How I can create this SELECT query in MYSQL? - mysql

Question

I am having two MYSQL tables. These are named as :
attendance_summary, attendance_summary_cecb. Both tables have same fields but may have different data.
These are the result the month of August, 2016 from this two tables.
mysql> SELECT emp_id, date, days, ot_days, ot_hours FROM attendance_summary;
+--------+------------+------+---------+----------+
| emp_id | date | days | ot_days | ot_hours |
+--------+------------+------+---------+----------+
| 4 | 2016-08-01 | 10 | 0 | 20.0 |
| 4 | 2016-08-16 | 13 | 0 | 14.5 |
| 12 | 2016-08-01 | 12 | 0 | 10.0 |
| 12 | 2016-08-16 | 11 | 2 | 16.5 |
| 14 | 2016-08-01 | 12 | 2 | 15.0 |
| 14 | 2016-08-16 | 10 | 0 | 16.0 |
| 15 | 2016-08-01 | 11 | 0 | 16.0 |
| 15 | 2016-08-16 | 9 | 3 | 21.0 |
+--------+------------+------+---------+----------+
8 rows in set (0.00 sec)
mysql> SELECT emp_id, date, days, ot_days, ot_hours FROM attendance_summary_cecb;
+--------+------------+------+---------+----------+
| emp_id | date | days | ot_days | ot_hours |
+--------+------------+------+---------+----------+
| 4 | 2016-08-01 | 15 | 0 | 20.0 |
| 4 | 2016-08-16 | 10 | 0 | 12.0 |
| 12 | 2016-08-01 | 12 | 1 | 10.0 |
| 12 | 2016-08-16 | 11 | 2 | 16.5 |
| 14 | 2016-08-01 | 12 | 2 | 15.0 |
| 14 | 2016-08-16 | 10 | 0 | 16.0 |
| 15 | 2016-08-01 | 10 | 0 | 16.0 |
| 15 | 2016-08-16 | 9 | 0 | 21.0 |
+--------+------------+------+---------+----------+
8 rows in set (0.00 sec)
Using this two tables, In a single query, I need to get
> From `attendance_summary`
> - Total Days
> - Total OT Days
> - Total OT Hours
>
> From `attendance_summary_cecb`
> - Total Days
> - Total OT Days
> - Total OT Hours
This is how I tried it:
SELECT e.emp_id
, e.full_name
, MAX(days1) as days1
, MAX(ot_days1) as ot_days1
, MAX(ot_hours1) as ot_hours1
, MAX(days2) as days2
, MAX(ot_days2) as ot_days2
, MAX(ot_hours2) as ot_hours2
, SUM(days1+days2) AS olekma_days
, SUM(ot_days1+ot_days2) AS olekma_ot_days
, SUM(ot_hours1+ot_hours2) AS olekma_ot_hours
, SUM(days3+days4) AS cecb_days
, SUM(ot_days3+ot_days4) AS cecb_ot_days
, SUM(ot_hours3+ot_hours4) AS cecb_ot_hours
FROM
(
SELECT emp_id
, CASE DAY(date) WHEN 1 THEN days ELSE 0 END as days1
, CASE DAY(date) WHEN 1 THEN ot_days ELSE 0 END as ot_days1
, CASE DAY(date) WHEN 1 THEN ot_hours ELSE 0 END as ot_hours1
, CASE DAY(date) WHEN 16 THEN days ELSE 0 END as days2
, CASE DAY(date) WHEN 16 THEN ot_days ELSE 0 END as ot_days2
, CASE DAY(date) WHEN 16 THEN ot_hours ELSE 0 END as ot_hours2
FROM attendance_summary
WHERE MONTH(date) = 08 AND YEAR(date) = 2016
UNION
SELECT emp_id
, CASE DAY(date) WHEN 1 THEN days ELSE 0 END as days3
, CASE DAY(date) WHEN 1 THEN ot_days ELSE 0 END as ot_days3
, CASE DAY(date) WHEN 1 THEN ot_hours ELSE 0 END as ot_hours3
, CASE DAY(date) WHEN 16 THEN days ELSE 0 END as days4
, CASE DAY(date) WHEN 16 THEN ot_days ELSE 0 END as ot_days4
, CASE DAY(date) WHEN 16 THEN ot_hours ELSE 0 END as ot_hours4
FROM attendance_summary_cecb
WHERE MONTH(date) = 08 AND YEAR(date) = 2016
) as s
LEFT JOIN employees e USING (emp_id)
INNER JOIN categories c ON c.id = e.category_id AND c.salary_type = 'D'
WHERE e.category_id = 6
GROUP BY e.emp_id\G
UPDATE:
This is the table structure for these two tables:
CREATE TABLE `attendance_summary` (
`as_id` INT(11) NOT NULL AUTO_INCREMENT,
`emp_id` INT(11) NOT NULL,
`date` DATE NOT NULL DEFAULT '1901-01-01',
`days` INT(11) NOT NULL,
`ot_days` INT(11) NULL,
`ot_hours` DECIMAL(16,1) NULL,
PRIMARY KEY (`as_id`),
UNIQUE KEY (emp_id, `date`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
CREATE TABLE `attendance_summary_cecb` (
`as_id` INT(11) NOT NULL AUTO_INCREMENT,
`emp_id` INT(11) NOT NULL,
`date` DATE NOT NULL DEFAULT '1901-01-01',
`days` INT(11) NOT NULL,
`ot_days` INT(11) NULL,
`ot_hours` DECIMAL(16,1) NULL,
PRIMARY KEY (`as_id`),
UNIQUE KEY (emp_id, `date`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
But it doesn't work for me. Hope somebody may help me out.

Answer 1

The answer to your question is rather simple. Btw I had to create 2 missing tables from the bottom to confirm your error.
When you do a
select col1, col2 from t1
union
select col9 as fred, col11 as john from t2
or any variation on that theme with scads of tables, the only column names that come back are from the first member of the union.
In other words, fred and john don't come out.
So your days3 and days4 are not available coming out of the derived table s.
You need to rethink it then, but that answers the question :p
From the MySQL Manual Page entitled UNION Syntax:
The column names from the first SELECT statement are used as the
column names for the results returned. Selected columns listed in
corresponding positions of each SELECT statement should have the same
data type. (For example, the first column selected by the first
statement should have the same type as the first column selected by
the other statements.)