更新所有表记录及其来自另一个表的相应数据

Question

the thing is, i have a table students table and another scores table and i already have all the students in the scores table but the class field is still empty so, i thought i could update all of them with the data from the the students table. each students with his/her class.

UPDATE scores_tbl
    INNER JOIN students_tbl
        ON scores_tbl.reg_id = students_tbl.reg_id
    SET scores_tbl.class = IF(students_tbl.class > 0, students_tbl.class, scores_tbl.class) 
WHERE scores_tbl.session ="2018/2019";

am displayed with: Truncated incorrect DOUBLE value

Answer 1

try this

UPDATE scores_tbl
    INNER JOIN students_tbl
        ON scores_tbl.reg_id = students_tbl.reg_id
    SET scores_tbl.class = IF(IFNULL(students_tbl.class, 0) > 0, IFNULL(students_tbl.class, 0), IFNULL(scores_tbl.class, 0)) 
WHERE scores_tbl.session ="2018/2019";

Answer 2

You may try this. Since you only want to update the record if student_tbl.class has any value. It is better to write this condition in where clause and simplify your query.

UPDATE scores_tbl
    INNER JOIN students_tbl
        ON scores_tbl.reg_id = students_tbl.reg_id
    SET scores_tbl.class = students_tbl.class 
WHERE scores_tbl.session ="2018/2019" and cast(students_tbl.class as int) > 0;

I am expecting that class column has only integer values.