Oracle varchar2 最小长度
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Oracle varchar2 minimum length
提问by vrm
In Oracle db we have a table with varchar2 type of column (for example USERNAME). How can I set a exact (or at least minimum) length for this column? So that all usernames inserted into this table can be only 10 (or have to be at least 10) characters long.
在 Oracle db 中，我们有一个带有 varchar2 类型列的表（例如 USERNAME）。如何为此列设置精确（或至少是最小）长度？因此，插入该表的所有用户名只能是 10 个（或必须至少为 10 个）字符长。
回答by skaffman
You could use a check constraint:
您可以使用检查约束：
CREATE TABLE mytable (
mycolumn varchar2(50),
constraint strlen check (length(mycolumn) > 2)
)
Or something similar. I'm not sure how performant this is, though.
或者类似的东西。不过，我不确定它的性能如何。
回答by William Robertson
Or just for fun,
或者只是为了好玩，
CREATE TABLE testit
( mycolumn VARCHAR2(20) CONSTRAINT min_length_chk CHECK (mycolumn LIKE '__%') );
It's less explicit than the LENGTH() approach though so I'm not sure I'm recommending it except as an idea for related issues.
虽然它不如 LENGTH() 方法明确，所以我不确定我是否推荐它，除非作为相关问题的想法。
