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Question

I have a table with full text index created on it.

CREATE TABLE dbo._mytable
(
    ID INT CONSTRAINT Pk_mytable PRIMARY KEY CLUSTERED,
    Name NVARCHAR(50)
)
GO

CREATE FULLTEXT CATALOG ft AS DEFAULT
GO  

CREATE FULLTEXT INDEX ON dbo._mytable(Name)   
   KEY INDEX Pk_mytable   
GO

The following query runs successfully

SELECT t.Name AS t_name
FROM dbo._mytable t
WHERE CONTAINS(t.Name, '"mu*"')

But this one fails

SELECT *
FROM 
    (SELECT t.Name AS t_name
     FROM dbo._mytable t) T
WHERE CONTAINS(T.t_name, '"mu*"')

Error:

Msg 7601, Level 16, State 3, Line 7
Cannot use a CONTAINS or FREETEXT predicate on column 't_name' because it is not full-text indexed

Answer 1

The second one trows an error, because you are not selecting from the table with the full text index, but from a derived table . The engine can't move the full text search from the outer select to the inner one.