MySQL的 - 選擇列，只有當他們具有值

我需要幀MySQL查詢，其中有接列的要求，僅當它具有值（爲NOT NULL）從4列的給定的，first_accuracy，second_accuracy ，third_accuracy，fourth_accuracy。MySQL的 - 選擇列，只有當他們具有值

假設我有隻爲first_accuracy，second_accuracy值，所以查詢應該是

SELECT first_accuracy，second_accuracy FROM compliance_employees CE;

UPDATE：

查詢我申請：

SELECT first_accuracy, second_accuracy, third_accuracy, fourth_accuracy FROM compliance_employees CE;

結果：

您可以看到，對於「第三精度」，沒有任何行的值，所以我根本不想選擇該列。那可能嗎？

任何解決方案？

來源

2017-01-06 Rajesh Omanakuttan

我想'山坳不null'？ – GurV

... WHERE CE.first_accuracy不爲NULL且CE.second_accuracy不爲NULL且CE.third_accuracy IS NULL和CE.fourth_accuracy IS NULL＃ – spencer7593

如果不使用動態SQL，則無法執行此操作。但你爲什麼要這樣做？只需使用'COALESCE（）'來處理每列中的NULL值。 –

如果你只是想確保兩列first_accuracy和second_accuracy不NULL然後使用此：

SELECT first_accuracy, 
     second_accuracy 
FROM compliance_employees CE 
WHERE first_accuracy IS NOT NULL AND 
     second_accuracy IS NOT NULL

如果你想確保所有四列不NULL然後使用這個：

SELECT first_accuracy, 
     second_accuracy 
FROM compliance_employees CE 
WHERE first_accuracy IS NOT NULL AND 
     second_accuracy IS NOT NULL AND 
     third_accuracy IS NOT NULL AND 
     fourth_accuracy IS NOT NULL

來源

2017-01-06 04:32:31

我想我沒有把我的問題框架得很好，它不僅僅是'NOT NULL'..不過感謝你的幫助.. –

@RajeshOmanakuttan這回答你的問題，因爲你有它的措辭。如果你的意思是別的，那麼更新並向我們展示樣本數據。 –

當然，我正在做它.. –

SELECT 
    first_accuracy, 
    second_accuracy 
FROM 
    compliance_employees CE 
WHERE 
    first_accuracy IS NOT NULL 
    AND second_accuracy IS NOT NULL

來源

2017-01-06 04:34:40 JustSomeDude

您的意思是問如何選擇在v四個領域中的一個？如果是的話，我建議使用GREATEST：

SELECT 
    GREATEST(first_accuracy, second_accuracy) as accuracy 
FROM 
    compliance_employees CE;

來源

2017-01-06 04:46:38

使用「聯盟」，GROUP_CONCAT（）和「不爲空」，我們發現其中有值列數。然後傳遞列給準備好的陳述，它給你你想要的結果。

 select coalesce (GROUP_CONCAT(col_name),'No_Result') into @ColumnNames 
     from (
     select 'first_accuracy' as col_name, count(distinct first_accuracy) as count from compliance_employees 
     where first_accuracy is not null 
     union 
     select 'second_accuracy' as col_name, count(distinct second_accuracy) from compliance_employees 
     where second_accuracy is not null 
     union 
     select 'third_accuracy' as col_name, count(distinct third_accuracy) from compliance_employees 
     where third_accuracy is not null 
     union 
     select 'fourth_accuracy' as col_name, count(distinct fourth_accuracy) from compliance_employees 
     where fourth_accuracy is not null 
     )a where count >0\\ 
     -- select @ColumnNames\\ 


    SET @sql := CONCAT('SELECT ', @ColumnNames, ' FROM compliance_employees'); 
    set @sql := REPLACE(@sql,'No_Result','"No Column have values" as No_Result')\\ 

    PREPARE stmt FROM @sql; 
    EXECUTE stmt;

檢查現場演示Here。

輸出：

來源

2017-01-06 07:55:47

如果所有字段都爲空，則查詢會引發錯誤。否則，這是一個很好的答案。 –

@PrabirGhosh third_accuracy COLUMN有所有字段空值..你想說什麼？ –

只要嘗試所有列的所有字段的罕見情況爲空。但根據我的觀點，你的答案是最好的。 –

MySQL的 - 選擇列，只有當他們具有值

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