如何从mysql中的同一表创建基于树的查询？

Question

Hey guys i want to create one tree based data in my html view from mysql. I have one table salary_slip there 2 columns pay_month and pay_year .

data is like this:

pay_month      pay_year

February         2014
march            2014
January          2015
February         2015
April            2015
may              2015
June             2015
January          2016
march            2016
December         2016

So now i want to create tree view for the same.so, if user will click on 2016(pay_year) onclick this all data in pay_month in front of 2016 should be display in tree format and same for the all.

My current query is:

select 
    PAY_MONTH,
    PAY_YEAR 
from 
    india_salary_slip_details 
where 
    EMPLOYEE_ID = 34 
group by 
    pay_year 

By this i got my data: but i can only see each year's first month only. please provide me with better query so i can get my result.

image for the same: current data from my query

Answer 1

A major part of your problem comes from the use of GROUP BY , which is used for, well, grouping.

MySQL has different handling of GROUP BY than other DBMS' that require all non-aggregate fields to be listed in the GROUP BY clause. MySQL give you enough rope with which to hang yourself (so to speak), which is why you didn't get an error for what is clearly not an intended use of GROUP BY .

Depending on how your front end is handling the data, you have a few options.

Option 1) Have it load (ordered) and use the output loop to determine the change in year.

SQL Query:

SELECT 
    PAY_MONTH,
    PAY_YEAR 
FROM 
    india_salary_slip_details 
WHERE 
    EMPLOYEE_ID = 34 
ORDER BY 
    pay_year,
    pay_month -- we want it ordered by year, then month, though this will be alphabetical due to the data type

PHP Code:

<?php
$year = NULL;
foreach ($result as $row) { // Assuming your result is stored as $result
   if ($row['PAY_YEAR'] !== $year) {
       // Print the year in the left column so to speak, perhaps create a sublist, etc
       // Set the year 
       $year = $row['PAY_YEAR'];
   }
   // Add month
   // Do something with $row['PAY_MONTH'], perhaps add it to a sublist, again, depends on front end handling.
}

Option 2) Have it load the years, then the next level asynchronously.

SQL Query to get years:

SELECT DISTINCT
    PAY_YEAR 
FROM 
    india_salary_slip_details 
WHERE 
    EMPLOYEE_ID = 34 
ORDER BY
    PAY_YEAR

SQL Query to get months given a year:

SELECT 
    PAY_MONTH
FROM 
    india_salary_slip_details 
WHERE 
    EMPLOYEE_ID = 34 
    AND PAY_YEAR = (Whatever the year is)
ORDER BY 
    PAY_MONTH

Answer 2

The problem is your group by, you just want to order by year :

SELECT PAY_MONTH, PAY_YEAR, FROM india_salary_slip_details WHERE EMPLOYEE_ID = 34
ORDER BY PAY_YEAR