Finds number which have same last digit from 2 different columns - sql

Question

I have 2 columns of phone number and the requirement is to get the numbers which have same last 8 digits. ColumnA's numbers have 11 digits and columnB's numbers have 9 or 10 digits.
I tried to use SUBSTR or LIKE and LEFT RIGHT function to solve but the problem is the data is too big and i can't use that way.
select trunc(ta.timeA), ta.columnA
from table1A ta,
tableB tb
WHERE substr(ta.columnA,-8) LIKE substr(tb.columnB,-8)
and trunc(ta.timeA) = trunc(ta.timeB)
AND trunc(ta.timeA) >= TO_DATE('01/01/2018', 'dd/mm/yyyy')
AND trunc(ta.timeA) < TO_DATE('01/01/2018', 'dd/mm/yyyy') + 1
GROUP BY ta.columnA, trunc(ta.timeA)

Answer 1

You want to select from tableA, so do this. Don't join. You only want to select tableA rows that have a match in tableB. So place an EXISTS clause in your WHERE clause.
select trunc(timea), columna
from table1a ta
where trunc(timea) >= date '2018-01-01'
and trunc(timea) < date '2018-01-02'
and exists
(
select *
from tableb tb
where trunc(tb.timeb) = trunc(ta.timea)
and substr(tb.columnb, -8) = substr(ta.columna, -8)
)
order by trunc(timea), columna;
In order to have this run fast, create the following indexes:
create idxa on tablea( trunc(timea), substr(columna, -8) );
create idxb on tableb( trunc(timeb), substr(columnb, -8) );
I don't see, however, why you are so eager to have this run fast. Do you want to keep all data as is and run the query again and again? There should be a better solution. Splitting the area code and number into two separate columns is the first thing that comes to mind.
UPDATE: Still faster than the suggested idxa should be a covering index for tableA:
create idxa on tablea( trunc(timea), substr(columna, -8), columna );
Here the DBMS can work with the index only and doesn't have to access the table. So just in case the above was still a bit too slow for you, you can try with this altered index.
And as Alex Poole has pointed out in the comments below, it should be
where trunc(timea) = date '2018-01-01'
only, if the range you are looking at is always a single day as in the example.

Answer 2

You can try below using = operator instead of like operator
as your want to match last 2 digit
select trunc(ta.timeA),ta.columnA
from table1A ta inner join tableB tb
on substr(ta.columnA,-8) = substr(tb.columnB,-8)
and trunc(ta.timeA) = trunc(ta.timeB)
AND trunc(ta.timeA) >= TO_DATE('01/01/2018', 'dd/mm/yyyy')
AND trunc(ta.timeA) < TO_DATE('01/01/2018', 'dd/mm/yyyy') + 1
GROUP BY ta.columnA, trunc(ta.timeA)

Answer 3

It would be easier to help if you were more specific about your SQL environment, below is some advice on this query that would apply in most environments.
When dealing with large data sets performance becomes even more critical and small changes in technique can have a big impact.
For example:
Like is normally used for a partial match with wildcards, do you not mean equals? Like is slower than equals, if you're not using wildcards I recommend looking for equality.
Also, you initially start with a (cross/cartesian product) join, but then your where clause defines very specific match criteria (matching time fields), if you need a matching time field make it part of the table join, this will reduce the number of join results which will significantly shrink the dataset that then needs to have the other criteria applied to it.
Also, having date calculated values in your where clause is slow. It is better to set a #fromDate and #toDate parameter before the query, then use these in the where clause as what are then literals which then don't need to be calculated for every row.