fetch datas from two tables and differentiate between them - mysql

Question

I have two tables and want displays rows from the two one in the same page ordered by date created.
Here my query:
SELECT R.*, R.id as id_return
FROM return R
UNION
ALL
SELECT A.*, A.id as id_buy
FROM buy A
WHERE
R.id_buyer = '$user' AND R.id_buyer = A.id_buyer AND (R.stats='1' OR R.stats='3') OR A.stats='4'
ORDER
BY R.date, A.date DESC LIMIT $from , 20
With this query i get this error message:
Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in ...
And here how i think i can differentiate between the results: (Knowing if the result is from the table RETURN or from the table BUY)
if(isset($hist_rows["id_return"])) {
// show RETURN rows
} else {
// show BUY rows
}
Please what is wrong with the query, and if the method to differentiate between tables are correct ?
EDIT
Here my tables sample:
CREATE TABLE IF NOT EXISTS `return` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`id_buyer` INT(12) NOT NULL,
`id_seller` INT(12) NOT NULL,
`message` TEXT NOT NULL,
`stats` INT(1) NOT NULL,
`date` varchar(30) NOT NULL,
`update` varchar(30)
PRIMARY KEY (`id`)
)
CREATE TABLE IF NOT EXISTS `buy` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`id_buyer` INT(12) NOT NULL,
`product` INT(12) NOT NULL,
`title` VARCHAR(250) NOT NULL,
`stats` INT(1) NOT NULL,
`date` varchar(30) NOT NULL
PRIMARY KEY (`id`)
)

Answer 1

Be sure the two table return and buy have the same number (and type sequence) of colummns .. if not the query fails
try select only the column you need from both the table and be sure that these are in correspondenting number and type
SELECT R.col1, R.col2, R.id as id_return
FROM return R
UNION ALL
SELECT A.col1, A.col2, A.id as id_buy
FROM buy A
WHERE
........
Looking to your code you should select the same number and type of column form boith the table eg de sample below:
(where i have added the different column and selecting null from the table where are not present)
I have aslore referred the proper where condition to each table ..
SELECT
R.'from return' as `source_table`
, R.`id`
, R.`id_buyer`
, null as product
, null as title
, R.`id_seller` as id_seller
, R-`message`
, R.`stats`
, R.`date`
, R.`update`
FROM return R
WHERE R.id_buyer = '$user'
AND (R.stats='1' OR R.stats='3')
UNION ALL
SELECT
A.'from buy'
, A.`id`
, A.`id_buyer`
, A.`product`
, A.`title`
, null
, null
, A.`stats`
, A.`date`
, null
FROM buy A
WHERE
A.id_buyer = '$user'
AND A.stats='4'
ORDER BY `source table`, date DESC LIMIT $from , 20
for retrive te value of the first column you should use in your case
echo $hist_rows["source_table"];
Otherwise i the two table are in some way related you should look at a join (left join) for link the two table and select the the repated column
(but this is another question)
But if you need left join you can try
SELECT
R.`id`
, R.`id_buyer`
, R.`id_seller` as id_seller
, R-`message`
, R.`stats`
, R.`date`
, R.`update`
, A.`id`
, A.`id_buyer`
, A.`product`
, A.`title`
, null
, null
, A.`stats`
, A.`date`
FROM return R
LEFT JOIN buy A ON R.id_buyer = A.id_buyer
AND R.id_buyer = '$user'
AND (R.stats='1' OR R.stats='3')
AND A.stats='4'
ORDER BY R.date DESC LIMIT $from , 20

Answer 2

When you use union all, the queries need to have exactly the same columns in the same order. If the types are not quite the same, then they are converted to the same type.
So, you don't want union all. I'm guessing you want a join. Something like this:
SELECT r.co1, r.col2, . . ., r.id as id_return,
b.col1, b.col2, . . ., b.id as id_buy
FROM return r JOIN
buy b
ON r.id_buyer = b.id_buyer
WHERE r.id_buyer = '$user' and
(r.stats in (1, 3) OR A.stats = 4)
ORDER BY R.date, A.date DESC
LIMIT $from, 20;
This query is only a guess as to what you might want.

Answer 3

Since you're using a union, select a string that you set identifying each query:
SELECT 'R', R.*, R.id as id_return
FROM return R
UNION
ALL
SELECT 'A', A.*, A.id as id_buy
This way your string 'R' or 'A' is the first column, showing you where it came from. We can't really know why it's failing without the full query, but I'd guess your $from might be empty?
As for your
Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, boolean given in ...
Run the query directly first to get the sql sorted out before putting it into your PHP script. The boolean false indicates the query failed.