PWDCOMPARE (Transact-SQL)
Applies to: 
SQL Server
Azure SQL Database
Azure SQL Managed Instance
Hashes a password and compares the hash to the hash of an existing password. PWDCOMPARE can be used to search for blank SQL Server login passwords or common weak passwords.
Transact-SQL syntax conventions
Syntax
PWDCOMPARE ( 'clear_text_password'
, password_hash
[ , version ] )
Arguments
' clear_text_password '
Is the unencrypted password. clear_text_password is sysname (nvarchar(128)).
password_hash
Is the encryption hash of a password. password_hash is varbinary(128).
version
Obsolete parameter that can be set to 1 if password_hash represents a value from a login earlier than SQL Server 2000 (8.x) that was migrated to SQL Server 2005 (9.x) or later but never converted to the SQL Server 2000 (8.x) system. version is int.
Caution
This parameter is provided for backwards compatibility, but is ignored because password hash blobs now contain their own version descriptions. This feature will be removed in a future version of SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature.
Return Types
int
Returns 1 if the hash of the clear_text_password matches the password_hash parameter, and 0 if it does not.
Remarks
The PWDCOMPARE function is not a threat against the strength of password hashes because the same test could be performed by trying to log in using the password provided as the first parameter.
PWDCOMPARE cannot be used with the passwords of contained database users. There is no contained database equivalent.
Permissions
PWDENCRYPT is available to public.
CONTROL SERVER permission is required to examine the password_hash column of sys.sql_logins.
Examples
A. Identifying logins that have no passwords
The following example identifies SQL Server logins that have no passwords.
SELECT name FROM sys.sql_logins
WHERE PWDCOMPARE('', password_hash) = 1 ;
B. Searching for common passwords
To search for common passwords that you want to identify and change, specify the password as the first parameter. For example, execute the following statement to search for a password specified as password.
SELECT name FROM sys.sql_logins
WHERE PWDCOMPARE('password', password_hash) = 1 ;