How do I use a SELECT ... AS in a WHERE clause - sql

Question

Here is a piece of SQL code that does not work:
SELECT bl.regn_id,
RTRIM(LTRIM(dv.dv_id)) + '_' + RTRIM(LTRIM(bl.regn_id)) AS bu_regn,
(SELECT COUNT (em.em_id)
FROM em
LEFT OUTER JOIN bl bl_s ON em.bl_id = bl_s.bl_id
LEFT OUTER JOIN irs_self_cert_em ON em.em_id = irs_self_cert_em.em_id
WHERE dv.dv_id = em.dv_id
AND bl.bl_id = bl_s.bl_id
AND irs_self_cert_em.date_cert_loc >= DATEADD(month, -1, GETDATE())
AND (em.date_last_update_cads >= (select date_last_update_completed FROM ddi_completed WHERE ddi_id='TRA_CADS_EM'))
) AS certified
FROM bl
CROSS JOIN dv
WHERE bl.status = 'A' AND (certified > 0 )
I receive the error: "Lookup Error - SQL Server Database Error: Invalid column name 'certified'."
As you can see I use a subquery within the SELECT statement and give it the name 'certified'. I then try to use that value in the WHERE clause.
Can someone suggest and alternative way of accomplishing this?
Many thanks,
Matt

Answer 1

You can not use an aliased (calculated) column in a WHERE clause. I would create another subquery to add criteria to that field.
SELECT * FROM
(
SELECT
bl.regn_id,
RTRIM(LTRIM(dv.dv_id)) + '_' + RTRIM(LTRIM(bl.regn_id)) AS bu_regn,
(
SELECT
COUNT(em.em_id) AS [Count]
FROM
em LEFT OUTER JOIN bl AS bl_s
ON
em.bl_id = bl_s.bl_id LEFT OUTER JOIN irs_self_cert_em
ON
em.em_id = irs_self_cert_em.em_id
WHERE
dv.dv_id = em.dv_id
AND
bl.bl_id = bl_s.bl_id
AND
irs_self_cert_em.date_cert_loc >= DATEADD(month, -1, GETDATE())
AND
(em.date_last_update_cads >= (select date_last_update_completed FROM ddi_completed WHERE ddi_id='TRA_CADS_EM'))
) AS certified
FROM
bl CROSS JOIN dv
WHERE
bl.status = 'A'
) AS temp
WHERE
certified > 0
I also tried to clean up the query a bit. You were using LEFT OUTER JOINs with criteria on the right had side table, so it was truly an INNER JOIN (INNER JOINs will work more efficiently / quickly). Check it out and let me know if this works for you as expected.
;WITH
cte AS
(
SELECT
bl.regn_id,
RTRIM(LTRIM(dv.dv_id)) + '_' + RTRIM(LTRIM(bl.regn_id)) AS bu_regn
COUNT(*) OVER (PARTITION BY bl.regn_id, dv.dv_id, bl.regn_id ORDER BY bl.regn_id) AS [Certified]
FROM
dv INNER JOIN em
ON
dv.dv_id = em.dv_id INNER JOIN JOIN bl
ON
em.bl_id = bl.bl_id INNER JOIN JOIN irs_self_cert_em
ON
em.em_id = irs_self_cert_em.em_id
WHERE
bl.status = N'A'
AND
irs_self_cert_em.date_cert_loc >= DATEADD(month, -1, GETDATE())
AND
(em.date_last_update_cads >= (select date_last_update_completed FROM ddi_completed WHERE ddi_id='TRA_CADS_EM')
)
SELECT
DISTINCT
*
FROM
cte
WHERE
Certified > 0

Answer 2

Without having tables structure (ex: to know which id is unique) some data related to them and the way you want the output, it's hard to say and test but I went with something that look like this :
SELECT bl.regn_id,
RTRIM(LTRIM(dv.dv_id)) + '_' + RTRIM(LTRIM(bl.regn_id)) AS bu_regn,
result.certified
FROM bl
INNER JOIN
(SELECT em.bl_id AS bl_id, COUNT (em.em_id) as certified
FROM em
LEFT OUTER JOIN bl bl_s ON em.bl_id = bl_s.bl_id
INNER JOIN irs_self_cert_em ON em.em_id = irs_self_cert_em.em_id
AND irs_self_cert_em.date_cert_loc >= DATEADD(month, -1, GETDATE())
GROUP BY em.bl_id
HAVING COUNT (em.em_id) > 0
) AS result ON result.bl_id = bl.bl_id
INNER JOIN em ON result.bl_id = em.bl_id
AND (em.date_last_update_cads >=
(SELECT date_last_update_completed FROM ddi_completed WHERE ddi_id='TRA_CADS_EM'))
CROSS JOIN dv ON dv.dv_id = em.dv_id
WHERE bl.status = 'A'

Answer 3

SELECT bl.regn_id,
RTRIM(LTRIM(dv.dv_id)) + '_' + RTRIM(LTRIM(bl.regn_id)) AS bu_regn,
S.certified
FROM bl
CROSS JOIN dv
CROSS APPLY (SELECT COUNT (em.em_id) as certified
FROM em
LEFT OUTER JOIN bl bl_s ON em.bl_id = bl_s.bl_id
LEFT OUTER JOIN irs_self_cert_em ON em.em_id = irs_self_cert_em.em_id
WHERE dv.dv_id = em.dv_id
AND bl.bl_id = bl_s.bl_id
AND irs_self_cert_em.date_cert_loc >= DATEADD(month, -1, GETDATE())
AND (em.date_last_update_cads >= (select date_last_update_completed FROM ddi_completed WHERE ddi_id='TRA_CADS_EM'))
) AS S
WHERE bl.status = 'A' AND (S.certified > 0 )