Mybatis plus 多表联查字段名重复处理 Column 'xxxx' in where clause is ambiguous

问题描述

由以下表foo、和bar

foo

bar

-- ----------------------------
-- Table structure for bar
-- ----------------------------
DROP TABLE IF EXISTS `bar`;
CREATE TABLE `bar`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `goods` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL,
  `alias` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of bar
-- ----------------------------
INSERT INTO `bar` VALUES (1, '愉快肥皂', 'ykfz');
INSERT INTO `bar` VALUES (2, '快乐肥宅水', 'klfzs');
INSERT INTO `bar` VALUES (3, '金坷垃', 'jkl');

-- ----------------------------
-- Table structure for foo
-- ----------------------------
DROP TABLE IF EXISTS `foo`;
CREATE TABLE `foo`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `inc` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `alias` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `bar_id` int(11) NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of foo
-- ----------------------------
INSERT INTO `foo` VALUES (1, '天天好', 'tth', 1);
INSERT INTO `foo` VALUES (2, '天天棒', 'ttb', 2);
INSERT INTO `foo` VALUES (3, 'giao', 'g', 3);

SET FOREIGN_KEY_CHECKS = 1;

现在需要关联对这两个表进行关联查询

由于foo和bar中都有id和alias字段，所以需要给他们增加别名，得到查询的SQL语句如下。

SELECT
	foo.id AS id,
	inc,
	foo.alias AS alias,
	goods,
	bar.alias AS goods_alias 
FROM
	foo
	JOIN bar ON foo.bar_id = bar.id;

根据上面的SQL我们可以按照 Mybatis Plus 使用-wrapper-自定义sql

构建一个Mapper和xml

xml

<mapper namespace="com.demo.mapper.FooBarMapper">

    <select id="getPatchItemList" resultType="com.demo.FooBar">
	SELECT
		foo.id AS id,
		inc,
		foo.alias AS alias,
		goods,
		bar.alias AS goods_alias 
	FROM
		foo
		JOIN bar ON foo.bar_id = bar.id;
	${ew.customSqlSegment}
    select>
mapper>

${ew.customSqlSegment} 是Mybatis Plus的动态条件构造器的最终条件SQL

Mapper

public interface FooBarMapper extends BaseMapper<FooBar> {
    List<FooBar> getPatchItemList(
                @Param(Constants.WRAPPER) Wrapper<FooBar> wrapper);
}

但我们执行下面查询语句时

 Wrapper<FooBar> wrapper = Wrappers.<FooBar>lambdaQuery()
                .like(FooBar::getAlias, "b"); // --> alias like '%b%'

List<ProviderDataItem> res =
                       FooBarMapperMapper.getPatchItemList(wrapper);

会报错 Column ‘alias’ in where clause is ambiguous，提示的意义是说这个 alias 字段是不够明确是暧昧的。

原因： 这是由于连表之后字段中alias重复了，查询结果集中含有两个alias不知道是哪一个才是要查询的，条件语句是针对查询结果集的所以字段重命名是无效的。

解决方式

1.使用明确的字段名称 表名.字段名

Wrapper<FooBar> wrapper = Wrappers.<FooBar>Query()
                .like("foo.alias", "b");

2.把查询结果作为子查询，然后在增加条件语句

SELECT
	* 
FROM
	(
	SELECT
		foo.id AS id,
		inc,
		foo.alias AS alias,
		goods,
		bar.alias AS goods_alias 
	FROM
		foo
	JOIN bar ON foo.bar_id = bar.id 
	) AS t ${ew.customSqlSegment}

这种方式就可以直接使用下面方式进行查询而不需要补全表名：

 Wrapper<FooBar> wrapper = Wrappers.<FooBar>lambdaQuery()
                .like(FooBar::getAlias, "b");

该种方式是由我同事告诉我的，：P