Question

我不确定如何提出这个问题，但现在就去了。

如果我有这样的查询：

SELECT `locations`.`location_name` AS 'Location', `inventory`.`equip_model` AS 'Model', count( `inventory`.`equip_model` ) AS 'Count'
FROM mod_inventory_data AS `inventory`
LEFT JOIN mod_locations_data AS `locations` ON `locations`.location_id = `inventory`.location_id
WHERE inventory.equip_model LIKE '%iPad%'
GROUP BY Location, Model

返回如下结果：

Location        Model                    Count
------------------------------------------------
Bannach         iPad                     7
Bannach         iPad 2                   1
Ben Franklin    iPad                     3
Ben Franklin    iPad 2                   1
Ben Franklin    iPad 64 gb               3
Ben Franklin    iPad2 64GB               1
Jefferson       iPad                     4
Jefferson       Ipad 216 gb wi-fi        6
Jefferson       iPad2 64GB               2
Kennedy         iPad                     2
Kennedy         iPad 2 WIFI 16GB Black   1
Madison         iPad                     3
Madison         iPad 2                   6
McKinley        iPad                     4
McKinley        iPad 2                   2
McKinley        iPad 2 MC769LL/A         6
McKinley        iPad 64 gb               1

有没有办法替换重复的位置名称，所以它看起来像这样：

Location        Model                    Count
------------------------------------------------
Bannach         iPad                     7
NULL            iPad 2                   1
Ben Franklin    iPad                     3
NULL            iPad 2                   1
NULL            iPad 64 gb               3
NULL            iPad2 64GB               1
Jefferson       iPad                     4
NULL            Ipad 216 gb wi-fi        6
NULL            iPad2 64GB               2
Kennedy         iPad                     2
NULL            iPad 2 WIFI 16GB Black   1
Madison         iPad                     3
NULL            iPad 2                   6
McKinley        iPad                     4
NULL            iPad 2                   2
NULL            iPad 2 MC769LL/A         6
NULL            iPad 64 gb               1

基本上我希望位置名称仅显示在找到的第一个实例上，暗示之后的任何null都是针对该位置的。

希望我说得对...

Answer 1

SELECT Location, Model, Count
FROM (
    SELECT IF(Location = @PrevLocation, NULL, Location) AS Location,
           Model, Count, @PrevLocation := Location
    FROM (<your query>) AS subq
    CROSS JOIN (SELECT @PrevLocation := NULL) AS init
    ) AS subq2

MySql设置名称为NULL

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