select impala 的 case 语句中的语句

Question

我需要消除案例中的硬编码值，并开发了一个查找 table 来获取这些值。

查找 table 看起来像：

serial_no   code    description type

1       J   Jol           CENTRE_TYPE
3       C   Cols          CENTRE_TYPE
4       R   Rud           CENTRE_TYPE
2       A   TCD           CENTRE_TYPE

我有以下 impala 代码：

SELECT `prtc`,
    CASE   WHEN LEFT(prtc,1) = 'C' THEN  (SELECT DESCRIPTION FROM dev.lookup_table WHERE CODE='C' AND TYPE='CENTRE_TYPE')
            WHEN LEFT(prtc,1) = 'A' THEN (SELECT DESCRIPTION FROM dev.lookup_table WHERE CODE='A' AND TYPE='CENTRE_TYPE')
            WHEN LEFT(prtc,1) = 'R' THEN (SELECT DESCRIPTION FROM dev.lookup_table WHERE CODE='R' AND TYPE='CENTRE_TYPE')
            WHEN LEFT(prtc,1) = 'J' THEN (SELECT DESCRIPTION FROM dev.lookup_table WHERE CODE='J' AND TYPE='CENTRE_TYPE')
    END AS CENTRE_TYPE
FROM dev.`tablename`

我收到一个错误 "AnalysisException: Could not resolve table reference: 'dev.lookup_table'"

Answer 1

使用连接：

SELECT t.prtc,
       l.DESCRIPTION  as CENTRE_TYPE
FROM dev.`tablename` t
     left outer join dev.lookup_table l on LEFT(t.prtc,1)= l.CODE and l.TYPE='CENTRE_TYPE'

select impala 的 case 语句中的语句

select statement inside case statement for impala

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impala