Question

我在下面遇到了一个问题

SELECT ColumnName1,* 
FROM TableName 
WHERE ColumnName = 'XXXXXX'
ORDER BY ColumnName1

从上面的查询中，它以歧义的列名Column Name1引发错误。

即使我没有使用过数字表，它也会引发这样的错误。谁能说出这背后的原因吗？

Answer 1

因为SELECT有两列称为ColumnName1 －一列明确放置在其中，而另一列则来自*。这里有一些选择：

SELECT t.ColumnName1, t.*
FROM TableName t
WHERE t.ColumnName = 'XXXXXX'
ORDER BY t.ColumnName1

或：

SELECT t.ColumnName1, t.*
FROM TableName t
WHERE t.ColumnName = 'XXXXXX'
ORDER BY 1

或：

SELECT t.ColumnName1 as second_columnname1, t.*
FROM TableName t
WHERE t.ColumnName = 'XXXXXX'
ORDER BY second_columnname1

Answer 2

要解决错误，我们提供3个选项：

-- 1. give alias to the column
SELECT A AS A_STANDS_ALONE, * 
FROM YourTable
ORDER BY A

-- 2. order by 1
SELECT A, * 
FROM YourTable
ORDER BY 1

-- 3. give alias to the table and used it in column call and order by
SELECT t.A, * 
FROM YourTable t
ORDER BY t.A

列名按子句顺序使用时出现歧义错误

2 个答案: