我试图在不丢失内容的情况下将 varchar 列的长度从 255 个字符更新为 500 个字符.我之前删除并重新创建了表,但我从未接触过 alter 语句,我相信我需要使用它来执行此操作.我在这里找到了文档:ALTER TABLE (Transfact-SQL) 但是我不能让它正面或反面.
I'm trying to update the length of a varchar column from 255 characters to 500 without losing the contents. I've dropped and re-created tables before but I've never been exposed to the alter statement which is what I believe I need to use to do this. I found the documentation here: ALTER TABLE (Transfact-SQL) however I can't make heads or tails of it.
到目前为止,我有以下内容(不幸的是,基本上没有):
I have the following so far (essentially nothing unfortunately):
alter table [progennet_dev].PROGEN.LE
alter column UR_VALUE_3
我该如何解决这个问题?是否有关于此语句的更好的文档(我搜索了一些示例语句,但结果为空)?
How do I approach this? Is there better documentation for this statement out there (I did some searches for an example statement but came up empty)?
您需要
ALTER TABLE YourTable ALTER COLUMN YourColumn <<new_datatype>> [NULL | NOT NULL]
但请记住,如果需要,请明确指定 NOT NULL
.
But remember to specify NOT NULL
explicitly if desired.
ALTER TABLE YourTable ALTER COLUMN YourColumn VARCHAR (500) NOT NULL;
如果你不指定如下...
If you leave it unspecified as below...
ALTER TABLE YourTable ALTER COLUMN YourColumn VARCHAR (500);
然后该列将默认允许空值,即使它最初定义为 NOT NULL
.即省略 ALTER TABLE ... ALTER COLUMN
中的规范总是被视为.
Then the column will default to allowing nulls even if it was originally defined as NOT NULL
. i.e. omitting the specification in an ALTER TABLE ... ALTER COLUMN
is always treated as.
ALTER TABLE YourTable ALTER COLUMN YourColumn VARCHAR (500) NULL;
此行为不同于用于使用 ALTER TABLE
(或在 CREATE TABLE
时间)创建的新列的行为.默认的可空性取决于 ANSI_NULL_DFLT
设置.
This behaviour is different from that used for new columns created with ALTER TABLE
(or at CREATE TABLE
time). There the default nullability depends on the ANSI_NULL_DFLT
settings.
这篇关于更改 varchar 列的最大长度?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持html5模板网!