I have a 15-digit number that needs to be stored in an Oracle table either as a number or as a text.
Will I be able to select records from the table based on the field ("Positions 1 thru 11" + "Position 13")?
Example: If the data is 123456789012345, I need to select rows from the table to extract all rows that contain value "123456789013" in that field.
Can an index be created in Oracle to ensure the above query performs as good as a normal select query on the entire data field.
If you are storing the column in text then something like this should solve your problem. Use the first if you need to query separately otherwise if you want to query on first eleven and thirteenth use the last example.
create index ix_firsteleven on TABLE (substr(COL, 1, 11))
create index ix_thrirteenth on TABLE (substr(COL, 13, 1))
or
create index ix_concatstr on TABLE (substr(COL, 1, 11) || substr(col_name, 13, 1))
Related
On my table (point1) I am trying to get, that for each table of the grouped rows (point 2) I will have new row inserted (point 3) at the beginning of each table with the value in the column "Metadata1" equal to value form "Column2" for original row number 2 (starting counting from 0).
Link to excel file:
https://filebin.net/cnb4pia0vvkg937g
Its hard to know how much of your requirement is generic or specific, but
TransformFirst = Table.TransformColumns(#"PriorStepName",{{"Count", each
#table(
{"Column1","Column2","Metadata1"},
{{_{0}[Column1],_{0}[Column2],_{2}[Column2]}}
) & _
}}),
Together=Table.Combine(TransformFirst[Count])
in Together
modifies all the tables in column Count to include an extra row that is made up up Row0/Col1 Row0/Col2 and Row2/Col2
It then combines all those tables into one table
I'm trying to speed up the following
create table tab2 parallel 24 nologging compress for query high as
select /*+ parallel(24) index(a ix_1) index(b ix_2)*/
a.usr
,a.dtnum
,a.company
,count(distinct b.usr) as num
,count(distinct case when b.checked_1 = 1 then b.usr end) as num_che_1
,count(distinct case when b.checked_2 = 1 then b.usr end) as num_che_2
from tab a
join tab b on a.company = b.company
and b.dtnum between a.dtnum-1 and a.dtnum-0.0000000001
group by a.usr, a.dtnum, a.company;
by using indexes
create index ix_1 on tab(usr, dtnum, company);
create index ix_2 on tab(usr, company, dtnum, checked_1, checked_2);
but the execution plan tells me that it's going to be an index full scan for both indexes, and the calculations are very long (1 day is not enough).
About the data. Table tab has over 3 mln records. None of the single columns are unique. The unique values here are pairs of (usr, dtnum), where dtnum is a date with time written as a number in the format yyyy,mmddhh24miss. Columns checked_1, checked_2 have values from set (null, 0, 1, 2). Company holds an id for a company.
Each pair can only have one value checked_1, checked_2 and company as it is unique. Each user can be in multple pairs with different dtnum.
Edit
#Roberto Hernandez: I've attached the picture with the execution plan. As for parallel 24, in our company we are told to create tables with options 'parallel [num] nologging compress for query high'. I'm using 24 but I'm no expert in this field.
#Sayan Malakshinov: http://sqlfiddle.com/#!4/40b6b/2 Here I've simplified by giving data with checked_1 = checked_2, but in real life this may not be true.
#scaisEdge:
For
create index my_id1 on tab (company, dtnum);
create index my_id2 on tab (company, dtnum, usr);
I get
For table tab Your join condition is based on columns
company, datun
so you index should be primarly based on these columns
create index my_id1 on tab (company, datum);
The indexes you are using are useless because don't contain in left most position columsn use ij join /where condition
Eventually you can add user right most potition for avoid the needs of table access and let the db engine retrive alla the inf inside the index values
create index my_id1 on tab (company, datum, user, checked_1, checked_2);
Indexes (bitmap or otherwise) are not that useful for this execution. If you look at the execution plan, the optimizer thinks the group-by is going to reduce the output to 1 row. This results in serialization (PX SELECTOR) So I would question the quality of your statistics. What you may need is to create a column group on the three group-by columns, to improve the cardinality estimate of the group by.
I have a table with about 1.5 million rows and three columns. Column 'timestamp' is of type REAL and indexed. I am accessing the SQLite database via PHP PDO.
The following three selects run in less than a millisecond:
select timestamp from trades
select timestamp + 1 from trades
select max(timestamp) from trades
The following select needs almost half a second:
select max(timestamp) + 1 from trades
Why is that?
EDIT:
Lasse has asked for a "explain query plan", I have run this within a PHP PDO query since I have no direct SQLite3 command line tool access at the moment. I guess it does not matter, here is the result:
explain query plan select max(timestamp) + 1 from trades:
[selectid] => 0
[order] => 0
[from] => 0
[detail] => SCAN TABLE trades (~1000000 rows)
explain query plan select max(timestamp) from trades:
[selectid] => 0
[order] => 0
[from] => 0
[detail] => SEARCH TABLE trades USING COVERING INDEX tradesTimestampIdx (~1 rows)
The reason this query
select max(timestamp) + 1 from trades
takes so long is that the query engine must, for each record, compute the MAX value and then add one to it. Computing the MAX value involves doing a full table scan, and this must be repeated for each record because you are adding one to the value.
In the query
select timestamp + 1 from trades
you are doing a calculation for each record, but the engine only needs to scan the entire table once. And in this query
select max(timestamp) from trades
the engine does have to scan the entire table, however it also does so only once.
From the SQLite documentation:
Queries that contain a single MIN() or MAX() aggregate function whose argument is the left-most column of an index might be satisfied by doing a single index lookup rather than by scanning the entire table.
I emphasized might from the documentation, because it appears that a full table scan may be necessary for a query of the form SELECT MAX(x)+1 FROM table
if column x be not the left-most column of an index.
I am building stacked column flash chart on my query. I would like to split values in column for different locations. For argument sake I have 5 ids in location 41, 3 ids in location 21, 8 ids in location 1
select
'' link,
To_Char(ENQUIRED_DATE,'MON-YY') label,
count(decode(location_id,41,id,0)) "location1",
count(decode(location_id,21,id,0)) "location2",
count(decode(location_id,1,id,0)) "location3"
from "my_table"
where
some_conditions = 'Y';
as a result of this query Apex is creating stacked column with three separate parts( hurray!), however it instead of having values 5,3 and 8, it returns three regions 16,16,16. ( 16 = 5 +3+8).
So obviously Apex is going through all decode conditions and adding all values.
I am trying to achieve something described in this
article
Apex doesn't appear to be doing anything funky, you'd get the same result running that query through SQL*Plus. When you do:
count(decode(location_id,41,id,0)) "location1",
.. then the count gets incremented for every row - it doesn't matter which column you include, and the zero is just treated as any fixed value. I think you meant to use sum:
sum(decode(location_id,41,1,0)) "location1",
Here each row is assigned either zero or one, and summing those gives you the number that got one, which is the number that had the specified id value.
Personally I'd generally use caseover decode, but the result is the same:
sum(case when location_id = 41 then 1 else 0 end) "location1",
I have ColumnA in table. The data of each row is single character between A & H.
I want my select query to return 1 for 'A', 2 for B .... 8 for H.
My query always returns only one row. I can make a lookup table.
Anyone has better ideas to achieve the same ?
SELECT 1 + ASCII(columnA) - ASCII('A')
FROM table