I have a query that works well, where i would like an assistance is how to incorporate a condition to determine the value displayed on a given column. That is if a column of a table has a value say "Authorization of COA" then the column date added should show the date else the column should show null
Here is my query so far
SELECT r.request_id, r.product_name, r.created_at, r.can,a_s.stat, r.client_id, CONCAT(u.fname,' ',u.lname) 'analyst' , t.date_added (//should show the value of date_added else NULL based on a condition for this column),
FROM request r
LEFT OUTER JOIN assigned_samples a_s ON r.request_id = a_s.labref
LEFT OUTER JOIN user u ON a_s.analyst_id = u.id
LEFT OUTER JOIN tracking_table t ON r.request_id = t.labref
WHERE r.client_id='$cid'
AND r.created_at BETWEEN '$start' AND '$end'
AND a_s.department_id = '$dept'
GROUP BY r.request_id
ORDER BY `r`.`created_at` DESC "
A simple CASE statement should be sufficient in this case, I believe.
SELECT r.request_id, r.product_name, r.created_at, r.can,a_s.stat, r.client_id,
CONCAT(u.fname,' ',u.lname) 'analyst',
CASE WHEN ConditionColumn = 'Authorization of COA' THEN t.date_added
ELSE NULL END AS 'date_added'
FROM request r
LEFT OUTER JOIN assigned_samples a_s ON r.request_id = a_s.labref
LEFT OUTER JOIN user u ON a_s.analyst_id = u.id
LEFT OUTER JOIN tracking_table t ON r.request_id = t.labref
WHERE r.client_id='$cid'
Give this a try:
SELECT r.request_id, r.product_name, r.created_at, r.can,a_s.stat, r.client_id, CONCAT(u.fname,' ',u.lname) 'analyst' ,
IFF(nameOfColumnToTest = 'Authorization of COA', t.date_added, null) AS DateAdded
FROM request r
LEFT OUTER JOIN assigned_samples a_s ON r.request_id = a_s.labref
LEFT OUTER JOIN user u ON a_s.analyst_id = u.id
LEFT OUTER JOIN tracking_table t ON r.request_id = t.labref
WHERE r.client_id='$cid'
AND r.created_at BETWEEN '$start' AND '$end'
AND a_s.department_id = '$dept'
GROUP BY r.request_id
ORDER BY `r`.`created_at` DESC "
In both mysql and ms sql you can use case expression ( mysql case ; ms sql case ) to assign value to a field conditionally:
SELECT r.request_id, r.product_name, r.created_at, r.can,a_s.stat, r.client_id, CONCAT(u.fname,' ',u.lname) 'analyst' ,
CASE WHEN Column_To_Test = 'Authorization of COA' THEN t.date_added
ELSE null
END AS date_added
FROM request r
LEFT OUTER JOIN assigned_samples a_s ON r.request_id = a_s.labref
LEFT OUTER JOIN user u ON a_s.analyst_id = u.id
LEFT OUTER JOIN tracking_table t ON r.request_id = t.labref
WHERE r.client_id='$cid'
AND r.created_at BETWEEN '$start' AND '$end'
AND a_s.department_id = '$dept'
GROUP BY r.request_id
ORDER BY `r`.`created_at` DESC "
This way the solution is more portable between the databases. Mysql offers if() function, ms sql iif() to achieve the above, but those are product specific solutions.
Try to use the Case statements like.
CASE WHEN ( Condition_1 AND Condition_2 OR ... Condition_N ) THEN (Value_1) ELSE (Value_1) END
Here Condition _1 can be column record value and its combination of Column record values and Value _1 can be single value [Ex: Null or "some string"] or Returned value from nested sql statement like [Ex: (select count(*) from ...)]
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