问题
Can I create a database constraint on a TEXT column in SQLite disallowing the value of the column to be empty string ""?
I want to allow the column to be null, but disallow empty string.
回答1:
Yes you can:
sqlite> create table foo (bar TEXT, CHECK(bar <> ''));
sqlite> insert into foo values (NULL);
sqlite> insert into foo values ('bla');
sqlite> insert into foo values ('');
Error: constraint failed
回答2:
You can use a CHECK constraint (http://www.sqlite.org/lang_createtable.html):
SQLite version 3.5.9
Enter ".help" for instructions
sqlite> create table example(col, CHECK (col is null or length(col) > 0));
sqlite> insert into example values ('');
SQL error: constraint failed
sqlite> insert into example values (null);
sqlite> insert into example values ('sample');
sqlite> .nullvalue NULL
sqlite> select col from example;
NULL
sample
回答3:
As far as i know doesn't exist a similar constraint in SQLite, but maybe you can workaround with a Trigger that on INSERT and/or UPDATE automatically change the string empty in NULL.
来源：https://stackoverflow.com/questions/10371077/not-empty-string-contraint-in-sqlite