问题
How can I find the name of a named not-null constraint in SQL Server? I can find check constraints, default constraints, FK constraints, PK constraints and unique constraints, but the NN constraint has eluded me.
回答1:
You can't.
Whilst the syntax does accept a name...
CREATE TABLE T
(
C INT CONSTRAINT NN NOT NULL
)
... and it is parsed and validated as a name ...
CREATE TABLE T
(
C INT CONSTRAINT NN123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789 NOT NULL
)
/* The identifier that starts with 'NN1234...6' is too long. Maximum length is 128. */
... this is then ignored and isn't actually stored anywhere.
No row is added to sys.objects for these unlike other constraints. It is just stored as a bit property of the associated column rather than a constraint object.
回答2:
List columns with not-null constraint
DECLARE @Table NVARCHAR(MAX) = 'Your table name here'
SELECT
[COLUMN_NAME] AS [Column]
--, [DATA_TYPE] AS [Type]
FROM
[INFORMATION_SCHEMA].[COLUMNS]
WHERE
[IS_NULLABLE] = 'NO'
AND (@Table = '' OR [TABLE_NAME] = @Table)
ORDER BY
[TABLE_NAME]
Notes
Replace Your table name here on line 1 at the top of the query, with the name of the table you need a list for.
If you also need to know the data type of each column, uncomment line 4 by deleting the two dashes at the start of the line.
回答3:
You are able to query from the information _schema all columns that are nullable. Does that get you what you want?
SELECT
table_catalog, table_schema, table_name, column_name, is_nullable
FROM information_schema.columns
WHERE table_name = 'users'
来源：https://stackoverflow.com/questions/34096290/how-to-find-the-name-of-not-null-constraints-in-sql-server