那时的情况,但是当时和之前有AND条件

Question

在下面的查询中,我想在CASE的WHEN中添加一个AND条件,然后才可以这样做？

例如WHEN'r'和table1.name ="jones"那么'非常高'

SELECT table1.id, table1.name,
   CASE table1.event
     WHEN 'r' THEN 'very high'
     WHEN 't' THEN 'very low'
     ELSE (SELECT table2.risk FROM table2 WHERE table2.value <= table1.value
           ORDER BY table2.value DESC LIMIT 1)
   END AS risk
FROM table1
ORDER BY FIELD( table1.event, 'r', 'f', 't' ), table1.value DESC

Answer 1

你可以像这样重写你的陈述来完成你想要的

SELECT table1.id, table1.name,
   CASE 
     WHEN table1.event = 'r' AND table1.name = 'jones' THEN 'very high'
     WHEN table1.event = 't' AND table1.name = 'smith' THEN 'very low'
     ELSE (SELECT table2.risk FROM table2 WHERE table2.value <= table1.value
           ORDER BY table2.value DESC LIMIT 1)
   END AS risk
FROM table1
ORDER BY FIELD( table1.event, 'r', 'f', 't' ), table1.value DESC

请注意,您需要table1.event在CASE声明后删除. 文档在这里

Answer 2

任何评估为布尔值(true或false)的东西都可以在语句的WHEN条件下CASE.所以你可以替换'r'为:

('r' AND table1.name='jones')

考虑到这一点,你可能不得不失去table1.event后CASE

SELECT table1.id, table1.name,
    CASE 
        WHEN (table1.event = 'r' AND table1.name='Jones') THEN 'very high'
        WHEN table1.event = 't' THEN 'very low'
        ELSE (SELECT table2.risk 
              FROM table2 
              WHERE table2.value <= table1.value 
              ORDER BY table2.value DESC LIMIT 1)
    END AS risk
FROM table1
ORDER BY FIELD( table1.event, 'r', 'f', 't' ), table1.value DESC