mysql - 每个城市的最近一年和项目

Question

我有两张 table 。一个是市政当局 (wsjg_mun)，另一个是项目 (wsjg_proj)。我需要每个自治市最近的年份 (yr) 和项目 (proj_id)。

Table wsjg_mun (municipalities)

    pol_id (hash version of municipality name)
    mun (municipality name)
    cbs_cde
    cbs_id (municipality id, PK)

Table wsjg_proj (projects)

    cbs_id (municipality id)
    yr (year project)
    edition
    proj_id (project)
    lud

这个查询

SELECT a.pol_id, a.mun, a.cbs_cde, a.cbs_id,  yr, b.edition FROM wsjg_proj b   
LEFT JOIN wsjg_mun a 
ON a.cbs_id = b.cbs_id
GROUP BY b.cbs_id, b.yr
ORDER BY  b.cbs_id , b.yr asc

结果:

Bedum     2010  BP
Bedum     2011  BR
Bedum     2014  BP  
Ten Boer  2011  BR
Ten Boer  2013  BP

我想拥有

Bedum     2014  BP  
Ten Boer  2013  BP

Answer 1

我认为这样的查询会很有用:

SELECT a.mun, b.yr, b.edition
FROM wsjg_mun a
  LEFT JOIN wsjg_proj b ON a.cbs_id = b.cbd_id
WHERE b.yr = (
        SELECT Max(bi.yr) 
        FROM wsjg_proj bi
        WHERE bi.cbs_id = b.cbs_id)