D2c` varchar(5) DEFAULT NULL,
`D3c` varchar(5) DEFAULT NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;
--
-- Dumping data for table `temptable`
--
INSERT INTO `Findata` (`D0c`, `D1c`, `D2c`, `D3c`) VALUES
('1', '2', '1', '1'),
('2', '1', NULL, '2'),
('2', '2', '1', NULL),
('2', '2', '1', NULL),
('1', NULL, '4', NULL),
(NULL, '2', '1', '2'),
('3', NULL, '1', '1'),
(NULL, '2', '2', '1'),
('3', '1', '1', NULL),
('2', '1', NULL, '2'),
('2', '2', '1', NULL),
('1', '3', '1', NULL),
('2', NULL, '2', '1'),
(NULL, '2', '3', NULL),
('1', '3', '1', NULL),
('1', '2', '1', '1'),
('1', '3', '1', NULL),
('2', '1', '2', NULL),
(NULL, '1', '2', '2'),
('1', '1', '2', '1'),
('1', '2', '1', '1'),
('3', '1', NULL, '1'),
('2', '2', NULL, '1'),
('2', '2', '1', NULL),
('1', NULL, '4', NULL),
('1', '4', NULL, NULL),
(NULL, '2', NULL, '3'),
('1', NULL, '3', '1'),
('2', '1', '2', NULL),
('1', '2', '1', '1'),
(NULL, '3', '1', '1'),
('2', '2', '1', NULL),
('2', '1', '1', '1'),
('2', '1', '2', NULL),
('2', '1', '2', NULL),
(NULL, '2', '1', '2'),
(NULL, '1', '3', '1'),
('2', '1', '2', NULL),
(NULL, '1', '4', NULL);
查询1 ：
SELECT
COALESCE(D0c,0) AS `FixedD0c`,
COALESCE(D1c,0) AS `FixedD1c`,
COALESCE(D2c,0) AS `FixedD2c`,
COALESCE(D3c,0) AS `FixedD3c`,
D0c,
D1c,
D2c,
D3c
FROM Findata
Limit 100
Results ：
| FixedD0c | FixedD1c | FixedD2c | FixedD3c | D0c | D1c | D2c | D3c |
|----------|----------|----------|----------|--------|--------|--------|--------|
| 1 | 2 | 1 | 1 | 1 | 2 | 1 | 1 |
| 2 | 1 | 0 | 2 | 2 | 1 | (null) | 2 |
| 2 | 2 | 1 | 0 | 2 | 2 | 1 | (null) |
| 2 | 2 | 1 | 0 | 2 | 2 | 1 | (null) |
| 1 | 0 | 4 | 0 | 1 | (null) | 4 | (null) |
| 0 | 2 | 1 | 2 | (null) | 2 | 1 | 2 |
| 3 | 0 | 1 | 1 | 3 | (null) | 1 | 1 |
| 0 | 2 | 2 | 1 | (null) | 2 | 2 | 1 |
| 3 | 1 | 1 | 0 | 3 | 1 | 1 | (null) |
| 2 | 1 | 0 | 2 | 2 | 1 | (null) | 2 |
| 2 | 2 | 1 | 0 | 2 | 2 | 1 | (null) |
| 1 | 3 | 1 | 0 | 1 | 3 | 1 | (null) |
| 2 | 0 | 2 | 1 | 2 | (null) | 2 | 1 |
| 0 | 2 | 3 | 0 | (null) | 2 | 3 | (null) |
| 1 | 3 | 1 | 0 | 1 | 3 | 1 | (null) |
| 1 | 2 | 1 | 1 | 1 | 2 | 1 | 1 |
| 1 | 3 | 1 | 0 | 1 | 3 | 1 | (null) |
| 2 | 1 | 2 | 0 | 2 | 1 | 2 | (null) |
| 0 | 1 | 2 | 2 | (null) | 1 | 2 | 2 |
| 1 | 1 | 2 | 1 | 1 | 1 | 2 | 1 |
| 1 | 2 | 1 | 1 | 1 | 2 | 1 | 1 |
| 3 | 1 | 0 | 1 | 3 | 1 | (null) | 1 |
| 2 | 2 | 0 | 1 | 2 | 2 | (null) | 1 |
| 2 | 2 | 1 | 0 | 2 | 2 | 1 | (null) |
| 1 | 0 | 4 | 0 | 1 | (null) | 4 | (null) |
| 1 | 4 | 0 | 0 | 1 | 4 | (null) | (null) |
| 0 | 2 | 0 | 3 | (null) | 2 | (null) | 3 |
| 1 | 0 | 3 | 1 | 1 | (null) | 3 | 1 |
| 2 | 1 | 2 | 0 | 2 | 1 | 2 | (null) |
| 1 | 2 | 1 | 1 | 1 | 2 | 1 | 1 |
| 0 | 3 | 1 | 1 | (null) | 3 | 1 | 1 |
| 2 | 2 | 1 | 0 | 2 | 2 | 1 | (null) |
| 2 | 1 | 1 | 1 | 2 | 1 | 1 | 1 |
| 2 | 1 | 2 | 0 | 2 | 1 | 2 | (null) |
| 2 | 1 | 2 | 0 | 2 | 1 | 2 | (null) |
| 0 | 2 | 1 | 2 | (null) | 2 | 1 | 2 |
| 0 | 1 | 3 | 1 | (null) | 1 | 3 | 1 |
| 2 | 1 | 2 | 0 | 2 | 1 | 2 | (null) |
| 0 | 1 | 4 | 0 | (null) | 1 | 4 | (null) |
答案 1 :(得分：0)
代替
IFNULL(D0c,0)
尝试
REPLACE(Doc,NULL,0)
答案 2 :(得分：0)
如果为空字符串：
$query = "SELECT Id, CASE when D0c like '' then '0' else D0c end as D0c, CASE when D1c like '' then '0' else D1c end as D1c, CASE when D2c like '' then '0' else D2c end as D2c, case when D3c like '' then '0' else D3c end as D3c FROM Mytable Order by Id Desc Limit 100" ;