SQL 根據另一個 Columns 值更新 Select Statement 列，但前提是滿足條件

Question

如果列task_status2的值為Closed ，我有一個 select 語句，並希望將Task_Days_Due更新為字符串（ N/A - Task is Closed ）當前它顯示到期前的天數，但如果關閉則無關緊要。

這是當前的選擇：

SELECT

    Report_Run_Date,
    incident_number,
    INC_Reported_Date,
    TASK_id,
    TASK_Assigneee, 
    TASK_Status, -- Staged 1000, Assigned 2000, Pending 3000, Work In Progress 4000, Waiting 5000, Closed 6000, ByPassed 7000
    Task_Status2,
    -- Set RAG column to RAG is not closed
    case    WHEN TASK_Status = 6000  THEN "N/A - Task is Closed"
            WHEN Task_Days_Due <= 0  THEN 'Red'
            WHEN Task_Days_Due > 0 and Task_Days_Due <= 7 THEN 'Amber'
            WHEN Task_Days_Due > 7 THEN 'Green'
            WHEN Task_Days_Due is NULL THEN 'No Task End Date'
    end     as Red_Amber_Green,
    Task_Days_Due, ?????

我的挑戰是如果不滿足條件，我想保持原樣。 如果列task_status2值未Closed ，則先前的嘗試將值覆蓋為 null

Answer 1

SELECT

    Report_Run_Date,
    incident_number,
    INC_Reported_Date,
    TASK_id,
    TASK_Assigneee, 
    TASK_Status, -- Staged 1000, Assigned 2000, Pending 3000, Work In Progress 4000, Waiting 5000, Closed 6000, ByPassed 7000
    Task_Status2,
    -- Set RAG column to RAG is not closed
    case    WHEN TASK_Status = 6000  THEN "N/A - Task is Closed"
            WHEN Task_Days_Due <= 0  THEN 'Red'
            WHEN Task_Days_Due > 0 and Task_Days_Due <= 7 THEN 'Amber'
            WHEN Task_Days_Due > 7 THEN 'Green'
            WHEN Task_Days_Due is NULL THEN 'No Task End Date'
    end     as Red_Amber_Green,
    decode(task_status2, 'Closed', 'N/A - Task is Closed', cast(task_days_due as STRING)) as task_days_due