How do I write the following mySQL query? - mysql

Question

I have a database in the following format:
idA | idB | stringValue
----+-----+------------
xyz | 1 | ANDFGFRDFG
xyz | 2 | DTGDFHFGH
xyz | 3 | DFDFDS
abc | 5 | DGDFHHGH
abc | 6 | GG
...
idA and idB together are unique.
I have a file (list.txt) with a list of id pairs like this:
xyz 2
abc 5
abc 6
...
and I would like to print it with stringValue in each row. Note some pairs of ids from the file might be absent from the DB. In that case, I don't want to print them at all.
In short, I want to filter a table using a file.

Answer 1

SELECT idA, idB, stringValue FROM table WHERE idA = 'xyz' AND idB = 12;
Would give you all columns where idA equals "xyz" and idB equals 12.

Answer 2

The number of OR clauses will be dynamic based on the number of combinations in your file.
You will probably need to make this a dynamically created query on the lines of
SELECT * FROM myTable
WHERE
(idA = 'xyz'AND idB = '2')
OR
(idA = 'abc'AND idB = '5')
OR
(idA = 'abc'AND idB = '6')
......

Answer 3

Some SQL clients do provide the facility that allow you to create queries or data straight from files. However I believe the better approach would be to write a script for this.
Based on other questions you recently gave like this one then perhaps the solution below in Perl may help you:
use 5.012;
use warnings;
use SQL::Abstract;
my $sql = SQL::Abstract->new;
my #cols = qw/ idA idB stringValue /;
my $where = build_sql_where_from_file( 'list.txt', #cols[0,1] );
my ($query, #bind) = $sql->select(
'yourTable',
\#cols,
$where,
);
sub build_sql_where_from_file {
my $file = shift;
my #build;
open my $fh, '<', $file or die $!;
for my $line (<$fh>) {
chomp $line;
my #fields = split / /, $line;
push #build, {
-and => [
map { $_ => shift #fields } #_,
]
};
}
return \#build;
}
If I now do the following using your example list.txt...
say $query;
say join ":", #bind;
then I get:
SELECT idA, idB, stringValue FROM yourTable WHERE ( ( ( idA = ? AND idB = ? ) OR ( idA = ? AND idB = ? ) OR ( idA = ? AND idB = ? ) ) )
xyz:2:abc:5:abc:6
Which is exactly what I need to then plugin straight into a DBI query.
Hope that helps.
/I3az/