ORACLE VERSION : 19C
I am working on a legacy select query which returns around 60k rows. It İS formed of 9 joins and 2 unions. I want to exclude a small number of audience if they are inside the case i specified.
I wrote a select query using four joins and then used not in clause to exclude these audience.
The query was executing in aroung 15seconds before but after i wrote this not in clause it did not finish even in 20 minutes and i aborted it.
It is coded like this;
A.ID NOT IN (SELECT A.ID
FROM A
INNER JOIN B
ON A.X = BX
INNER JOIN C
ON B.Y = C.Y
INNER JOIN D
ON C.Z = D.Z)
However if i execute this subquery before the select and insert it into a table and then use not in clause for the table it almost finishes in 15 seconds just as normal
It is coded like this;
A.ID NOT IN (SELECT GT.ID FROM GENERATED_TABLE GT)
Do you know why it takes too much time when it is not populated into a table?
And are there any way to make the first one run faster?
Expecting it to take much less time
Try to use EXISTS instead of IN statement. The EXISTS clause is much faster than IN when the subquery results is very large.
And again - check EXPLAIN PLAN and search for FULL SCAN keywords. That will be the main cause.
SEL COUNT(*) FROM DATABASE_A.QF
Count = 37,011,480
SEL COUNT(*) FROM DATABASE_A_INC.QFA
Count = 368,454
Query 1
DELETE A
FROM
DATABASE_A.QF A,
DATABASE_A_INC.QFA B
WHERE
A.Q_NUM = B.Q_NUM
AND
A.ID = B.ID
AND
A.LOCATION_ID=1;
The above DELETE query runs into SPOOL space issue.
So I rewrote it in another form.
Query 2
DELETE FROM DATABASE_A.QF A WHERE (Q_NUM,ID) IN
(SELECT Q_NUM,ID FROM DATABASE_A_INC.QFA B)
AND LOCATION_ID=1;
368454 rows processed.
DELETE Command Complete
My questions:
Are query 1 and 2 logically the same? Are they deleting the same records?
How do I verify the count from Query 1 without running into a SPOOL
space issue? I have tried a general COUNT function. I tried increasing spool space to a certain extent.
Is there a better way to check the count for Query 1?
The queries are logically the same, yes. My guess is the reason for your SPOOL space issue is that you are listing your tables with commas instead of joining them. Try counting query 1 like this:
SELECT COUNT(*)
FROM DATABASE_A.QF A
INNER JOIN DATABASE_A_INC.QFA B ON A.Q_NUM = B.Q_NUM
WHERE A.ID = B.ID
AND A.LOCATION_ID=1;
I went through some PL/SQL codes and found a piece of query where I not actually get how it works. Hoping to get some technical advise from here.
The piece of query was shown as below:
SELECT a.ROWID
FROM TableA a
WHERE a.object_name IN ('HEADERS','LINES','DELIVERIES')
AND a.change_type IN ('A','C')
AND a.ROWID NOT IN (SELECT MAX (b.ROWID)
FROM TableA b
WHERE b.object_name = a.object_name
AND b.change_type = a.change_type
AND b.pk1 = a.pk1
AND b.object_identifier = a.object_identifier
);
From what I know, the inner query should run first (correct me if I am wrong) and then the inner query result will used for the outer query.
For the above query, how the inner query run as it needs data from the outer query (data from alias TableA a).
Hope to have some guidance on this as I am very fresh in PL/SQL development.
Thanks!
It is not PL/SQL, just classic SQL statement.
The purpose seams to be
retrieve all the lines which are not the "last version" (biggest rowid for a couple pk1 and object_identifier)
The "not in" part will retrieve the max rowid for a couple (pk1 and object_identifier) and then, the outer query will retrive all the lines which are not the max rowid
In term of execution process, you can take a look at the explain plan to see what oracle is going to do.
The inner query does not run first. Conceptually, you can think of it running like this:
Run the outer query,
For each row in the other query, run the inner query using specific values for the a.* columns
If the inner query for that row doesn't return anything, output the outer query row to the result set
When I run this SELECT statement, I receive 642 rows...
SELECT *
FROM _DevLoadIn a
JOIN ArticleCompanyList b ON b.Company = a.Name
When I run this UPDATE statement, only 630 rows are updated...
UPDATE b
SET b.BGCompanyId = a.RelatedId
FROM _DevLoadIn a
JOIN ArticleCompanyList b ON b.Company = a.Name
The JOIN is identical, so how can the number of effected rows be different? Both statements execute without error. I don't see how this could be possible. Can anyone provide any insight? Am I missing something about how an update/join works?
Best guess is that there are more matches in A for each value of B. So the select statement returns the joined duplicates of A - but the update only updates the row once.
In other words, the additional values in your select are representations of B (not A).
---- updated post question edit -----
Are you sure that your are updating the right value? Make sure that the proper table (A or B) is on the left hand side of the update statement. It appears you've edited your question and switched places of what was originally posted. The theory is still the same however.
If b.BGCompanyId is already equal to a.RelatedId, it will not show as updated.
You could verify this by modifying your original query like so:
SELECT *
FROM _DevLoadIn a
JOIN ArticleCompanyList b ON b.Company = a.Name
WHERE b.BGCompanyID != a.RelatedId
Okay, I know there are a few posts that discuss this, but my problem cannot be solved by a conditional where statement on a join (the common solution).
I have three join statements, and depending on the query parameters, I may need to run any combination of the three. My Join statement is quite expensive, so I want to only do the join when the query needs it, and I'm not prepared to write a 7 combination IF..ELSE.. statement to fulfill those combinations.
Here is what I've used for solutions thus far, but all of these have been less than ideal:
LEFT JOIN joinedTable jt
ON jt.someCol = someCol
WHERE jt.someCol = conditions
OR #neededJoin is null
(This is just too expensive, because I'm performing the join even when I don't need it, just not evaluating the join)
OUTER APPLY
(SELECT TOP(1) * FROM joinedTable jt
WHERE jt.someCol = someCol
AND #neededjoin is null)
(this is even more expensive than always left joining)
SELECT #sql = #sql + ' INNER JOIN joinedTable jt ' +
' ON jt.someCol = someCol ' +
' WHERE (conditions...) '
(this one is IDEAL, and how it is written now, but I'm trying to convert it away from dynamic SQL).
Any thoughts or help would be great!
EDIT:
If I take the dynamic SQL approach, I'm trying to figure out what would be most efficient with regards to structuring my query. Given that I have three optional conditions, and I need the results from all of them my current query does something like this:
IF condition one
SELECT from db
INNER JOIN condition one
UNION
IF condition two
SELECT from db
INNER JOIN condition two
UNION
IF condition three
SELECT from db
INNER JOIN condition three
My non-dynamic query does this task by performing left joins:
SELECT from db
LEFT JOIN condition one
LEFT JOIN condition two
LEFT JOIN condition three
WHERE condition one is true
OR condition two is true
OR condition three is true
Which makes more sense to do? since all of the code from the "SELECT from db" statement is the same? It appears that the union condition is more efficient, but my query is VERY long because of it....
Thanks!
LEFT JOIN
joinedTable jt ON jt.someCol = someCol AND jt.someCol = conditions AND #neededjoin ...
...
OR
LEFT JOIN
(
SELECT col1, someCol, col2 FROM joinedTable WHERE someCol = conditions AND #neededjoin ...
) jt ON jt.someCol = someCol
...
OR
;WITH jtCTE AS
(SELECT col1, someCol, col2 FROM joinedTable WHERE someCol = conditions AND #neededjoin ...)
SELECT
...
LEFT JOIN
jtCTE ON jtCTE.someCol = someCol
...
To be honest, there is no such construct as a conditional JOIN unless you use literals.
If it's in the SQL statement it's evaluated... so don't have it in the SQL statement by using dynamic SQL or IF ELSE
the dynamic sql solution is usually the best for these situations, but if you really need to get away from that a series of if statments in a stroed porc will do the job. It's a pain and you have to write much more code but it will be faster than trying to make joins conditional in the statement itself.
I would go for a simple and straightforward approach like this:
DECLARE #ret TABLE(...) ;
IF <coondition one> BEGIN ;
INSERT INTO #ret() SELECT ...
END ;
IF <coondition two> BEGIN ;
INSERT INTO #ret() SELECT ...
END ;
IF <coondition three> BEGIN ;
INSERT INTO #ret() SELECT ...
END ;
SELECT DISTINCT ... FROM #ret ;
Edit: I am suggesting a table variable, not a temporary table, so that the procedure will not recompile every time it runs. Generally speaking, three simpler inserts have a better chance of getting better execution plans than one big huge monster query combining all three.
However, we can not guess-timate performance. we must benchmark to determine it. Yet simpler code chunks are better for readability and maintainability.
Try this:
LEFT JOIN joinedTable jt
ON jt.someCol = someCol
AND jt.someCol = conditions
AND #neededJoin = 1 -- or whatever indicates join is needed
I think you'll find it is good performance and does what you need.
Update
If this doesn't give the performance I claimed, then perhaps that's because the last time I did this using joins to a table. The value I needed could come from one of 3 tables, based on 2 columns, so I built a 'join-map' table like so:
Col1 Col2 TableCode
1 2 A
1 4 A
1 3 B
1 5 B
2 2 C
2 5 C
1 11 C
Then,
SELECT
V.*,
LookedUpValue =
CASE M.TableCode
WHEN 'A' THEN A.Value
WHEN 'B' THEN B.Value
WHEN 'C' THEN C.Value
END
FROM
ValueMaster V
INNER JOIN JoinMap M ON V.Col1 = M.oOl1 AND V.Col2 = M.Col2
LEFT JOIN TableA A ON M.TableCode = 'A'
LEFT JOIN TableB B ON M.TableCode = 'B'
LEFT JOIN TableC C ON M.TableCode = 'C'
This gave me a huge performance improvement querying these tables (most of them dozens or hundreds of million-row tables).
This is why I'm asking if you actually get improved performance. Of course it's going to throw a join into the execution plan and assign it some cost, but overall it's going to do a lot less work than some plan that just indiscriminately joins all 3 tables and then Coalesce()s to find the right value.
