How can I use the EXISTS operator? - sql-server

Question

Someone maybe can help me to use EXISTS operator to check - ev.tfe_evento = 'Inizio lettura file' and ev.tfe_evento = 'lettura file'. I need to display all files that contain inizio lettura file and lettura file. The template of code is:
SELECT column-names
FROM table-name
WHERE EXISTS (
SELECT column-name
FROM table-name
WHERE condition
)
But how I can change my code below to follow this example?
DROP TABLE IF EXISTS #tflussi_eventi;
SELECT ev.*
INTO tab1
FROM tab1 ev (nolock)
JOIN (
SELECT lab
FROM #lab1
GROUP BY labname
) tf ON ev.labnameLIKE tf.labname+ '%'
WHERE ev.labevent= 'today'
AND ev.labevent= 'yesterday'

Answer 1

Sometimes I like to use window functions when checking conditions like this. Where you are looking for multiple conditions across the group.
This is not your actual query, just to give you an idea.
With window functions:
SELECT DISTINCT fileName
FROM (SELECT E.*,
CASE WHEN MAX(CASE WHEN E.tfe_evento = 'lettura file' THEN 1
ELSE 0
END
) OVER ( PARTITION BY E.FileName ) = 1
AND MAX(CASE WHEN E.tfe_evento = 'Inizio lettura file' THEN 1
ELSE 0
END
) OVER ( PARTITION BY E.FileName ) = 1
THEN 1
ELSE 0
END AS FileHasBothEventConds
FROM EVENT E
)
WHERE FileHasBothEventConds = 1;
With EXISTS:
SELECT DISTINCT fileName
FROM EVENTS E
WHERE EXISTS
( SELECT 1
FROM EVENTS E_LF
WHERE E.fileName = E_LF.fileName
AND E_FL.tfe_evento = 'lettura file'
)
AND EXISTS
( SELECT 1
FROM EVENTS E_ILF
WHERE E.fileName = E_ILF.fileName
AND E_ILF.tfe_evento = 'Inizio lettura file'
)

Answer 2

You should use LIKE operator instead of = for that to happen. ie:
SELECT ev.*
INTO #tflussi_eventi
FROM tflussi_eventi ev (nolock)
JOIN (
SELECT FileNameCutoff
FROM #FileCutoffTime
GROUP BY FileNameCutoff
) tf ON ev.tfe_sorgente LIKE tf.FileNameCutoff + '%'
WHERE ev.tfe_evento LIKE '%Inizio lettura file%'
-- Unnecessary because of first criteria
-- AND ev.tfe_evento = 'lettura file'
AND ev.tfe_data >= #DateToCheck
AND ev.tfe_data < #DateToCheck + 1 -- not sure what you mean here, if it is datetime, using DateAdd() is safer
However, this might suffer from performance, you should think of creating fulltext indexes and use full text search.
EDIT: While it would still suffer because you are not doing a full text search, you might save, maybe negligible time on the joined table which practically has no importance other than "existence check":
SELECT ev.*
INTO #tflussi_eventi
FROM tflussi_eventi ev (nolock)
WHERE ev.tfe_evento LIKE '%Inizio lettura file%'
-- Unnecessary because of first criteria
-- AND ev.tfe_evento = 'lettura file'
AND ev.tfe_data >= #DateToCheck
AND ev.tfe_data < #DateToCheck + 1 -- not sure what you mean here, if it is datetime, using DateAdd() is safer
and EXISTS (
SELECT *
FROM #FileCutoffTime tf
where ev.tfe_sorgente LIKE tf.FileNameCutoff + '%');