Use CASE in Select Statement

Question

I would expect the query below to name the case column according to the date range - however all are defaulting to error - what am I missing? It has been quite sometime since I have worked in mySQL. I am trying to group based on the intervals overdue, today, tomorrow, 30 days, 60 days, 90 days.

    SELECT DATE_SUB(CURDATE(), INTERVAL 1 DAY)AS rDate,

    CURDATE()AS rDate,DATE_ADD(CURDATE(), INTERVAL 1 DAY)AS rDate,

    DATE_ADD(CURDATE(), INTERVAL 7 DAY)AS rDate,

    DATE_ADD(CURDATE(), INTERVAL 14 DAY)AS rDate,

    DATE_ADD(CURDATE(), INTERVAL 30 DAY)AS rDate,

    DATE_ADD(CURDATE(), INTERVAL 60 DAY)AS rDate,

    DATE_ADD(CURDATE(), INTERVAL 90 DAY)AS rDate,

    CASE a.nextDueDate

    WHEN a.nextDueDate < CURDATE() THEN 'Overdue'

    WHEN a.nextDueDate > CURDATE() AND a.nextDueDate < (DATE_ADD(CURDATE(), INTERVAL 7 
    DAY))THEN '7 Days'

    WHEN a.nextDueDate > CURDATE() AND a.nextDueDate < (DATE_ADD(CURDATE(), INTERVAL 
    14 DAY))THEN '15 Days'

    WHEN a.nextDueDate > CURDATE() AND a.nextDueDate < (DATE_ADD(CURDATE(), INTERVAL 30 DAY))THEN '30 Days'

    WHEN a.nextDueDate > CURDATE() AND a.nextDueDate < (DATE_ADD(CURDATE(), INTERVAL 60 DAY))THEN '60 Days'

    WHEN a.nextDueDate > CURDATE() AND a.nextDueDate < (DATE_ADD(CURDATE(), INTERVAL 90 DAY))THEN '90 Days'

    ELSE 'Error'

    END,

    g.groupId,g.name AS groupName,l.logId,l.name AS logName, i.itemID,

    i.name AS itemName, le.userName,completed, i.optimalMin,i.optimalMax ,le.value,

    u.name AS unitDescription,

    g1.parentId AS parentId1, g1.name AS group1Name,g2.parentId AS parentId2, g2.name 
    AS group2Name,

    g3.parentId AS parentId3, g3.name AS group3Name,

    a.name AS activityName,scheduleType,scheduleInterval,a.details,nextDueDate

    FROM logExceptions le

    INNER JOIN logs l ON l.logID = le.logID

    INNER JOIN groups g ON g.groupId = l.groupId

    INNER JOIN items i ON le.itemId = i.itemId

    INNER JOIN activities a ON l.logId = a.logId

    LEFT JOIN units u ON i.unitId = u.unitId

    LEFT JOIN groups g1 ON g.parentId = g1.groupId

    LEFT JOIN groups g2 ON g1.parentId = g2.groupId

    LEFT JOIN groups g3 ON g2.parentId = g3.groupId

    WHERE  nextDueDate IS NOT NULL

Answer 1

Remove a.nextDueDate from after the CASE keyword.

The CASE expression comes in two forms:

CASE <expression>
    WHEN <test-value1> THEN <result-value1>
    WHEN <test-value2> THEN <result-value2>
    ...
    ELSE <else-value>
END

In this form, the value of <expression> is compared against each <test-valueN> , and when it matches, the corresponding <result-valueN> is returned. If none match, the <else-value> is returned. This form is analogous to switch or case statements in other programming languages.

The other form is:

CASE WHEN <test-expression1> THEN <result-value1>
     WHEN <test-expression2> THEN <result-value2>
     ...
     ELSE <else-value>
END

In this case, each <test-expressionN> is evaluated, and if when one is true the corresponding <result-valueN> is returned. If none are true, the <else-value> is returned. This is analogous to if/then/elseif/else in other programming languages.

Since you're using the latter type of CASE , you shouldn't have an expression right after CASE .