If you find that compared to dynamic SQL it's only 5% more expensive to do the joins this way, but with the indiscriminate joins is 100% more expensive, it might be worth it to you to do this because of the correctness, clarity, and simplicity over dynamic SQL, all of which are probably more valuable than a small improvement (depending on what you're doing, of course).
Whether the cost scales with the number of rows is also another factor to consider. If even with a huge amount of data you only save 200ms of CPU on a query that isn't run dozens of times a second, it's a no-brainer to use it.
The reason I keep hammering on the fact that I think it's going to perform well is that even with a hash match, it wouldn't have any rows to probe with, or it wouldn't have any rows to create a hash of. The hash operation is going to stop a lot earlier compared to using the WHERE clause OR-style query of your initial post.
The dynamic SQL solution is best in most respects; you are trying to run different queries with different numbers of joins without rewriting the query to do different numbers of joins - and that doesn't work very well in terms of performance.
When I was doing this sort of stuff an æon or so ago (say the early 90s), the language I used was I4GL and the queries were built using its CONSTRUCT statement. This was used to generate part of a WHERE clause, so (based on the user input), the filter criteria it generated might look like:
a.column1 BETWEEN 1 AND 50 AND
b.column2 = 'ABCD' AND
c.column3 > 10
In those days, we didn't have the modern JOIN notations; I'm going to have to improvise a bit as we go. Typically there is a core table (or a set of core tables) that are always part of the query; there are also some tables that are optionally part of the query. In the example above, I assume that 'c' is the alias for the main table. The way the code worked would be:
Note that table 'a' was referenced in the query:
Add 'FullTableName AS a' to the FROM clause
Add a join condition 'AND a.join1 = c.join1' to the WHERE clause
Note that table 'b' was referenced...
Add bits to the FROM clause and WHERE clause.
Assemble the SELECT statement from the select-list (usually fixed), the FROM clause and the WHERE clause (occasionally with decorations such as GROUP BY, HAVING or ORDER BY too).
The same basic technique should be applied here - but the details are slightly different.
First of all, you don't have the string to analyze; you know from other circumstances which tables you need to add to your query. So, you still need to design things so that they can be assembled, but...
The SELECT clause with its select-list is probably fixed. It will identify the tables that must be present in the query because values are pulled from those tables.
The FROM clause will probably consist of a series of joins.
One part will be the core query:
FROM CoreTable1 AS C1
JOIN CoreTable2 AS C2
ON C1.JoinColumn = C2.JoinColumn
JOIN CoreTable3 AS M
ON M.PrimaryKey = C1.ForeignKey
Other tables can be added as necessary:
JOIN AuxilliaryTable1 AS A
ON M.ForeignKey1 = A.PrimaryKey
Or you can specify a full query:
JOIN (SELECT RelevantColumn1, RelevantColumn2
FROM AuxilliaryTable1
WHERE Column1 BETWEEN 1 AND 50) AS A
In the first case, you have to remember to add the WHERE criterion to the main WHERE clause, and trust the DBMS Optimizer to move the condition into the JOIN table as shown. A good optimizer will do that automatically; a poor one might not. Use query plans to help you determine how able your DBMS is.
Add the WHERE clause for any inter-table criteria not covered in the joining operations, and any filter criteria based on the core tables. Note that I'm thinking primarily in terms of extra criteria (AND operations) rather than alternative criteria (OR operations), but you can deal with OR too as long as you are careful to parenthesize the expressions sufficiently.
Occasionally, you may have to add a couple of JOIN conditions to connect a table to the core of the query - that is not dreadfully unusual.
Add any GROUP BY, HAVING or ORDER BY clauses (or limits, or any other decorations).
Note that you need a good understanding of the database schema and the join conditions. Basically, this is coding in your programming language the way you have to think about constructing the query. As long as you understand this and your schema, there aren't any insuperable problems.
Good luck...
Just because no one else mentioned this, here's something that you could use (not dynamic). If the syntax looks weird, it's because I tested it in Oracle.
Basically, you turn your joined tables into sub-selects that have a where clause that returns nothing if your condition does not match. If the condition does match, then the sub-select returns data for that table. The Case statement lets you pick which column is returned in the overall select.
with m as (select 1 Num, 'One' Txt from dual union select 2, 'Two' from dual union select 3, 'Three' from dual),
t1 as (select 1 Num from dual union select 11 from dual),
t2 as (select 2 Num from dual union select 22 from dual),
t3 as (select 3 Num from dual union select 33 from dual)
SELECT m.*
,CASE 1
WHEN 1 THEN
t1.Num
WHEN 2 THEN
t2.Num
WHEN 3 THEN
t3.Num
END SelectedNum
FROM m
LEFT JOIN (SELECT * FROM t1 WHERE 1 = 1) t1 ON m.Num = t1.Num
LEFT JOIN (SELECT * FROM t2 WHERE 1 = 2) t2 ON m.Num = t2.Num
LEFT JOIN (SELECT * FROM t3 WHERE 1 = 3) t3 ON m.Num = t3.Num