mysql - 如何解决 left join with where 子句不起作用

Question

我有一个使用 LEFT JOIN 和 WHERE 子句的查询，但是当我运行查询时，不匹配的数据不会显示在数据库中。我该如何解决这个问题？

SELECT tbguru.id, tbabsenpeg.NIK, tbabsenpeg.tgl 
FROM `tbguru` 
LEFT JOIN tbabsenpeg ON tbguru.id = tbabsenpeg.NIK AND tbguru.kodeapp = tbabsenpeg.kodeapp 
WHERE tbguru.kodeapp='Mantri-Lab 1020' 
AND (tbabsenpeg.tgl = '2019-03-09' OR tbabsenpeg.tgl IS NULL);

Answer 1

我认为您需要 on 子句中第二张表的条件:

SELECT g.id, a.NIK, a.tgl 
FROM tbguru g LEFT JOIN
     tbabsenpeg a
     ON g.id = a.NIK AND
        g.kodeapp = a.kodeapp AND
        a.tgl = '2019-03-09'
WHERE g.kodeapp = 'Mantri-Lab 1020' ;