JAVA条件逻辑到Impala查询答案

【问题标题】：JAVA conditional logic to Impala queryJAVA条件逻辑到Impala查询
【发布时间】：2021-01-20 12:34:28
【问题描述】：

我在 JAVA 中有一个处理数据库的条件逻辑，我想将其转换为 Impala。我对在 impala 中使用“CASE WHEN”和“IF”函数感到困惑，那么下面哪个 impala 逻辑更好用？对吗？

逻辑上发生的事情是，如果主要条件为真，我正在尝试从第一个表 (table_seller_inside) 中获取列 (seller_id)。然后检查 seller_id 是否为 null，然后我会从另一个表中获取 (table_seller_outside)

JAVA逻辑：

if(temp_table.col_1!=null && !temp_table.col_2.trim().equals("") )
{
-> table_seller_inside.seller_id

    if(seller_id==null) 
    {
    -> table_seller_outside.seller_id
    }
}

Impala 逻辑与 CASE WHEN：

SELECT CASE WHEN temp_table.col_1 IS NOT NULL THEN 
            sel_in.seller_id as seller_id,
            sel_in.seller_name as seller_name,
            sel_in.seller_number as seller_num
            CASE WHEN (seller_id IS NULL) THEN
                sel_out.seller_id as seller_id,
                sel_out.seller_name as seller_name,
                sel_out.seller_number as seller_num,
            END
       END
FROM table_seller_inside sel_in,
     table_seller_outside sel_out

IF 的 Impala 逻辑：

if(boolean condition, type ifTrue, type ifFalseOrNull)

SELECT if(temp_table.col_1 !="NULL", (sel_in.seller_id as seller_id,
                                     sel_in.seller_name as seller_name,
                                     sel_in.seller_number as seller_num),
            if(seller_id ="NULL", (sel_out.seller_id as seller_id,
                                   sel_out.seller_name as seller_name,
                                   sel_out.seller_number as seller_num)
FROM table_seller_inside sel_in,
     table_seller_outside sel_out

【问题讨论】：

标签： if-statement case impala

【解决方案1】：

你可以使用下面的sql。您需要提及所有关联表之间的连接或关系。个别情况何时会在这里工作。 JAVA代码使用if-else，所以可以使用wither case when或if()。

SELECT CASE
           WHEN temp_table.col_1 IS NOT NULL
                AND TRIM(temp_table.col_2)<>'' THEN sel_in.seller_id
           ELSE sel_out.seller_id
       END AS seller_id,
       CASE
           WHEN temp_table.col_1 IS NOT NULL
                AND TRIM(temp_table.col_2)<>'' THEN sel_in.seller_name
           ELSE sel_out.seller_name
       END AS seller_name ,
       CASE
           WHEN temp_table.col_1 IS NOT NULL
                AND TRIM(temp_table.col_2)<>'' THEN sel_in.seller_number
           ELSE sel_out.seller_number
       END AS seller_number
FROM table_seller_inside sel_in,
     table_seller_outside sel_out,
     temp_table
WHERE -- you need to give join condition/relations
sel_in.id = sel_out.id
  AND temp_table.key = sel_out.key

【讨论】：

感谢您的帮助。但我实际上拥有的是查看seller_id，并尝试从第一个表中批量获取（seller_id，seller_name，seller_number），然后如果第一个表中不存在“seller_id”，所以我会采取第二个表中的批量（seller_id、seller_name、seller_number）。并且连接已经在原始查询中指定。