I'm building a calculated column that needs to sum all the rows in the same table that share a few common properties and have a greater date value.
I know I need to use calculate to break the filter context, but I'm not sure how to reference the row being calculated vs the table of the same name inside the calculate function. In Sql, this would be done as a self join with two different aliases for the same table, what is the DAX equivalent?
SQL pseudo code:
select
t1.Name
,sum(t2.a)
from table t1
inner join table t2 on t1.b = t2.b
and t1.c < t2.c
group by t1.name
DAX (how do I correctly reference outer row vs inner table?):
calculate(sum(table[a]),
filter(all(table), table[b] = table[b])
)
As suggested by #RADO, the earlier function does this (but you might not guess that from the name!).
Using my previous example, it looks like this:
calculate(sum(table[a]),
filter(all(table), table[b] = earlier(table[b]))
)
Related
I am trying to use FULLTEXT search as a preliminary filter before fetching data from another table. Consecutive JOINs follow to further refine the query and to mix-and-match rows (in reality there are up to 6 JOINs of the main table).
The first "filter" returns the IDs of the rows that are useful, so after joining I have a subset to continue with. My issue is performance, however, and my lack of understanding of how the SQL query is executed in SQLite.
SELECT *
FROM mytbl AS t1
JOIN
(SELECT someid
FROM myftstbl
WHERE
myftstbl MATCH 'MATCHME') AS prior
ON
t1.someid = prior.someid
AND t1.othercol = 'somevalue'
JOIN mytbl AS t2
ON
t2.someid = prior.someid
/* Or is this faster? t2.someid = t1.someid */
My thought process for the query above is that first, we retrieve the matched IDs from the myftstbl table and use those to JOIN on the main table t1 to get a sub-selection. Then we again JOIN a duplicate of the main table as t2. The part that I am unsure of is which approach would be faster: using the IDs from the matches, or from t2?
In other words: when I refer to t1.someid inside the second JOIN, does that contain only the someids after the first JOIN (so only those at the intersection of prior and those for which t1.othercol = 'somevalue) OR does it contain all the original someids of the whole original table?
You can assume that all columns are indexed. In fact, when I use one or the other approach, I find with EXPLAIN QUERY PLAN that different indices are being used for each query. So there must be a difference between the two.
The query should be simplified to
SELECT *
FROM mytbl AS t1
JOIN myftstbl USING (someid) -- or ON t1.someid = myftstbl.someid
JOIN mytbl AS t2 USING (someid) -- or ON t1.someid = t2.someid
WHERE myftstbl.{???} MATCH 'MATCHME' -- replace {???} with correct column name
AND t1.othercol = 'somevalue'
PS. The query logic is not clear for me, so it is saved as-is.
I want to compare a a value against 2 values without using OR or DECODE. The value I want to compare with two values is the one which I am getting as a return code of a function. If I use OR or DECODE then I have to call function twice and it gives performance hit. Currently I am coding as below
select *
from table1 t1, table2 t1
where t1.empid = t2.empid
and myfunction(t2.balance) = t1.total OR myfunction(t2.balance) = -1
Please suggest if there is a way to call function once and compare with 2 values.
To shorten your code you could use IN operator which acts like OR.
select *
from table1 t1
join table2 t1 on
t1.empid = t2.empid
and myfunction(t2.balance) in (t1.total, -1)
I've also replaced old-fashioned join syntax in where clause for JOIN keyword and you're advised to be using that in your future SQL journeys.
Good thing to know would be that even though you call the function twice, most modern databases would actually call it only once, so I wouldn't be that much concerned about it.
I'm getting this error no matter what I do with the INNER JOIN Statement
Here is my code:
SELECT Package_Code, Description, Duration, Site_Code
FROM tbl_Holiday_Details
INNER JOIN tbl_Site_Visted
ON tbl_Holiday_Details.Package_Code = tbl_Site_Visted.Package_Code
INNER JOIN tbl_Site_Visted
ON tbl_Site_Details.Site_Code = tbl_Site_Visted.Site_Code
I don't understand what is the problem.
ps. if needed i will provide more code
The immediate problem is that at least Package_Code and Site_Code exist in multiple tables but your select does not specify which table you want to return data from. Yes, you know that you're doing an inner join on those columns so it doesn't matter which table's value is returned but the SQL syntax doesn't allow Oracle to make that inference. Generally, I would advise that you always alias every column both so it is clear which table a particular attribute is coming from and so that you don't break code when you add an attribute to a different table that happens to have the same name.
