For loop arrays with AND operators

Question

Having trouble getting code below to work. The idea is to loop through 3 arrays parallelly and per iteration get 3 values to insert in database.

The insertion works, but the loops never end and inserts duplicate rows.

How should this be done?

/Paul

readarray rows1 < /tmp/tempfile1
readarray rows2 < /tmp/tempfile2
readarray rows3 < /tmp/tempfile3

for i in "${rows1[@]}"; do
    for j in "${rows2[@]}"; do
            for k in "${rows3[@]}"; do

mysql --user=$DB_USER --password=$DB_PASSWD $DB_NAME << EOF
INSERT INTO $TABLE (\`column1\`,\`column2\`,\`column3\`) VALUES ("$i","$j","$k");
EOF

done
done
done

Nested loops are for cartesian products, not parallel loops. — Barmar, Oct 28 '21 at 20:42
Tangentially, you want `readarray -t` otherwise you'll keep the newlines. — glenn jackman, Oct 28 '21 at 20:44
This is calling mysql `n1 * n2 * n3` times. You'd be much better served building up a string (or file) containing all the inserts, and then you can invoke mysql once. — glenn jackman, Oct 28 '21 at 20:46
See ["Iterate over two arrays simultaneously in bash"](https://stackoverflow.com/questions/17403498/iterate-over-two-arrays-simultaneously-in-bash) (you have three, but the same principle applies). — Gordon Davisson, Oct 28 '21 at 20:48

score 3 · Answer 1 · answered Oct 28 '21 at 20:48

Loop over the array indexes, and use that to index all 3 arrays.

for index in "${!row1[@]}"; do
    i=${row1[index]}
    j=${row2[index]}
    k=${row3[index]}
    echo "INSERT INTO $TABLE (\`column1\`,\`column2\`,\`column3\`) VALUES ('$i','$j','$k');"
done | mysql --user=$DB_USER --password=$DB_PASSWD $DB_NAME

It might be better to create a CSV file from your input files, and use that with LOAD DATA INFILE, rather than doing a separate INSERT for each row.

For loop arrays with AND operators

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