在使用mysql进行搜索时，如何忽略大小写之间的差异

在使用mysql进行搜索时，如何忽略大小写之间的差异？请执行以下操作：

SELECT user 
FROM users 
WHERE UPPER( user ) = UPPER( 'moustafa' );

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基本上，您将结果转换为一个大小写，并与同样转换为大写的搜索词进行比较，实际上忽略了大小写。

通常，您应该使用WHERE upper（COLUMNNAME）=upper（'valuetocompare'）

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或者，您可以使用WHERE-UPPER（COLUMNNAME），比如UPPER（“%valuetocompare%”），如果您想进行子字符串搜索，您可以将数据以小写形式存储在mySQL中，只需对其执行查询。

可以使用

UPPER

和

lower

函数，但是，您也可以通过选择适当的排序规则和/或列类型来影响大小写敏感度

例如，

latin1\u general\u cs

对

VARCHAR

和

VARBINARY

都区分大小写：

DROP TABLE IF EXISTS `case_sensitive`;
CREATE TABLE `case_sensitive` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `nonbinary` VARCHAR(255),
    `binary`  VARBINARY(255),
    PRIMARY KEY (`id`)
) ENGINE=InnoDB COLLATE latin1_general_cs;

INSERT INTO `case_sensitive` (`nonbinary`, `binary`) VALUES ('A', 'A');

SELECT * FROM `case_sensitive` WHERE `nonbinary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+
1 row in set (0.00 sec)

SELECT * FROM `case_sensitive` WHERE `binary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+
1 row in set (0.00 sec)

SELECT * FROM `case_sensitive` WHERE `nonbinary` = 'a';

Empty set (0.00 sec)

SELECT * FROM `case_sensitive` WHERE `binary` = 'a';

Empty set (0.00 sec)

DROP TABLE IF EXISTS `case_insensitive`;
CREATE TABLE `case_insensitive` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `nonbinary` VARCHAR(255),
    `binary`  VARBINARY(255),
    PRIMARY KEY (`id`)
) ENGINE=InnoDB COLLATE latin1_general_ci;

INSERT INTO `case_insensitive` (`nonbinary`, `binary`) VALUES ('A', 'A');

SELECT * FROM `case_insensitive` WHERE `nonbinary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+
1 row in set (0.00 sec)

SELECT * FROM `case_insensitive` WHERE `binary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+

SELECT * FROM `case_insensitive` WHERE `nonbinary` = 'a';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+

SELECT * FROM `case_insensitive` WHERE `binary` = 'a';

Empty set (0.00 sec)

而

latin1\u general\u ci

对

VARCHAR

不区分大小写，对

VARBINARY

区分大小写：

DROP TABLE IF EXISTS `case_sensitive`;
CREATE TABLE `case_sensitive` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `nonbinary` VARCHAR(255),
    `binary`  VARBINARY(255),
    PRIMARY KEY (`id`)
) ENGINE=InnoDB COLLATE latin1_general_cs;

INSERT INTO `case_sensitive` (`nonbinary`, `binary`) VALUES ('A', 'A');

SELECT * FROM `case_sensitive` WHERE `nonbinary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+
1 row in set (0.00 sec)

SELECT * FROM `case_sensitive` WHERE `binary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+
1 row in set (0.00 sec)

SELECT * FROM `case_sensitive` WHERE `nonbinary` = 'a';

Empty set (0.00 sec)

SELECT * FROM `case_sensitive` WHERE `binary` = 'a';

Empty set (0.00 sec)

DROP TABLE IF EXISTS `case_insensitive`;
CREATE TABLE `case_insensitive` (
    `id` INT NOT NULL AUTO_INCREMENT,
    `nonbinary` VARCHAR(255),
    `binary`  VARBINARY(255),
    PRIMARY KEY (`id`)
) ENGINE=InnoDB COLLATE latin1_general_ci;

INSERT INTO `case_insensitive` (`nonbinary`, `binary`) VALUES ('A', 'A');

SELECT * FROM `case_insensitive` WHERE `nonbinary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+
1 row in set (0.00 sec)

SELECT * FROM `case_insensitive` WHERE `binary` = 'A';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+

SELECT * FROM `case_insensitive` WHERE `nonbinary` = 'a';

+----+-----------+--------+
| id | nonbinary | binary |
+----+-----------+--------+
|  1 | A         | A      |
+----+-----------+--------+

SELECT * FROM `case_insensitive` WHERE `binary` = 'a';

Empty set (0.00 sec)

因此，您应该选择最适合您需要的排序规则和列类型。您可以在此处找到更多信息：

字符串搜索中的大小写敏感度

MySQL中的字符集和排序规则

MySQL支持的字符集和排序规则

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我在搜索的列上使用utf8\u unicode\uCI-不区分大小写的collate…并且它可以工作

+1：将求值的两边都按相同的大小写（大写或小写）将提供不区分大小写的搜索。警告：如果存在索引，在列上使用函数将不会使用索引。仅复制粘贴代码是不够的，您必须解释它的作用和方式。

SELECT * FROM table_name WHERE column_name1 LIKE '%A%' OR column_name1 LIKE '%a%';