How to detect a SQL Server database's read-only status using T-SQL?

The information is stored in sys.databases.

SELECT name, is_read_only 
FROM sys.databases 
WHERE name = 'MyDBNAme'
GO

--returns 1 in is_read_only when database is set to read-only mode.

Querying sys.databases for checking a DB's Read-Only property will only give the right information if the database has been explicitly set to Read-Only mode.

For databases that are in the passive servers (e.g. in AlwaysOn technology Secondary Servers), even though the databases cannot be written into, their Read-Only mode in sys.databases would still be set as False(0).

Hence, it is advisable to check the Read-Only mode of databases using the statement:

SELECT DATABASEPROPERTYEX('MyDBNAme', 'Updateability');

Here is a command to display or set this property.

EXEC sp_dboption "AdventureWorks", "read only"

Sample output

OptionName CurrentSetting    
read only OFF