MySQL 为什么“_”（下划线）匹配“-”（连字符）？
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Why does "_" (underscore) match "-" (hyphen)?
提问by E.G.
I have to look for a PDF manual using this query:
我必须使用此查询查找 PDF 手册：
root@localhost:test> select * from a where name like '%taz_manual%.pdf%';
+--------------------+------------------+-------------+
| name | description | size |
+--------------------+------------------+-------------+
| taz-manual-1.1.pdf | Manual v1.0 TA-Z | 31351902 |
| taz-manual-0.2.pdf | Manual v1.0 T1-A | 3578278 |
| taz_manual-2.0.pdf | Manual v2.0 GA-X | 542578278 |
etc........
+--------------------+------------------+-------------+
132 row in set (0.00 sec)
Why am I seeing the the one with dashes when I specify the name to be taz_manual%.pdf?
当我指定名称时，为什么会看到带破折号的那个taz_manual%.pdf？
回答by Book Of Zeus
Because the underscore _is a wildcard like the percent %, except that it only looks for one character.
因为下划线_是一个和百分比一样的通配符%，只不过它只查找一个字符。
SQL pattern matching enables you to use "_" to match any single character and "%" to match an arbitrary number of characters (including zero characters).
SQL 模式匹配使您可以使用“_”来匹配任何单个字符，使用“%”来匹配任意数量的字符（包括零个字符）。
(From section 3.3.4.7. Pattern Matchingin the MySQL documentation.)
（来自MySQL 文档中的3.3.4.7. 模式匹配部分。）
If you want to use the underscore in likeas a literal, you have to escape it:
如果要将下划线like用作文字，则必须对其进行转义：
select * from a where name like '%taz\_manual%.pdf%';
回答by NBhat
I had a similar issue with space and hyphens while matching strings with exact match:
在将字符串与完全匹配匹配时，我遇到了类似的空格和连字符问题：
SELECT id FROM location WHERE name = 'IND - HQ';
The above query didn't return any records in MySQL. I had to escape the spaces and hyphens and use LIKEinstead of exact match with equals (=) as follows:
上述查询在 MySQL 中没有返回任何记录。我不得不转义空格和连字符，并使用LIKE等于 (=) 而不是完全匹配，如下所示：
SELECT id FROM location WHERE name LIKE 'IND_\-_HQ';
