In Stored Procedure, how to check if variable is NULL?

[neilc]

I am assigned to convert a bunch of MSSQL stored procedure to MySQL stored procedures in version 5.0. There are syntax differences and I am stuck in many of these and the usual "syntax error" messages are not very helpful.

So I have in MSSQL:

/*GetUser*/
CREATE PROCEDURE GetUser
(
Username VARCHAR(50)
)
BEGIN
DECLARE UserID int;

SELECT UserID = UserID FROM Memberships WHERE Username = Username;
IF UserID <> NULL
SELECT FirstName, LastName, EMail FROM Users WHERE UserID = UserID;
END

In MYSQL I have so far:

/*GetUser*/
CREATE PROCEDURE `eiffelsupport`.`GetUser`
(
a_Username VARCHAR(50)
)
BEGIN
DECLARE l_UserID INT;

SELECT l_UserID = UserID FROM Memberships WHERE Username = a_Username;
IF l_UserID IS NULL
SELECT FirstName, LastName, EMail FROM Users WHERE UserID = l_UserID;
END

The problem is in how to acheive the same as IF UserID <> NULL in MYSQL?

Thanks in advance?

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NC