MySQL使用通配符检查与组重复？

    +----+--------------+-----+-----------+----------+
    | ID | NAME         | AGE | ADDRESS   | SALARY   |
    +----+--------------+-----+-----------+----------+
    |  1 | Ramesh Olive |  32 | Ahmedabad |  2000.00 |
    |  2 | Tan Kau      |  25 | Delhi     |  1500.00 |
    |  3 | Jason Tan Kau|  25 | Delhi     |  2000.00 |
    |  4 | Chaitali     |  25 | Mumbai    |  6500.00 |
    |  5 | Hardik       |  27 | Bhopal    |  8500.00 |
    |  6 | Hardik Jass  |  27 | Bhopal    |  4500.00 |
    |  7 | Muffy John   |  24 | Indore    | 10000.00 |
    |  8 | Muffy Lee    |  24 | Indore    | 10000.00 |
    +----+--------------+-----+-----------+----------+

在上面的例子中,假设表名是“table_a”和
1)“Tan Kau”与“Jason Tan Kau”重复,2)“Hardik”与“Hardik Jass”重复

如何编写将产生如下输出的SQL？

我认为这会奏效,但应该很慢.有什么想法来改善这个吗？

Select A.*, IF(B.ID IS NULL, "", "DUP") as DUP
FROM table_a A 
LEFT JOIN table_a B 
ON A.NAME LIKE CONCATE("%", B.NAME, "%") AND A.ID != B.ID


    +----+--------------+-----+-----------+----------+-----+
    | ID | NAME         | AGE | ADDRESS   | SALARY   | DUP |
    +----+--------------+-----+-----------+----------+-----+
    |  1 | Ramesh Olive |  32 | Ahmedabad |  2000.00 |     |
    |  2 | Tan Kau      |  25 | Delhi     |  1500.00 | Dup |
    |  3 | Jason Tan Kau|  25 | Delhi     |  2000.00 | Dup |
    |  4 | Chaitali     |  25 | Mumbai    |  6500.00 |     |
    |  5 | Hardik       |  27 | Bhopal    |  8500.00 | Dup |
    |  6 | Hardik Jass  |  27 | Bhopal    |  4500.00 | Dup | 
    |  7 | Muffy John   |  24 | Indore    | 10000.00 |     |
    |  8 | Muffy Lee    |  24 | Indore    | 10000.00 |     |
    +----+--------------+-----+-----------+----------+-----+

解决方法:

您的查询可以通过添加反向条件返回预期结果：

SELECT A.*, IF(B.ID IS NULL, "", "DUP") as DUP
FROM persons A 
LEFT JOIN persons B 
ON a.ID <> b.ID 
AND (a.Name LIKE CONCAT ("%", b.Name, "%") OR b.Name LIKE CONCAT ("%", a.Name, "%"))
ORDER BY ID;

我不知道它是否会更快,但另一种方法是使用INSTR：

SELECT A.*, IF(B.ID IS NULL, "", "DUP") as DUP
FROM persons A 
LEFT JOIN persons B 
ON a.ID <> b.ID 
AND (Instr(a.Name, b.Name) > 0 OR Instr(b.Name, a.Name) > 0)
ORDER BY ID;

SQL Fiddle

标签：mysql,group-by,duplication
来源： https://codeday.me/bug/20190806/1594640.html