3个表的内部联接查询

Question

I don't know what is wrong here. I am running a query with a multiple join of 3 tables, the query below works perfectly... Giving me the employee details, his age, if he requires the certificate and gives me info regarding the certificates expiry date, also puts a "-" in the next field if a certificate is not required - and as I said, this works like a charm...

    SELECT 
    `employee`.*,
    date_format(now(), '%Y') - date_format(`empl_dob`, '%Y') - 
      (date_format(now(), '00-%m-%d') < date_format(`empl_dob`, '00-%m-%d')) AS age,
    `certs`.`cert_medical_restrict`, 
    IF( `jobtitle`.`jt_medical`='n/a', `jobtitle`.`jt_medical`, 
        IF( `certs`.`cert_medical` = 0, 'No Cert',
             IF( (DATEDIFF((DATE_ADD(`certs`.`cert_medical`, INTERVAL 365 DAY)),CURDATE())) < 1, 'X', 
                IF( (DATEDIFF((DATE_ADD(`certs`.`cert_medical`, INTERVAL 365 DAY)),CURDATE())) < 30, 'ES', 'ok')))
        ) AS medical,       
    IF( `jobtitle`.`jt_medical`='n/a', '-', 
        IF( `certs`.`cert_medical` = 0, '-', (DATEDIFF((DATE_ADD(`certs`.`cert_medical`, INTERVAL 365 DAY)),CURDATE())))) AS medicalx   
    FROM `employee` 
    JOIN `jobtitle` 
    ON `employee`.`jobtitle_id` = `jobtitle`.`jobtitle_id` 
    JOIN `certs` 
    ON `certs`.`empl_idno` = `employee`.`empl_idno` 
    WHERE `employee`.`empl_no` = '10517602'

...But for my next query, I need to display the actual expiry date of the certificate, the queries look very much the same, but without the extra IF statements...

    SELECT 
    `employee`.*,
    date_format(now(), '%Y') - date_format(`empl_dob`, '%Y') - 
       (date_format(now(), '00-%m-%d') < date_format(`empl_dob`, '00-%m-%d')) AS age,
    `certs`.`cert_medical_restrict`, 
    IF( `jobtitle`.`jt_medical`='n/a', `jobtitle`.`jt_medical`, 
        IF( `certs`.`cert_medical` = 0, 'No Cert', (DATE_ADD(`certs`.`cert_medical`, INTERVAL 365 DAY)))) AS medical,       
    IF( `jobtitle`.`jt_medical`='n/a', '-', 
        IF( `certs`.`cert_medical` = 0, '-', (DATEDIFF((DATE_ADD(`certs`.`cert_medical`, INTERVAL 365 DAY)),CURDATE())))) AS medicalx   
    FROM `employee` 
    JOIN `jobtitle` 
    ON `employee`.`jobtitle_id` = `jobtitle`.`jobtitle_id` 
    JOIN `certs` 
    ON `certs`.`empl_idno` = `employee`.`empl_idno` 
    WHERE `employee`.`empl_no` = '10517602'

Now I get this error "Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (utf8mb4_general_ci,COERCIBLE) for operation 'if' " I cannot get my head around it, I have checked to see if the three tables differ from each other, but all are set to "latin_swedish_ci"

What am I doing wrong here? Any help would be appreciated - thanx

Answer 1

IMPLICIT is about inSQL strings, not about some database fields.
Using utf8 everywhere should fix all this issues..

Read this article about this issue.