我编辑阿贡Sagita的答案从子查询加入。 我不确定这两种方式有多大区别，但只是作为另一个参考。

SELECT  hostid, T2.VALUE AS A, T3.VALUE AS B, T4.VALUE AS C
FROM TableTest AS T1
LEFT JOIN TableTest T2 ON T2.hostid=T1.hostid AND T2.ITEMNAME='A'
LEFT JOIN TableTest T3 ON T3.hostid=T1.hostid AND T3.ITEMNAME='B'
LEFT JOIN TableTest T4 ON T4.hostid=T1.hostid AND T4.ITEMNAME='C'

我很抱歉这么说，也许我没有完全解决你的问题，但PostgreSQL比MySQL早10年，与MySQL相比是非常先进的，有很多方法可以轻松实现这一点。安装PostgreSQL并执行此查询

CREATE EXTENSION tablefunc;

然后瞧!这里有大量的文档:PostgreSQL: documentation: 9.1: tablefunc或this查询

CREATE EXTENSION hstore;

然后，瞧!PostgreSQL: Documentation: 9.0: hstore

使用子查询

SELECT  hostid, 
    (SELECT VALUE FROM TableTest WHERE ITEMNAME='A' AND hostid = t1.hostid) AS A,
    (SELECT VALUE FROM TableTest WHERE ITEMNAME='B' AND hostid = t1.hostid) AS B,
    (SELECT VALUE FROM TableTest WHERE ITEMNAME='C' AND hostid = t1.hostid) AS C
FROM TableTest AS T1
GROUP BY hostid

但如果子查询结果超过一行，则会出现问题，在子查询中使用进一步的聚合函数

我把它变成Group By hostId，然后它只会显示第一行的值， 如:

A   B  C
1  10
2      3

你可以使用几个LEFT join。请使用此代码

SELECT t.hostid,
       COALESCE(t1.itemvalue, 0) A,
       COALESCE(t2.itemvalue, 0) B,
       COALESCE(t3.itemvalue, 0) C 
FROM history t 
LEFT JOIN history t1 
    ON t1.hostid = t.hostid 
    AND t1.itemname = 'A' 
LEFT JOIN history t2 
    ON t2.hostid = t.hostid 
    AND t2.itemname = 'B' 
LEFT JOIN history t3 
    ON t3.hostid = t.hostid 
    AND t3.itemname = 'C' 
GROUP BY t.hostid

SELECT 
    hostid, 
    sum( if( itemname = 'A', itemvalue, 0 ) ) AS A,  
    sum( if( itemname = 'B', itemvalue, 0 ) ) AS B, 
    sum( if( itemname = 'C', itemvalue, 0 ) ) AS C 
FROM 
    bob 
GROUP BY 
    hostid;