USE sets the database context that the following SQL will run under, you can't change context half way though like that.
Instead table names come in four parts,
server.database.schema.tablename
for shorthand we can leave off everything but the table name, but when querying over multiple databases we have to specify the database. In GP schema is almost always dbo, although this the default schema and default schemas can be omitted so you may sometimes see double dots with no schema given.
FLORI.dbo.PM00200 and FLORI..PM00200 are both ok.
Also your semi colon end a SQL statement so that semicolon on your FEDER needs to come out or it will end the statement early, then SQL will wonder why you are starting the next statement with UNION ALL.
USE FLORI
SELECT 'Florida' AS Co, *
FROM FLORI.dbo.PM00200
WHERE VENDSTTS = 1
UNION ALL
SELECT 'Federation' AS Co, *
FROM FEDER.dbo.PM00200
WHERE VENDSTTS = 1;
UNION ALL
SELECT 'Hudelson' AS Co, *
FROM PREPH.dbo.PM00200
WHERE VENDSTTS = 1
UNION ALL
SELECT 'Northern' AS Co, *
FROM PREPN.dbo.PM00200
WHERE VENDSTTS = 1;
I've not ran this against anything, but I guess it will be ok, assuming all your database have the same number of columns in the PM00200, something funky would be going on if they didn't, like one company is not on same version of GP as others, for example...
Have fun - SQL is addictive.
Tim.
P.S.
If you want to prioritise which company should provide the record to copy (say one company is more likely to have accurate info than another), then you can set a priority against each one then select only the first occurrence of a Vendor ID. So for fun this script will only list each vendor id once, and only the one with the highest priority donor company.
Don't be put off, go Google each bit of the SQL and you'll learn some helpful things!
USE FLORI
WITH CTE_Union AS(
SELECT 1 as [priority], 'Florida' AS Co, *
FROM FLORI.dbo.PM00200 WHERE VENDSTTS = 1
UNION ALL
SELECT 2 as [priority],'Federation' AS Co, *
FROM FEDER.dbo.PM00200 WHERE VENDSTTS = 1
UNION ALL
SELECT 3 as [priority],'Hudelson' AS Co, *
FROM PREPH.dbo.PM00200 WHERE VENDSTTS = 1
UNION ALL
SELECT 4 as [priority],'Northern' AS Co, *
FROM PREPN.dbo.PM00200 WHERE VENDSTTS = 1),
CTE_Distinct AS
(
SELECT ROW_NUMBER() OVER (PARTITION BY VENDORID ORDER BY [priority] ASC) as RowIDPriority, * FROM CTE_Union
)
SELECT * FROM CTE_Distinct WHERE RowIDPriority=1
ORDER BY VENDORID;