Join column names from Tab1 with 1 column values of Tab2 - php

Question

I have 2 tables with the following structures:
// tab1:
| ID | Col1 | Col2 | Col3 | Col4 |
|----|------|------|------|------|
| 1 | Val1 | Val2 | Val3 | Val4 |
| 2 | Val5 | Val6 | Val7 | Val8 |
// tab2:
| Name |
|------|
| Col1 |
| Col3 |
I now need to get all values from tab1 and somehow join them with the values of the column of tab2, so that in the frontend all columns from tab1, that are also present in tab2, are bold.
In pseudocode it would look like that:
SELECT Col1, COl2, Col3, Col4 FROM tab1, tab2 WHERE ID=1 AND {possibly a left join on tab2}
The desired output as a table in the fronted could be:
Value 1: Val1
Value 2: Val2
Value 3: Val3
Value 4: Val4
Since col1 and col3 are also in tab2, their values should be bold.
So I just need the appropriate query with a "flag". In the frontend I then would just loop the results and look for the flag. If the flag is set, display the value as bold.
I don't really have influence on the database structure.

Answer 1

Assuming that the table structure is complete and we know all the column names, we can execute the below query to check whether a value exists or not.
select col1 as col1 ,
(select count(*) from tab2 where name = 'col1') col1_exists,
col2 as col2,
(select count(*) from tab2 where name = 'col2') col2_exists,
col3 as col3 ,
(select count(*) from tab2 where name = 'col1') col3_exists
from tab1;
For non zero 'exists' values, we can show the corresponding column value in bold. Here is the SQL Fiddle.

Answer 2

Try this :
SELECT
t.`VALUE`,
(CASE WHEN tab2.Name IS NULL THEN 0 ELSE 1 END) flag
FROM
(
SELECT
Col1 AS `VALUE`,
'Col1' AS colNum
FROM tab1
WHERE ID = 1
UNION
SELECT
Col2 AS `VALUE`,
'Col2' AS colNum
FROM tab1
WHERE ID = 1
UNION
SELECT
Col3 AS `VALUE`,
'Col3' AS colNum
FROM tab1
WHERE ID = 1
UNION
SELECT
Col4 AS `VALUE`,
'Col4' AS colNum
FROM tab1
WHERE ID = 1
) t
LEFT JOIN tab2
ON tab2.`Name` = t.colNum;
SQL FIDDLE

Answer 3

Due to the restrictions with your design, you are not able to do this with MYSQL alone, but you can with the help of PHP:
get the column names from tbl2
use those column names to obtain your results from tbl1
Try the following (assuming you use mysqli):
//get columns from tbl2
$sql = 'SELECT * FROM tbl2';
$result = mysqli_query($conn, $sql);
$cols = [];
while ($row = mysqli_fetch_assoc($result)) {
$cols[] = $row['name'];
}
//get results from tbl1 using column names
$sql = 'SELECT ' . implode(',', $cols) . ' FROM tbl1 WHERE ID=1';
$result = mysqli_query($conn, $sql);
while ($row = mysqli_fetch_assoc($result)) {
var_dump($row);
}