SELECT tbl_Holiday_Details.Package_Code,
Description,
Duration,
tbl_Site_Visted.Site_Code
FROM tbl_Holiday_Details
INNER JOIN tbl_Site_Visted
ON tbl_Holiday_Details.Package_Code = tbl_Site_Visted.Package_Code
INNER JOIN tbl_Site_Visted
ON tbl_Site_Details.Site_Code = tbl_Site_Visted.Site_Code
will work assuming Description and Duration are defined only in one of the three tables. I would add aliases to Description and Duration as well but I don't know which of the tables should be used. Of course, I would generally use simpler aliases (say, tsv for tbl_Site_Visited) rather than the full table name.
If you want to avoid aliasing your columns, you could use the USING clause rather than the ON clause
SELECT Package_Code,
Description,
Duration,
Site_Code
FROM tbl_Holiday_Details
INNER JOIN tbl_Site_Visted
USING( Package_Code )
INNER JOIN tbl_Site_Visted
USING( Site_Code )
Think of my two tables have the same columns. One column is the ID, and the other one is the text. Is it possible to implement the following pseudo code in PLSQL?
Compare each row (They will have the same ID)
If anything is different about them
Run a couple of queries: an Update, and an Insert
ElseIf they are the same
Do nothing
Else the row does not exist
So add the row to the table compared on
Is it easy to do this using PLSQL or should I create a standalone application to do do this logic.
As your table have the same columns, by using NATURAL JOIN you can easily check if two corresponding rows are identical -- without need to update your code if a column is added to your table.
In addition, using OUTER JOIN allow you to find the rows present in one table but not in the other.
So, you can use something like that to achieve your purpose:
for rec in (
SELECT T.ID ID1,
U.ID ID2,
V.EQ
FROM T
FULL OUTER JOIN U ON T.ID = U.ID
FULL OUTER JOIN (SELECT ID, 1 EQ FROM T NATURAL JOIN U) V ON U.ID = V.ID)
loop
if rec.id1 is null
then
-- row in U but not in T
elsif rec.id2 is null
then
-- row in T but not in U
elsif rec.eq is null
-- row present in both tables
-- but content mismatch
end if
end loop
Else the row does not exist
So add the row to the table compared on
Is this condition means that rows can be missed in both tables? If only in one, then:
insert into t1 (id, text)
select id, text
from t2
minus
select id, text
from t1;
If missed records can be in both tables, you need the same query that inserts into table t2 rows from t1.
If anything is different about them
If you need one action for any amount of different rows, then use something like this:
select count(*)
into a
from t1, t2
where t1.id = t2.id and t1.text <> t2.text;
if a > 0 then
...
otherwise:
for i in (
select *
from t1, t2
where t1.id = t2.id and t1.text <> t2.text) loop
<do something>
end loop;
A 'merge' statement is what u needed.
Here is the syntax:
MERGE INTO TARGET_TABLE
USING SOURCE_TABLE
ON (CONDITION)
WHEN MATCHED THEN
UPDATE SET (DO YOUR UPDATES)
WHEN NOT MATCHED THEN
(INSERT YOUR NEW ROWS)
Google MERGE syntax for more about the statement.
Just use MINUS.
query_1
MINUS
query_2
In your case, if you really want to use PL/SQL, then select count into a local variable. Write a logic, if count > 0 then do other stuff.
I'm having a small issue with sorting the data returned from a query, with the aim of getting the oldest updated value in dataset so that I can update only that record. Here's what I'm doing:
WHERE ROWNUM = 1 AND TABLE1.ID != V_IGNOREID
AND TABLE1.LASTREADTIME = (SELECT MIN(TABLE1.LASTREADTIME) FROM TABLE1)
ORDER BY TABLE1.LASTREADTIME DESC;
It makes no difference as to whether the ORDER BY statement is included or not. If I only use the ROWNUM and equality checks, I get data, but it alternates between only two rows, which is why I'm trying to use the LASTREADTIME data (so that I can modify more than these two rows). Anybody have any thoughts on this, or any suggestions as to how I can use the MIN function effectively?
Cheers
select * from (
-- your original select without rownum and with order by
)
WHERE ROWNUM = 1
EDIT some explanation
I think the order by clause is applied on the resultset after the where clause. So if the rownum = 1 is in the same select statement with the order by, then it will be applied first and the order by will order only 1 row, which will be the first row of the unordered resultset.