select rows where same column values start with string, 2 questions - php

Question

I'm trying to get multiple sums of rows, each sum has a matching column string value, and all the values have a matching 4 character prefix, but it's not working and I could use some help. Also, would CASE be a more or less costly query on the db?
Started with this:
$sql =
"SELECT col1
FROM table
WHERE substr(col1,1,5)='$string'";
$query = mysqli_query($con, $sql);
$row = mysqli_fetch_array($query,MYSQLI_ASSOC);
$results = $row['col1'];
$sum1 = count(array_keys($results,'string1'));
$sum2 = count(array_keys($results,'string2'));
Does it work to get the results from the same column that's in the WHERE clause?
In practice, col1 has row values like aaaa_string1, aaaa_string1, aaaa_string2, aaaa_string2, bbbb_string8... so I'm looking to get all col1 results that have the aaaa in an array, then subsequently filter how many exist of each string1 and string2.

Answer 1

Use SUBSTR(col1, LENGTH('$string')+1) to get the part of the column after the prefix, and group by this.
Use LIKE 'prefix%' to match a column beginning with a prefix.
SELECT SUBSTR(col1, LENGTH('$string')+1) AS suffix, COUNT(*) as count
FROM table
WHERE col1 LIKE '$string%'
GROUP BY suffix
Then you can use a loop to create an associative array with all the counts:
$counts = array();
while ($row = mysqli_fetch_assoc($query) {
$counts[$row['suffix']] = $row['count'];
}
var_dump($counts);

Answer 2

Looking at you code seems that you are trying to get the cout for substring 'string1' or 'string2' in col1
"select col1, count(*) as col_count
from table
WHERE substr(col1,1,5)= '$string'
and col1 in ('string1','string2')
group by col1"
You should retrive the result in col_string and col_count
for suffix (assuming char 6 to end)
"select bstr(col1, 6, 100), count(*) as col_count
from table
WHERE substr(col1,1,5)= '$string'
and substr(col1, 6, 100) in ('string1','string2')
group by bstr(col1, 6, 100)"