SQL 服务器：无法插入默认列值

Question

I've created a table like this

CREATE TABLE dbo.[Users] 
(
    [UserID_PK] INT IDENTITY(1, 1) PRIMARY KEY NOT NULL,
    [Email] NVARCHAR(60) NOT NULL,
    [Username] NVARCHAR(15) NOT NULL,
    [Password] NVARCHAR(24) NOT NULL,
    [Salt] NVARCHAR(24) NOT NULL,
    [Token] NVARCHAR(200),
    [DateCreated] DATETIME DEFAULT (GETDATE()) NOT NULL
);

Every time my API creates a record, it returns this message. I am not sure why the default value isn't being inserted instead of NULL. I've tried GETDATE() and CURRENT_TIMESTAMP :

Cannot insert the value NULL into column 'DateCreated'; column does not allow nulls. INSERT fails.

Answer 1

The root cause: The problem is not with how you defined default for the DateCreated column on the table it's with your insert statement.

How to implicitly use default value: If you want the default value to be used make sure to not include the column(s) defined with default in the insert statement your using. Example: insert into dbo.Users(Name) select 'someName' Your column(s) defined with default will get the default value implicitly if you don't explicitly include it as a column in the insert statement when inserting row(s).

Why you are getting the error: You are getting this Error:

Cannot insert the value NULL into column 'DateCreated'; column does not allow nulls. INSERT fails.

because you're explicitly including the DateCreated column in your insert statement and not providing a value, something like: insert into dbo.Users(Email,DateCreated) select 'someName'

Resolution: To resolve this provide a value for the column like this: insert into dbo.Users(Email,DateCreated) select 'someEmail',getdate() or remove DateCreated from the insert and it will implicitly get the default value even if you don't include it as a column when you insert values for other columns on the row. You can even hard code a string literal date value '2020-08-22 19:05:00' to set a specific date time if you don't want to use getdate() or another similar date function.

Answer 2

In SQL Server, you have two options for inserting a default value. One is to leave out the column:

insert into users (email, username, password, salt, token)
    values (?, ?, ?, ?, ?);

The second is to use the default keyword:

insert into users (email, username, password, salt, token, dateCreated)
    values (?, ?, ?, ?, ?, default);

NULL is not a synonym for DEFAULT .

I should point out that there is actually a third way. That requires navigating the metadata.tables to look up the default value for a column. As a general rule, that approach is not useful. On occasion, it can be quite helpful.