第二部分字符串函數
1. ASCII('str'): 返回字符串 str 中最左邊字符的 ASCII 代碼值。
2. BIN(N): 返回十進制數值 N 的二進制數值的字符串表現形式。
3. BIT_LENGTH(str): 返回字符串 str 所占的位長度。
4. CHAR(N,... [USING charset_name]): 會將每一個參數 N 都解釋為整數，返回由這些整數在 ASCII 碼中所對應字符所組成的字符串。
5. CHAR_LENGTH(str): 單純返回 str 的字符串長度;
6. CONV(N,from_base,to_base): 將數值在不同進制間轉換。
7. COMPRESS():壓縮(不推薦使用 CHAR 或VARCHAR 來存儲壓縮字符串。最好使用一個 BLOB 列代替);
8. UNCOMOPRESS(): 解壓內容
壓縮實例:
MariaDB[study_db]> SELECT
-> LENGTH(REPEAT('a', 50)),
-> LENGTH(COMPRESS(REPEAT('a',50))),
-> COMPRESS(REPEAT('a',50)),
-> UNCOMPRESS(COMPRESS(REPEAT('a',50)));
+-------------------------+----------------------------------+--------------------------+----------------------------------------------------+
| LENGTH(REPEAT('a', 50)) | LENGTH(COMPRESS(REPEAT('a',50))) | COMPRESS(REPEAT('a',50)) | UNCOMPRESS(COMPRESS(REPEAT('a',50))) ??????????????|
+-------------------------+----------------------------------+--------------------------+----------------------------------------------------+
| ?????????????????????50 | ??????????????????????????????16 | 2 ??x?KL$ ??\? ???????????| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |
+-------------------------+----------------------------------+--------------------------+----------------------------------------------------+
1 row in set (0.00 sec)
2.2大小寫UPPER()與LOWER()
MariaDB[study_db]> select book_name, book_author_name FROM new_books;
+------------------+---------------------------+
|book_name|book_author_name|
+------------------+---------------------------+
|跟我學MariaDB|hhw|
|跟我學NodeJS|hhw|
|HTTP權威指南|O'Reilly|
|追風箏的人|Khaled Hosseini|
MariaDB [study_db]> select UPPER(book_name),LOWER( book_author_name) FROM new_books;
+------------------+---------------------------+
|UPPER(book_name)|LOWER( book_author_name)|
+------------------+---------------------------+
|跟我學MARIADB|hhw|
|跟我學NODEJS|hhw|
|HTTP權威指南|o'reilly|
|追風箏的人|khaled hosseini|
|小王子|antoine marie jean-b|
