Mysql higher LIMIT offset very slow with join in PHP - php

Question

I'm trying to change mySQL query for a faster data retrieval from the server. I have a table with more than 500,000 records but it takes forever to retrieve the data.
I want to change the query from
SELECT
loanapply.loanapplyId,
loanapply.loanAmount,
loanapply.email,
loanapply.approve,
loanapply.loanDate,
mkopakenya.name,
mkopakenya.idno,
mkopakenya.phoneNo,
mkopakenya.verification
FROM
loanapply
LEFT JOIN mkopakenya ON loanapply.email = mkopakenya.email
WHERE
loanapply.approve = 'ongoing'
AND loanapply.del = 'false'
AND loanapply.archive = 0
AND loanapply.loanDate = '$date'
GROUP BY
loanapply.loanapplyId,
loanapply.loanAmount,
loanapply.email,
loanapply.approve,
loanapply.loanDate,
mkopakenya.name,
mkopakenya.idno,
mkopakenya.phoneNo,
mkopakenya.verification
ORDER BY
loanapplyId DESC
LIMIT
$currentSize,
$limit
to
SELECT
loanapply.loanapplyId,
loanapply.loanAmount,
loanapply.email,
loanapply.approve,
loanapply.loanDate,
mkopakenya.name,
mkopakenya.idno,
mkopakenya.phoneNo,
mkopakenya.verification
FROM
loanapply
LEFT JOIN mkopakenya ON loanapply.email = mkopakenya.email AS data1
INNER JOIN (
SELECT
loanapply.loanapplyId
FROM
loanapply
LIMIT
$currentSize,
$limit
) AS data2 ON data1.loanapplyId = data2.loanapplyId
WHERE
loanapply.approve = 'ongoing'
AND loanapply.del = 'false'
AND loanapply.archive = 0
AND loanapply.loanDate = '$date'
ORDER BY
loanapplyId DESC
for faster data retrieval, The second query only returns blank values

Answer 1

for fast data retrival first you should check for valid indexes
be sure you have a proper composite index on loanapply eg:
create index myidx on loanapply ( loanDate, archive, del, approve, email )
and
table mkopakenya column ( email)
anyway (not for better perfomance but for proper use of SQL) you should not use group by without aggregation function (this behaviour is allowed for mysql version <5.7 but, by default, produce error for version >= 5.7) if you need distinct result use DISTINCT clause
SELECT DISTINCT loanapply.loanapplyId
, loanapply.loanAmount
, loanapply.email
, loanapply.approve
, loanapply.loanDate
, mkopakenya.name
, mkopakenya.idno
, mkopakenya.phoneNo
, mkopakenya.verification
FROM loanapply
LEFT JOIN mkopakenya ON loanapply.email = mkopakenya.email
WHERE loanapply.approve='ongoing'
AND loanapply.del='false'
AND loanapply.archive=0
AND loanapply.loanDate='$date'
ORDER BY loanapplyId DESC LIMIT $currentSize, $limit