Question

我有两张桌子：

CREATE TABLE IF NOT EXISTS `tools` (
  `pk_id` int(11) NOT NULL AUTO_INCREMENT,
  `id` int(11) NOT NULL,
  `title` varchar(13) DEFAULT NULL,
  PRIMARY KEY (`pk_id`));

CREATE TABLE IF NOT EXISTS `features` (
  `pk_id` int(11) NOT NULL AUTO_INCREMENT,
  `id` int(11) NOT NULL,
  `feature` varchar(13) DEFAULT NULL,
  `number` int(11),
  PRIMARY KEY (`pk_id`),
  FOREIGN KEY (id) REFERENCES tools(id));

然后我有脚本（见下文）来获得这样的东西：

Tools  Feature1 Feature2 Feature3 Feature4
=========================================
ToolA  1        0        0        1
ToolB  0        0        1        0

当我在行1中添加number而不是MAX(IF(pa1.feature = "', feature,'", "', number, '", "', 0, '"))时，脚本运行正常。否则它表示此行存在一些错误。为什么以及如何解决它？

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(IF(pa1.feature = "', feature,'", "', number, '", "', 0, '")) AS ', REPLACE(feature, ' ', '')
    )
  ) INTO @sql
FROM features;

SET @sql = CONCAT('SELECT p.id
                    , p.title
                    , ', @sql, ' 
                   FROM tools p
                   LEFT JOIN features AS pa1 
                    ON p.id = pa1.id
                   GROUP BY p.id');

SELECT concat('SQL: ', @sql);

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

更新

这是由上述脚本创建的原始SQL语句，其中包含一些错误：

SELECT p.id \ n，p.title \ n，MAX（IF（pa1.feature = \＆＃34; feature 68 \＆＃34;，\＆＃34; 6 \＆＃34;，\ ＆＃34; 0 \＆＃34;））AS   feature68，MAX（IF（pa1.feature = \＆＃34; feature 68 \＆＃34;，\＆＃34; 7 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature68，MAX（IF（pa1.feature = \＆＃34; feature 68 \＆＃34;，\＆＃34; 1 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature68，MAX（IF（pa1.feature = \＆＃34; feature 172 \＆＃34;，\＆＃34; 2 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature172，MAX（IF（pa1.feature = \＆＃34; feature 56 \＆＃34;，\＆＃34; 1 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature56，MAX（IF（pa1.feature = \＆＃34; feature 193 \＆＃34;，\＆＃34; 4 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature193，MAX（IF（pa1.feature = \＆＃34; feature 71 \＆＃34;，\＆＃34; 3 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature71，MAX（IF（pa1.feature = \＆＃34; feature 201 \＆＃34;，\＆＃34; 2 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature201，MAX（IF（pa1.feature = \＆＃34; feature 80 \＆＃34;，\＆＃34; 2 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature80，MAX（IF（pa1.feature = \＆＃34; feature 203 \＆＃34;，\＆＃34; 5 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature203，MAX（IF（pa1.feature = \＆＃34; feature 82 \＆＃34;，\＆＃34; 8 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature82，MAX（IF（pa1.feature = \＆＃34; feature 80 \＆＃34;，\＆＃34; 9 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature80，MAX（IF（pa1.feature = \＆＃34; feature 82 \＆＃34;，\＆＃34; 9 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature82，MAX（IF（pa1.feature = \＆＃34; feature 201 \＆＃34;，\＆＃34; 5 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature201，MAX（IF（pa1.feature = \＆＃34; feature 80 \＆＃34;，\＆＃34; 15 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature80，MAX（IF（pa1.feature = \＆＃34; feature 56 \＆＃34;，\＆＃34; 3 \＆＃34;，\＆＃34; 0 \＆＃34;））AS   feature56，MAX（I \ n FROM tools p \ n
  LEFT JOIN功能AS pa1 \ n ON p.id = pa1.id \ n
  GROUP BY p.id

正如我所说，如果我用number替换1，那么相同的代码也可以。

Answer 1

我发现您发布的代码存在两个问题。

在sql字符串中通常使用单引号而不是双引号指定。我不是100％使用mysql，因此该平台可能允许您拥有此处的代码。
查看最后一个字段MAX(I \n FROM tools这显然是错误的。

这可能是两件事之一。 @SQL是小的，或者数字列中有空。如果问题是你有一个null，那么这将修复将在你的select语句中使用它。

FROM features
WHERE number is not null;

用于合并两个表并将行转换为列的SQL脚本

1 个答案: