Related
I use Vertical SQL and have a field "Note" that is a free text field (no consistent way to enter data). I'd like to create another field with only dates or extract the last date in the field.
E.g
"1st order on 3/2/21, second 5/5/21" -> "3/2/21 5/5/21" or "5/5/21"
"first delivery 2/2/21 second one 8/30/21" -> "2/2/21 8/30/21" or "8/30/21"
"reported 1st: 2/2/21." -> "2/2/21"
Thanks!
You can use REGEXP_SUBSTR() to grab the patterns: one or more digits; slash; one or more digits; slash; one or more digits.
If you have more than one of those patterns, then, create one row as output for each pattern found. For that, CROSS JOIN with a consecutive series of integers, so you can output the n-th occurrence of the pattern. Then, cast the found string as DATE.
Finally, and only if you only need the last date, apply a Vertica-peculiar analytic limit clause , to only output the highest i value for the respective id (which I had to add) of the result table.
WITH
-- need a sequence of integers ...
i(i) AS (
SELECT 1
UNION ALL SELECT 2
UNION ALL SELECT 3
UNION ALL SELECT 4
)
,
indata(id,s) AS (
SELECT 1,'1st order on 3/2/21, second 5/5/21'
UNION ALL SELECT 2,'first delivery 2/2/21 second one 8/30/21'
UNION ALL SELECT 3,'reported 1st: 2/2/21.'
)
SELECT
id
, i
, s
, REGEXP_SUBSTR(s,'\d+/\d+/\d+',1,i) AS found_token
, REGEXP_SUBSTR(s,'\d+/\d+/\d+',1,i)::DATE AS found_date
FROM indata CROSS JOIN i
WHERE REGEXP_SUBSTR(s,'(\d+/\d+/\d+)',1,i,'',1) <>''
-- remove the following line if you want all dates from all strings
-- and keep it if you only want the last date in the string
LIMIT 1 OVER(PARTITION BY id ORDER BY i DESC)
;
id | i | s | found_token | found_date
----+---+------------------------------------------+-------------+------------
1 | 2 | 1st order on 3/2/21, second 5/5/21 | 5/5/21 | 2021-05-05
2 | 2 | first delivery 2/2/21 second one 8/30/21 | 8/30/21 | 2021-08-30
3 | 1 | reported 1st: 2/2/21. | 2/2/21 | 2021-02-02
Consistently is critical when parsing string data. If it will always end with a date preceded by a space, pulling the last date should be fairly simple. Consider:
Trim(Mid(Note, InStrRev(Note, " ")))
I have a wide table that looks like this:
Case REFERENCE
OUTCOME_EMP_SITUATION
MONTH1_EMP_SITUATION
MONTH1_REASON
MONTH3_EMP_SITUATION
MONTH3_REASON
MONTH6_EMP_SITUATION
MONTH6_REASON
12345
Employed
Employed
Outcome at 1 month
Employed
Outcome at 3 month
Employed
Outcome at 6 month
this is survey results that people completed after they finished employment program. They complete the survey 4 times, once immediately after finishing the program, and then after 1/3/6 month. the problem is, the results for immediately after program completion are in one table (Outcome table) and the 1/3/6 month checkpoint results are in another table (Checkpointinfo table) I would like to combine those tables to create a long table so that instead of having "Outcome" in 5 different columns, I would have it in one column and it would look like this:
Case Reference
Outcome_emp_situation
Month_Reason
12345
Employed
NULL
12345
Employed
Outcome at 1 month
12345
Employed
Outcome at 3 month
12345
Employed
Outcome at 6 month
I was wondering if anyone could please help me out to turn this wide query into a long table query.
Here is the query for the wide table:
Select
ch.CASEREFERENCE, oc.OUTCOME_DATE, oc.OUTCOME_REFERENCE_ID, oc.OUTCOME_EMP_SITUATION, oc.OUTCOME_EMPLOYMENT_TYPE, oc.OUTCOME_NUM_JOBS, oc.OUTCOME_NAICS_DESC, oc.OUTCOME_JOB_NATURE,
oc.OUTCOME_WORK_HOURS, oc.OUTCOME_WAGE, oc.OUTCOME_STUDENT_STATUS, oc.OUTCOME_GOT_SERVICE, oc.OUTCOME_RIGHT_SERVICE, oc.OUTCOME_RECOMMEND_PROGRAM,
ck1.REASONCODE AS REASONCODE1,
CASE WHEN ck1.REASONCODE = 'OT1' THEN "Outcome at 1 month" END MONTH1_REASON,
ck1.MONTH_START_DATE AS MONTH1_START_DATE, ck1.MONTH_END_DATE AS MONTH1_END_DATE, ck1.MONTH_OUTCOME_EMP_SITUATION AS MONTH1_OUTCOME_EMP_SITUATION,
ck1.MONTH_EMPLOYMENT_TYPE AS MONTH1_EMPLOYMENT_TYPE, ck1.MONTH_NUM_JOBS AS ,MONTH1_NUM_JOBS, ck1.MONTH_NAICS_DESC AS MONTH1_NAICS_DESC, ck1.MONTH_JOB_NATURE AS MONTH1_JOB_NATURE,
ck1.MONTH_WORK_HOURS AS MONTH1_WORK_HOURS, ck1.MONTH_WAGE AS MONTH1_WAGE, ck1.MONTH_STUDENT_STATUS AS MONTH1_STUDENT_STATUS, ck1.MONTH_GOT_SERVICE AS MONTH1_GOT_SERVICE,
ck1.MONTH_RIGHT_SERVICE AS MONTH1_RIGHT_SERVICE, ck1.MONTH_RECOMMEND_PROGRAM AS MONTH1_RECOMMEND_PROGRAM, ck1.MONTH_RESUBMIT_MILESTONE AS MONTH1_RESUBMIT_MILESTONE,
ck1.MONTH_MILESTONE_ACHIEVED AS MONTH1_MILESTONE_ACHIEVED, ck1.MONTH_APPROVED_DATE AS MONTH1_APPROVED_DATE,
ck3.REASONCODE AS REASONCODE3,
CASE WHEN ck3.REASONCODE = 'OT3' THEN "Outcome at 3 month" END MONTH3_REASON,
ck3.MONTH_START_DATE AS MONTH3_START_DATE, ck3.MONTH_END_DATE AS MONTH3_END_DATE, ck3.MONTH_OUTCOME_EMP_SITUATION AS MONTH3_OUTCOME_EMP_SITUATION,
ck3.MONTH_EMPLOYMENT_TYPE AS MONTH3_EMPLOYMENT_TYPE, ck3.MONTH_NUM_JOBS AS ,MONTH3_NUM_JOBS, ck3.MONTH_NAICS_DESC AS MONTH3_NAICS_DESC, ck3.MONTH_JOB_NATURE AS MONTH3_JOB_NATURE,
ck3.MONTH_WORK_HOURS AS MONTH3_WORK_HOURS, ck3.MONTH_WAGE AS MONTH3_WAGE, ck3.MONTH_STUDENT_STATUS AS MONTH3_STUDENT_STATUS, ck3.MONTH_GOT_SERVICE AS MONTH3_GOT_SERVICE,
ck3.MONTH_RIGHT_SERVICE AS MONTH3_RIGHT_SERVICE, ck3.MONTH_RECOMMEND_PROGRAM AS MONTH3_RECOMMEND_PROGRAM, ck3.MONTH_RESUBMIT_MILESTONE AS MONTH3_RESUBMIT_MILESTONE,
ck3.MONTH_MILESTONE_ACHIEVED AS MONTH3_MILESTONE_ACHIEVED, ck3.MONTH_APPROVED_DATE AS MONTH3_APPROVED_DATE,
ck6.REASONCODE AS REASONCODE6,
CASE WHEN ck6.REASONCODE = 'OT6' THEN "Outcome at 6 month" END MONTH6_REASON,
ck6.MONTH_START_DATE AS MONTH6_START_DATE, ck6.MONTH_END_DATE AS MONTH6_END_DATE, ck6.MONTH_OUTCOME_EMP_SITUATION AS MONTH6_OUTCOME_EMP_SITUATION,
ck6.MONTH_EMPLOYMENT_TYPE AS MONTH6_EMPLOYMENT_TYPE, ck6.MONTH_NUM_JOBS AS ,MONTH6_NUM_JOBS, ck6.MONTH_NAICS_DESC AS MONTH6_NAICS_DESC, ck6.MONTH_JOB_NATURE AS MONTH6_JOB_NATURE,
ck6.MONTH_WORK_HOURS AS MONTH6_WORK_HOURS, ck6.MONTH_WAGE AS MONTH6_WAGE, ck6.MONTH_STUDENT_STATUS AS MONTH6_STUDENT_STATUS, ck6.MONTH_GOT_SERVICE AS MONTH6_GOT_SERVICE,
ck6.MONTH_RIGHT_SERVICE AS MONTH6_RIGHT_SERVICE, ck6.MONTH_RECOMMEND_PROGRAM AS MONTH6_RECOMMEND_PROGRAM, ck6.MONTH_RESUBMIT_MILESTONE AS MONTH6_RESUBMIT_MILESTONE,
ck6.MONTH_MILESTONE_ACHIEVED AS MONTH6_MILESTONE_ACHIEVED, ck6.MONTH_APPROVED_DATE AS MONTH6_APPROVED_DATE
FROM PROGRAM as pg
LEFT JOIN CASEINFO as ch ON pg.CASEID = ch.CASEID
LEFT JOIN OUTCOME as oc ON pg.CASEID = oc.CASEID
LEFT JOIN ( SELECT cp.CASEID, cp.REASONCODE, cp.MONTH_OUTCOME_EMP_SITUATION, cpi.* FROM CHECKPOINT cp LEFT JOIN CHECKPOINTINFO cpi ON cp.CASEREVIEWID = cpi.CASEREVIEWID WHERE cpi.REASONCODE = 'OT1')ck1 ON pg.CASEID = ck1.CASEID
LEFT JOIN ( SELECT cp.CASEID, cp.REASONCODE, cp.MONTH_OUTCOME_EMP_SITUATION, cpi.* FROM CHECKPOINT cp LEFT JOIN CHECKPOINTINFO cpi ON cp.CASEREVIEWID = cpi.CASEREVIEWID WHERE cpi.REASONCODE = 'OT3')ck3 ON pg.CASEID = ck3.CASEID
LEFT JOIN ( SELECT cp.CASEID, cp.REASONCODE, cp.MONTH_OUTCOME_EMP_SITUATION, cpi.* FROM CHECKPOINT cp LEFT JOIN CHECKPOINTINFO cpi ON cp.CASEREVIEWID = cpi.CASEREVIEWID WHERE cpi.REASONCODE = 'OT6')ck6 ON pg.CASEID = ck6.CASEID
If someone could please help me turn this wide table into a long table, it would be much appreciated.
thank you
You need to do unpivot for outcome and reason columns. But first you need an extra column for overall reason. This is the query:
with a as (
select 12345 as case_reference,
'Employed' as OUTCOME_EMP_SITUATION,
'Employed' as MONTH1_EMP_SITUATION,
'Outcome at 1 month' as MONTH1_REASON,
'Employed' as MONTH3_EMP_SITUATION,
'Outcome at 3 month' as MONTH3_REASON,
'Employed' as MONTH6_EMP_SITUATION,
'Outcome at 6 month' as MONTH6_REASON
from dual
)
select
case_reference,
outcome_emp_situation,
month_reason
from (
select a.*,
cast(null as varchar2(1000)) as reason
from a
) a
unpivot(
(Outcome_emp_situation, Month_Reason)
for mon in (
(OUTCOME_EMP_SITUATION, reason) as 0,
(MONTH1_EMP_SITUATION, MONTH1_REASON) as 1,
(MONTH3_EMP_SITUATION, MONTH3_REASON) as 3,
(MONTH6_EMP_SITUATION, MONTH6_REASON) as 6
)
)
order by mon asc
CASE_REFERENCE | OUTCOME_EMP_SITUATION | MONTH_REASON
-------------: | :-------------------- | :-----------------
12345 | Employed | null
12345 | Employed | Outcome at 1 month
12345 | Employed | Outcome at 3 month
12345 | Employed | Outcome at 6 month
db<>fiddle here
UPD: The explanation below.
The tuple just after unpivot keyword is the result column names, column after for keyword identifies column group which produced that values. Tuples inside in define the columns' groups: for each group that columns' values will be passed to the corresponding (by position) columns of the result tuple and new row will be generated with the value of for column defined after as keyword.
So if you need more columns to be transferred to each row, you need to add new columns to the result tuple (after unpivot) and to each column group inside in. If for some reason you have not enough columns to pass for some groups, you can wrap your source query with outer select and add dummy (or constantly valued) columns for that groups.
Note:
Datatypes of each tuples should be the same (or convertible according to default datatype precedence). I.e. each tuple's member on the same position should have the same type, members at different positions may have different types.
You can reuse the same column in multiple groups and positions.
Yes, I know this seems simple:
SELECT DISTINCT(...)
Except, it apparently isn't
Here is my actual Query:
SELECT
DeclinationReasons.Reason,
EmployeeInformation.ID,
EmployeeInformation.Employee,
EmployeeInformation.Active,
CompletedTrainings.DecShotDate,
CompletedTrainings.DecShotLocation,
CompletedTrainings.DecReason,
CompletedTrainings.DecExplanation,
IIf([DecShotLocation]="MCS","Yes","No") AS YesMCS,
IIf([DecReason]=1,1,0) AS YesAllergy,
IIf([DecReason]=2,1,0) AS YesImmune,
IIf([DecReason]=3,1,0) AS YesAdverse,
IIf([DecReason]=4,1,0) AS YesMedical,
IIf([DecReason]=5,1,0) AS YesSpiritual,
IIf([DecReason]=6,1,0) AS YesOther,
IIf([DecReason]=7,1,0) AS YesAlready
FROM
EmployeeInformation
INNER JOIN (CompletedTrainings
LEFT JOIN DeclinationReasons ON CompletedTrainings.DecReason = DeclinationReasons.ReasonID)
ON EmployeeInformation.ID = CompletedTrainings.Employee
GROUP BY
DeclinationReasons.Reason,
EmployeeInformation.ID,
EmployeeInformation.Employee,
EmployeeInformation.Active,
CompletedTrainings.DecShotDate,
CompletedTrainings.DecShotLocation,
CompletedTrainings.DecReason,
CompletedTrainings.DecExplanation,
IIf([DecShotLocation]="MCS","Yes","No"),
IIf([DecReason]=1,1,0),
IIf([DecReason]=2,1,0),
IIf([DecReason]=3,1,0),
IIf([DecReason]=4,1,0),
IIf([DecReason]=5,1,0),
IIf([DecReason]=6,1,0),
IIf([DecReason]=7,1,0)
HAVING
((((EmployeeInformation.Active) Like -1)
AND ((CompletedTrainings.DecShotDate + 365 >= DATE())
OR (CompletedTrainings.DecShotDate IS NULL))));
This is Joining a few tables (obviously) in order to get a number of records. The problem is that if someone is duplicated on the table with a NULL in one of the date fields, and a date in another field, it pulls both the NULL and the DATE, or pulls multiple NULLS it might pull multiple dates but those are not present right at the moment.
I need the Nulls, they are actual data in this particular case, but if someone has a date and a NULL I need to pull only the newest record, I thought I could add MAX(RecordID) from the table, but that didn't change the results of the query either.
That code:
SELECT
DeclinationReasons.Reason,
EmployeeInformation.ID,
EmployeeInformation.Employee,
EmployeeInformation.Active,
MAX(CompletedTrainings.RecordID),
CompletedTrainings.DecShotDate
...
And it returned the same issue, Duplicated EmployeeInformation.ID with different DecShotDate values.
Currently it returns:
ID
Active
DecShotDate
etc. x a bunch
1
-1
date date
whatever goes
2
-1
in these
2
-1
date date
columns
These are being used in a report, that is to determine the total number of employees who fit the criteria of the report. The NULLs in DecShotDate are needed as they show people who did not refuse to get a flu vaccine in the current year, while the dates are people who did refuse.
Now I have come up with one simple solution, I could add a column to the CompletedTrainings Table that contains a date or other value, and add that to the HAVING statement. This might be the right solution as this is a yearly training questionnaire that employees have to fill out. But I am asking for advice before doing this.
Am I right in thinking I need to add a column to filter by so that older data isn't being pulled, or should I be able to do this by pulling recordID, and did I just bork that part of the query up?
Edited to add raw table views:
EmployeeInformation Table:
ID
Last
First
empID
Active
Termdate
DoH
Title
PT/FT/PD
PI
1
Doe
Jane
982
-1
date
Sr
PD
X
2
Roe
John
278
0
date
date
Jr
PD
X
3
Moe
Larry
1232
-1
date
Sr
FT
X
4
Zoe
Debbie
1424
-1
date
Sr
PT
X
DeclinationReasons Table:
ReasonID
Reason
1
Allergy
2
Already got it
3
Illness
CompletedTrainings Table:
RecordID
Employee
Training
...
DecShotdate
DecShotLocation
DecShotReason
DecExp
1
1
4
date
location
2
text
2
1
4
3
2
4
4
3
4
date
location
3
text
5
3
4
date
location
1
text
6
4
4
After some serious soul searching, I decided to use another column and filter by that.
In the end my query looks like this:
SELECT *
FROM (
(
SELECT RecordID, DecShotDate, DecShotLocation, DecReason, DecExplanation, Employee,
IIf([DecShotLocation]="MCS","Yes","No") AS YesMCS, IIf([DecReason]=1,1,0) AS YesAllergy,
IIf([DecReason]=2,1,0) AS YesImmune, IIf([DecReason]=3,1,0) AS YesAdverse,
IIf([DecReason]=4,1,0) AS YesMedical, IIf([DecReason]=5,1,0) AS YesSpiritual,
IIf([DecReason]=6,1,0) AS YesOther, IIf([DecReason]=7,1,0) AS YesAlready
FROM CompletedTrainings WHERE (CompletedDate > DATE() - 365 ) AND (Training = 69)) AS T1
LEFT JOIN
(
SELECT ID, Active FROM EmployeeInformation) AS T2 ON T1.Employee = T2.ID)
LEFT JOIN
(
SELECT Reason, ReasonID FROM DeclinationReasons) AS T3 ON T1.DecReason = T3.ReasonID;
This may not have been the best solution, but it did exactly what I needed. Which is to get the information by latest entry into the database.
Previously I had tried to use MAX(), DISTINCT(), etc. but always had a problem of multiple records being retrieved. In this case, I intentionally SELECT the most recent records first, then join them to the results of the next query, and so on. Until I have all the required data for my report.
I write this in hopes someone else finds it useful. Or even better if someone tells me why this is wrong, so as to improve my own skills.
best explained with an example:
So I have users table:
id name product
1 second NULL
2 first 27
3 first 27
4 last 6
5 second NULL
And I would like to order them in this product order: [27,NULL, 6]
So I will get:
id name product
2 first 27
3 first 27
1 second NULL
5 second NULL
4 last 6
(notice user id 3 can be before user id 2 since they both have the same product value)
Now without NULL I could do it like that:
SELECT id FROM users ORDER BY users.product=27, users.product=6;
How can I do it with NULL ?
p.s.
I would like to do that for many records so it should be efficient.
You can use case to produce custom sort order:
select id
from users
order by case
when product = 27
then 1
when product is null
then 2
when product = 6
then 3
end
As a note, you can follow your original approach. You just need a NULL-safe comparison:
SELECT id
FROM users
ORDER BY (NOT users.product IS DISTINCT FROM 27)::int DESC,
(user.product IS NULL)::int DESC,
(NOT users.product IS DISTINCT FROM 6)::int DESC;
The reason your version has unexpected results is because the first comparison can return NULL, which is ordered separately from the "true" and "false".
I see that in an SQL query, the GROUP BY has to precede the ORDER BY expression. Does this imply that ordering is done after grouping would have discarded identical rows?
Because I seem to need to order rows by a timestamp first, then discard the rows with identical timestamp. And I don't know how to accomplish this.
I am using MySQL 5.1.41.
Here is the definition of the table expressed with create table:
create table
(
A int,
B timestamp
)
The data could be:
+-----+-----------------------+
| A | B |
+-----+-----------------------+
| 1 | today |
| 1 | yesterday |
| 2 | yesterday |
| 2 | tomorrow |
+-----+-----------------------+
The results of the query on the above table, which I am after, would be:
+-----+-----------------------+
| A | B |
+-----+-----------------------+
| 1 | today |
| 2 | tomorrow |
+-----+-----------------------+
Basically, I want the rows with the latest timestamp in column "B" (hence the mention of ORDER BY), and only one row for each value in column "A" (think DISTINCT or GROUP BY).
The actual problem behind the simplified example above:
In reality, I have two tables - users and payment_receipts:
create table users
(
phone_nr int(10) unsigned not null,
primary key (phone_nr)
)
create table payment_receipts
(
phone_nr int(10) unsigned not null,
payed_ts timestamp default current_timestamp not null,
payed_until_ts timestamp not null,
primary key (phone_nr, payed_ts, payed_until_ts)
)
The tables may include other columns but I omit these as irrelevant. Implementing a payment scheme, I have to send SMS to users across the cellular network, in periodic intervals depending on whether the payment is due or not. The payment is actualized when the SMS is sent as the recipient is taxed for it. I use the payment_receipts table to keep records of all payments done, i.e. for book-keeping. This is intended to model a real shop where both the buyer and the seller get a copy of the receipt of purchase, for reference. This table stores my (seller's) copy [of each receipt]. The customer's receipt is the received SMS itself. Each time an SMS is sent (and thus a payment is accomplished), the table is inserted a receipt record, stating who paid, when and "until when". To explain the latter, imagine a subscription service, but one which spans indefinitely until the user opt-out explicitly, at which point the corresponding user record is removed. A payment is made a month in advance, so as a rule, the difference between the payed_ts and payed_until_ts is 30 days worth of time.
I have a batch job that executes every day and needs to select a list of users that are due monthly payment as part of the automatic subscription renewal described above. To link this to the dummy example earlier, the phone number column phone_nr would be the column "A" and payed_until_ts would be column "B", but in reality there are two tables, which has to do with the following behaviour: when a user record is removed, the receipt must remain, for book-keeping. So not only do I need to group payments by date and discard all but the latest payment receipt date, I also need to watch out not to select receipts for which there no longer is a matching user record.
To solve the problem of selecting required records -- those that are due payment -- I need to find receipts with the latest payed_until_ts timestamp for each phone_nr (there may be several, obviously) and out of those records I further need to select only those phone numbers where payed_until_ts is earlier than the time the batch job executes. I then would send an SMS to each of these numbers, inserting a receipt record for each sent SMS, where payed_ts is now() and payed_until_ts is now() + interval 30 days.
But I can't seem to come up with the query required.
Select a,b from (select a,b from table order by b) as c group by a;
Yes, grouping is done first, and it affects a single select whereas ordering affects all the results from all select statements in a union, such as:
select a, 'max', max(b) from tbl group by a
union all select a, 'min', min(b) from tbl group by a
order by 1, 2
(using field numbers in order by since I couldn't be bothered to name my columns). Each group by affects only its select, the order by affects the combined result set.
It seems that what you're after can be achieved with:
select A, max(B) from tbl group by A
This uses the max aggregation function to basically do your pre-group ordering (it doesn't actually sort it in any decent DBMS, rather it will simply choose the maximum from an suitable index if available).
SELECT DISTINCT a,b
FROM tbl t
WHERE b = (SELECT MAX(b) FROM tbl WHERE tbl.a = t.a);
According to your new rules (tested with PostgreSQL)
Query You'd Want:
SELECT pr.phone_nr, pr.payed_ts, pr.payed_until_ts
FROM payment_receipts pr
JOIN users
ON (pr.phone_nr = users.phone_nr)
JOIN (select phone_nr, max(payed_until_ts) as payed_until_ts
from payment_receipts
group by phone_nr
) sub
ON ( pr.phone_nr = sub.phone_nr
AND pr.payed_until_ts = sub.payed_until_ts)
ORDER BY pr.phone_nr, pr.payed_ts, pr.payed_until_ts;
Original Answer (with updates):
CREATE TABLE foo (a NUMERIC, b TEXT, DATE);
INSERT INTO foo VALUES
(1,'a','2010-07-30'),
(1,'b','2010-07-30'),
(1,'c','2010-07-31'),
(1,'d','2010-07-31'),
(1,'a','2010-07-29'),
(1,'c','2010-07-29'),
(2,'a','2010-07-29'),
(2,'a','2010-08-01');
-- table contents
SELECT * FROM foo ORDER BY c,a,b;
a | b | c
---+---+------------
1 | a | 2010-07-29
1 | c | 2010-07-29
2 | a | 2010-07-29
1 | a | 2010-07-30
1 | b | 2010-07-30
1 | c | 2010-07-31
1 | d | 2010-07-31
2 | a | 2010-08-01
-- The following solutions both retrieve records based on the latest date
-- they both return the same result set, solution 1 is faster, solution 2
-- is easier to read
-- Solution 1:
SELECT foo.a, foo.b, foo.c
FROM foo
JOIN (select a, max(c) as c from foo group by a) bar
ON (foo.a=bar.a and foo.c=bar.c)
ORDER BY foo.a, foo.b, foo.c;
-- Solution 2:
SELECT a, b, MAX(c) AS c
FROM foo main
GROUP BY a, b
HAVING MAX(c) = (select max(c) from foo sub where main.a=sub.a group by a)
ORDER BY a, b;
a | b | c
---+---+------------
1 | c | 2010-07-31
1 | d | 2010-07-31
2 | a | 2010-08-01
(3 rows)
Comment:
1 is returned twice because their are multiple b values. This is acceptable (and advised). Your data should never have this problem, because c is based on b's value.
create table user_payments
(
phone_nr int NOT NULL,
payed_until_ts datetime NOT NULL
)
insert into user_payments
(phone_nr, payed_until_ts)
values
(1, '2016-01-28'), -- today
(1, '2016-01-27'), -- yesterday
(2, '2016-01-27'), -- yesterday
(2, '2016-01-29') -- tomorrow
select phone_nr, MAX(payed_until_ts) as latest_payment
from user_payments
group by phone_nr
-- OUTPUT:
-- phone_nr latest_payment
-- 1 2016-01-28 00:00:00.000
-- 2 2016-01-29 00:00:00.000
In the above example, I have used datetime column but similar query should work for timestamp column.
The MAX function will basically do the "ORDER BY" payed_until_ts column and pick the latest value for each phone_nr.
Also, you will get only one value for each phone_nr due to "GROUP BY" clause.