SQL Run query across multiple Databases

I use a simple cursor to accomplish this....it's pretty straight forward and you can run any statement within it, against the list of databases.

    --Drop temporary tables if they already exists.
IF OBJECT_ID('tempdb..#DatabaseNames') IS NOT NULL
    DROP TABLE #DatabaseNames

IF OBJECT_ID('tempdb..#Results') IS NOT NULL
    DROP TABLE #Results

--Create a temporary table.
CREATE TABLE #DatabaseNames
(
    DBName varchar(100),
    Active bit
)

GO

--Create a temporary table to store results.
CREATE TABLE #Results
(
    FirstName varchar(100),
    WebLogin varchar(100)
)

GO

--It's the long way to do this but just showing for the sake of the example.
INSERT INTO #DatabaseNames
VALUES ('Database1', 1)

INSERT INTO #DatabaseNames
VALUES ('Database2', 0)

INSERT INTO #DatabaseNames
VALUES ('Database3', 1)

INSERT INTO #DatabaseNames
VALUES ('TIER1', 1)

INSERT INTO #DatabaseNames
VALUES ('Northwind', 1)

DECLARE @DBName varchar(20)
DECLARE @SQL   varchar(2000)

--Start cursor
DECLARE LoopCursor CURSOR FOR
    SELECT DBName AS 'DBName'
    FROM #DatabaseNames
    WHERE DBName NOT IN ('TIER1', 'Northwind')
    AND Active = 1

    OPEN LoopCursor

    FETCH NEXT FROM LoopCursor
    INTO @DBName

    WHILE @@FETCH_STATUS = 0
    BEGIN

        SET @SQL = '
        INSERT INTO #Results
        SELECT FirstName, WebLogin
        FROM ' + @DBName + '.dbo.Users
        WHERE FirstName = ''User1''
        AND LastName = ''User1''
        AND WebLogin = ''User1Login'''

        EXEC(@SQL)
        --Print @DBName

        FETCH NEXT FROM LoopCursor
        INTO @DBName
    END

    SELECT *
    FROM #Results

    CLOSE LoopCursor
    DEALLOCATE LoopCursor

I modified my answer again to go with your last comment about wanting all the results in one table. You can add another temporary table and just insert the data into that. Then once done, select from that table before closing the cursor. As for having many criteria in the WHERE clause, you can enclose single quotes with 2 singles quotes, so WHERE name = 'MyName' becomes WHERE name = ''MyName''

BTW, I cursors aren't the most CPU friendly and most don't like using them but they have their place. I'm not suggesting this is the best solution but it works well. We have over 75 customer databases, all having the same structure, and I use this daily to update user fields and other table fields. It runs pretty fast for executing so many statements on so many databases.