SQLite的選擇/過濾表並限制

Question

我在做一個項目的SQL學校輸出我有這個表：

name  price_gold price_euros role  universe 
---------- ---------- ----------- ---------- ----------------- 
Sylvanas 10,000  9,99   Specialist World of Warcraft 
The Lost V 10,000  9,99   Specialist The Lost Vikings 
Azmodan  10,000  9,99   Specialist Diablo 
Zagara  7,000  8,49   Specialist Starcraft 
Murky  7,000  8,49   Specialist World of Warcraft 
Abathur  10,000  9,99   Specialist Starcraft 
Gazlowe  4,000  6,49   Specialist World of Warcraft 
Nazeebo  10,000  9,99   Specialist Diablo 
Sgt. Hamme 7,000  8,49   Specialist Starcraft 
Artanis  10,000  9,99   Warrior  Starcraft 
Rexxar  10,000  9,99   Warrior  World of Warcraft 
Leoric  10,000  9,99   Warrior  Diablo 
Johanna  10,000  9,99   Warrior  Diablo 
Anub'arak 4,000  6,49   Warrior  World of Warcraft 
Chen  7,000  8,49   Warrior  World of Warcraft 
Arthas  7,000  8,49   Warrior  World of Warcraft 
Diablo  7,000  8,49   Warrior  Diablo 
E.T.C.  2,000  3,99   Warrior  World of Warcraft 
Muradin  2,000  3,99   Warrior  World of Warcraft 
Sonya  4,000  6,49   Warrior  Diablo 
Stitches 7,000  8,49   Warrior  World of Warcraft 
Tyrael  4,000  6,49   Warrior  Diablo 
Cho         Warrior  World of Warcraft 
Gall         Assassin World of Warcraft 
The Butche 10,000  9,99   Assassin Diablo 
Kael'thas 10,000  9,99   Assassin World of Warcraft 
Thrall  10,000  9,99   Assassin World of Warcraft 
Jaina  4,000  6,49   Assassin World of Warcraft 
Tychus  4,000  6,49   Assassin Starcraft 
Falstad  7,000  8,49   Assassin World of Warcraft 
Illidan  4,000  6,49   Assassin World of Warcraft 

而且我想查詢一個選擇的5個不同的角色和5名隨機的名字，即這樣的：

name  role 
---------- --------- 
Sylvanas Specialis 
The Lost V Specialis 
Azmodan  Specialis 
Zagara  Specialis 
Murky  Specialis 
Johanna  Warrior 
Anub'arak Warrior 
Chen  Warrior 
Arthas  Warrior 
Stitches Warrior 
The Butche Assassin 
Kael'thas Assassin 
Thrall  Assassin 
Jaina  Assassin 
Tychus  Assassin 
Lt. Morale Support 
Kharazim Support 
Reghar  Support 
Brightwing Support 

我嘗試使用Limit但只給出了表的前5個要素。

怎麼辦？

EDIT1：

SELECT * FROM 
    (SELECT hero.name, hero.role 
    FROM hero 
    INNER JOIN 
    (SELECT DISTINCT role FROM hero 
    LIMIT 1 OFFSET 1) n 
    ORDER BY RANDOM() LIMIT 5) As t1 

UNION 

SELECT * FROM 
    (SELECT hero.name, hero.role 
    FROM hero 
    INNER JOIN 
    (SELECT DISTINCT role FROM hero 
    LIMIT 1 OFFSET 2) n 
    ORDER BY RANDOM() LIMIT 5) As t2 

UNION 

SELECT * FROM 
    (SELECT hero.name, hero.role 
    FROM hero 
    INNER JOIN 
    (SELECT DISTINCT role FROM hero 
    LIMIT 1 OFFSET 3) n 
    ORDER BY RANDOM() LIMIT 5) As t3 

UNION 

SELECT * FROM 
    (SELECT hero.name, hero.role 
    FROM hero 
    INNER JOIN 
    (SELECT DISTINCT role FROM hero 
    LIMIT 1 OFFSET 4) n 
    ORDER BY RANDOM() LIMIT 5) As t4 

UNION 

SELECT * FROM 
    (SELECT hero.name, hero.role 
    FROM hero 
    INNER JOIN 
    (SELECT DISTINCT role FROM hero 
    LIMIT 1 OFFSET 5) n 
    ORDER BY RANDOM() LIMIT 5) As t5 

這是後我改變了它與我的表@Parfait

Answer 1

考慮對每個不同的角色使用5個隨機名的聯合查詢。由於UNION查詢不支持多個LIMIT和ORDER BY子句，因此使用表別名。偏移量用於列出不同角色的列表。

SELECT * FROM 
    (SELECT g.name, g.role 
    FROM games g 
    WHERE g.role = 'Specialist' 
    ORDER BY RANDOM() LIMIT 5) As t1 

UNION 

SELECT * FROM 
    (SELECT g.name, g.role 
    FROM games g 
    WHERE g.role = 'Support' 
    ORDER BY RANDOM() LIMIT 5) As t2 

UNION 

SELECT * FROM 
    (SELECT g.name, g.role 
    FROM games g 
    WHERE g.role = 'Warrior' 
    ORDER BY RANDOM() LIMIT 5) As t3 

UNION 

SELECT * FROM 
    (SELECT g.name, g.role 
    FROM games g 
    WHERE g.role = 'Assassin' 
    ORDER BY RANDOM() LIMIT 5) As t4 

UNION 

SELECT * FROM 
    (SELECT g.name, g.role 
    FROM games g 
    WHERE g.role = 'Admin' 
    ORDER BY RANDOM() LIMIT 5) As t5; 

Answer 2

工作，如果你知道你想要的5個角色，你發送的代碼，你可以在5子查詢使用限制然後聯合在一起：

select name, role from mytable where role = 'Support' limit 5 
union all 
select name, role from mytable where role = 'Assassin' limit 5 
union all 
select name, role from mytable where role = 'Warrior' limit 5 
union all 
select name, role from mytable where role = 'Specialist' limit 5 
union all 
select name, role from mytable where role = 'Mom' limit 5 

SQL不是隨意行選擇超好，但如果你有行ID，你可以使用蘭特（）（如果你正在使用MySQL），並用它來町有一個隨機的行ID。你提到的和我使用的限制5可能會每次都返回一組非常類似的行。