Apply if row exist function on left join - mysql

Question

I'm combining 3-6 tables using left join. Here's some example of the code on from clause
FROM ip_ucp_01
LEFT JOIN ip_lt_01
ON ip_ucp_01.time = ip_lt_01.time
AND ip_ucp_01.date = ip_lt_01.date
LEFT JOIN ip_le
ON ip_lt_01.time = ip_le.time
AND ip_lt_01.date = ip_le.date
LEFT JOIN ip_lmiv_01
ON ip_le.time = ip_lmiv_01.time
AND ip_le.date = ip_lmiv_01.date
LEFT JOIN ip_cwg
ON ip_lmiv_01.time = ip_cwg.time
AND ip_lmiv_01.date = ip_cwg.date
LEFT JOIN ip_mtu_01
ON ip_cwg.time = ip_mtu_01.time
AND ip_cwg.date = ip_mtu_01.date
if there is no row on second table and third table, the data forth table and so on won't be displayed. I need to check whether the row on second table is exist or not. If so, it will use left join second table, if not it will use left join on third table and so on.

Answer 1

How about if you just JOIN with your first table? Like this:
FROM ip_ucp_01
LEFT JOIN ip_lt_01
ON ip_ucp_01.time = ip_lt_01.time
AND ip_ucp_01.date = ip_lt_01.date
LEFT JOIN ip_le
ON ip_ucp_01.time = ip_le.time
AND ip_ucp_01.date = ip_le.date
LEFT JOIN ip_lmiv_01
ON ip_ucp_01.time = ip_lmiv_01.time
AND ip_ucp_01.date = ip_lmiv_01.date
LEFT JOIN ip_cwg
ON ip_ucp_01.time = ip_cwg.time
AND ip_ucp_01.date = ip_cwg.date
LEFT JOIN ip_mtu_01
ON ip_ucp_01.time = ip_mtu_01.time
AND ip_ucp_01.date = ip_mtu_01.date
since you only join on date and time won't this do what you want?

Answer 2

I don't think LEFT JOIN will work the way your are asking for ,because if there is no entry in parent table your won't be able to fetch data from grandchild .
In my opinion you can simple use CASE with Count (not best practice) but it will solve your problem.

Answer 3

You can use separate SELECT queries for those JOINs and UNION them all (with DISTINCT) into one query, e.g.:
SELECT DISTINCT column_name
FROM (
SELECT column_name
FROM ip_ucp_01
LEFT JOIN ip_lt_01 ON ip_ucp_01.time = ip_lt_01.time AND ip_ucp_01.date = ip_lt_01.date
LEFT JOIN ip_le ON ip_lt_01.time = ip_le.time AND ip_lt_01.date = ip_le.date;
UNION
SELECT column_name
FROM ip_ucp_01
LEFT JOIN ip_lmiv_01 ON ip_ucp_01.time = ip_lmiv_01.time AND ip_ucp_01.date = ip_lmiv_01.date
) a;