SQL Oracle 10g：列为空，但不为空或空字符串
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Oracle 10g: column is blank, but is not null or an empty string
提问by Josh
I have a column in a table that is blank. The weird thing is that it does not appear to be null or an empty string. So, if I do this:
我在一个空白的表格中有一个列。奇怪的是，它似乎不是 null 或空字符串。所以，如果我这样做：
SELECT *
FROM TABLE
WHERE column IS NULL
...or:
...或者：
SELECT *
FROM TABLE
WHERE column = ''
I get nothing. Thoughts?
我什么也得不到。想法？
回答by álvaro González
Issue this query:
发出此查询：
SELECT column, DUMP(column, 1016)
FROM table
It'll show the exact contents.
它将显示确切的内容。
Related: Oracle does not allow empty strings; they're silently converted to NULL.
相关：Oracle 不允许空字符串；他们默默地转换为NULL.
回答by a_horse_with_no_name
Maybe the column contains only spaces?
也许该列只包含空格？
Did you try
你试过了吗
select * from table where trim(column) is null
回答by Marc B
Oracle's got a basically permanent annoyance that empty strings are treated as null. However, are you sure that's an empty string? It could be an otherwise invisible character, such as a space or tab/linebreak/linefeed/etc... What does the string length show when you do select length(column) from table?
Oracle 有一个基本永久的烦恼，即空字符串被视为空字符串。但是，您确定这是一个空字符串吗？它可能是一个不可见的字符，例如空格或制表符/换行符/换行符/等......当你这样做时，字符串长度显示什么select length(column) from table？
回答by Chandu
Try this:
尝试这个：
SELECT *
FROM TABLE
WHERE TRIM(column) IS NULL
回答by Benoit
If your column is not VARCHAR2but CHAR(N)then insertion of an empty string is padded. See what Tom Kyte tells about this
如果您的列不是VARCHAR2，CHAR(N)则填充空字符串的插入。看看Tom Kyte 是怎么说的
