Mysql计数选定查询

Question

请看下表。可以说第一个是table1和table2另一个。 我真的不知道该怎么做，任何人都可以帮助我如何计算像下面的表与MySQL查询？

它算你“一”

感谢

Answer 1

多少“红色”与类型需要使用LEFT JOIN而INNER JOIN因为有一种可能性，即color不会对其他存在表。

SELECT a.id, 
     a.colour, 
     SUM(type = 'a') TypeA, 
     SUM(type = 'b') TypeB 
FROM tableColors a 
     LEFT JOIN tableName b 
      ON a.ncolour = b.colour 
GROUP BY a.id, a.colour 

SUM(type = 'a')是计算来自布尔运算的结果的合计值一个MySQL特定语法。如果你想更RDBMS友好，使用CASE

SELECT a.id, 
     a.colour, 
     SUM(CASE WHEN type = 'a' THEN 1 ELSE 0 END) TypeA, 
     SUM(CASE WHEN type = 'b' THEN 1 ELSE 0 END) TypeB 
FROM tableColors a 
     LEFT JOIN tableName b 
      ON a.ncolour = b.colour 
GROUP BY a.id, a.colour 

Answer 2

你可以做这样的事情，从表1 SELECT COUNT（红色）;我不知道有关语法，你可以检查在这里

http://dev.mysql.com/doc/refman/5.0/es/counting-rows.html

http://www.mysqlperformanceblog.com/2007/04/10/count-vs-countcol/

Answer 3

SELECT a.colour ncolor, 
    SUM(a.type = 'a') amount_a, 
    SUM(a.type = 'b') amount_b 
    FROM table_name a 
    LEFT JOIN table_name b 
    ON a.colour = b.colour 
    GROUP BY a.id, a.colour 

Answer 4

从你的屏幕，我说你要找的查询是一个简单的SELECT [...], COUNT(a), COUNT(b) FROM table1 GROUP BY colour 。

更确切地说：

SELECT colour AS ncolour 
    , COUNT(a) as amount_a 
    , COUNT(b) as amount_b 
FROM table1 
GROUP BY colour ; 

见Mysql Counting Rows

附：我认为所要求的是MySQL查询从table1获取table2。