mysql 關於命令行下，字符串間少逗號分隔符的坑
阿新 • • 發佈：2018-03-30
concat 字符串連接 mysql 字符串 坑 遇到一個 mysql 的坑，關於字符串連接的問題，分享一下
mysql> select * from my_table; +----+--------+------------+ | id | mod_id | mod_name | +----+--------+------------+ | 1 | 20 | red | | 2 | 20 | blue | | 3 | 20 | pink | | 4 | 21 | yellow | | 5 | 21 | green | | 6 | 21 | white | | 7 | 21 | black | | 8 | 30 | gray | | 9 | 30 | purple | | 10 | 30 | pinkpurple | | 11 | 30 | red purple | +----+--------+------------+ 11 rows in set (0.00 sec)
原始表數據。
mysql> select * from my_table where mod_name in ("red", ‘blue‘, ‘pink‘, ‘purple‘); +----+--------+----------+ | id | mod_id | mod_name | +----+--------+----------+ | 1 | 20 | red | | 2 | 20 | blue | | 3 | 20 | pink | | 9 | 30 | purple | +----+--------+----------+ 4 rows in set (0.00 sec)
使用 where 條件查詢匹配列表中的列。（正常查詢）
mysql> select * from my_table where mod_name in ("red", ‘blue‘, ‘pink‘ ‘purple‘); +----+--------+------------+ | id | mod_id | mod_name | +----+--------+------------+ | 1 | 20 | red | | 2 | 20 | blue | | 10 | 30 | pinkpurple | +----+--------+------------+ 3 rows in set (0.00 sec)
註意最後一組值，(‘pink‘ ‘purple‘) 中間少了個逗號，那麽查詢出來的結果，默認會解釋為 ‘pinkpurple‘ 字符串。
mysql> select * from my_table where mod_name = (‘pink‘ ‘purple‘);
+----+--------+------------+
| id | mod_id | mod_name |
+----+--------+------------+
| 10 | 30 | pinkpurple |
+----+--------+------------+
1 row in set (0.00 sec)
使用 = 符號條件精確查詢，仍然解釋為 兩個字符串的連接結果。
mysql> select * from my_table where mod_name = ‘pink‘ ‘purple‘;
+----+--------+------------+
| id | mod_id | mod_name |
+----+--------+------------+
| 10 | 30 | pinkpurple |
+----+--------+------------+
1 row in set (0.00 sec)
使用 = 符號條件精確查詢，取消掉括弧，仍然解釋為 兩個字符串的連接結果。
mysql> select * from my_table where mod_name = ‘‘ ‘purple‘;
+----+--------+----------+
| id | mod_id | mod_name |
+----+--------+----------+
| 9 | 30 | purple |
+----+--------+----------+
1 row in set (0.00 sec)
頭一個字符串為0長度字符串，那麽合並即等於 purple 字符串。
mysql> select * from my_table where mod_name = ‘red‘‘ ‘ ‘purple‘;
Empty set (0.00 sec)
寫三個字符串，其中第一個字符串的單引號和第二個字符串的單引號中間沒有空格，那麽解釋為未知字符。。。。。
mysql> select * from my_table where mod_name = ‘red‘ ‘ ‘ ‘purple‘;
+----+--------+------------+
| id | mod_id | mod_name |
+----+--------+------------+
| 11 | 30 | red purple |
+----+--------+------------+
1 row in set (0.00 sec)
‘red‘ ‘ ‘ ‘purple‘ ，每一組字符串用空格隔開，那麽就合並為 red purple 字符串。本來，這應該報語法錯誤的，但是，，，，，
唉，被坑了，，，，
mysql 關於命令行下，字符串間少逗號分隔符的坑