Oracle: efficiently where clause to filter timestamp column to get all records of a specific day - sql

Question

I have a monthly partitioned table in Oracle by a timestamp column. This table contains > 1 billion rows from a 2019 history data. Now I want to filter this table to get all results for a specific day, regarding the HH24:MI:SS part.
The Problem (#1) I'm facing is that when using TO_CHAR(TIMESTAMPCOLUMN, 'YYYY-MM-DD'), the running time of my queries increases for more recent months. Example:
SELECT * FROM BIG_PART_TABLE WHERE TO_CHAR(TIMESTAMPCOLUMN, 'YYYY-MM-DD') = '2019-01-01' -- 3 sec
SELECT * FROM BIG_PART_TABLE WHERE TO_CHAR(TIMESTAMPCOLUMN, 'YYYY-MM-DD') = '2019-02-01' -- 6 sec
SELECT * FROM BIG_PART_TABLE WHERE TO_CHAR(TIMESTAMPCOLUMN, 'YYYY-MM-DD') = '2019-12-01' -- 36 sec
So I got rid of the TO_CHAR and started to filter like this:
SELECT * FROM BIG_PART_TABLE WHERE TIMESTAMPCOLUMN BETWEEN DATE '2019-01-01' AND DATE '2019-01-02' -- 0.032 sec
SELECT * FROM BIG_PART_TABLE WHERE TIMESTAMPCOLUMN BETWEEN DATE '2019-12-01' AND DATE '2019-12-02' -- 0.031 sec
The Problem (#2) is that I'm to lazy to write a BETWEEN clause, apart from the fact that it increases the chance of errors.
Finally, what I really want is a efficient single where clause to filter my table, like:
SELECT * FROM BIG_PART_TABLE WHERE TIMESTAMPCOLUMN = DATE '2019-01-01'
Thanks for all.

Answer 1

The correct approach is not to use date functions on the date column - using functions like this makes the query non SARGable, meaning that it cannot take advantage of an index on the date column.
There is no syntactical sugar that would make the expression shorter to write.
I would also suggest using half-open intervals instead of between:
WHERE
TIMESTAMPCOLUMN >= DATE '2019-01-01'
AND TIMESTAMPCOLUMN < DATE '2019-01-02'
BETWEEN is inclusive on both ends, so your expression implies that timestamps on 2019-01-02 00:00:00 would be filtered in, while this is most likely not what you want.

Answer 2

Use the partition_extension_clause syntax:
SELECT *
FROM BIG_PART_TABLE PARTITION FOR (DATE '2019-12-01')
WHERE TRUNC(TIMESTAMPCOLUMN) = DATE '2019-12-01' ;
This code is still a bit messy. But at least this syntax allows you to use the same date literal instead of having to create a brand new date expression. And although the code has duplication, the duplication is a bit self-documenting: the first expression is to use partition-pruning to find the nearest segment, the second expression is to get the exact rows.

Answer 3

In order to use the partitioning, Oracle has to recognize the partitioning key. If it is using the full timestamp, then you might have a problem.
There is a reasonable chance it is using trunc(TIMESTAMPCOLUMN) or trunc(TIMESTAMPCOLUMN, 'DD'). If so, then you can use that
WHERE TRUNC(TIMESTAMPCOLUMN) = DATE '2019-01-01'
Once you figure it out, you can add a computed column to the table, so you have:
alter table big_part_table add column timestampcolumn_date as trunc(timestampcolumn);
Then you can use timestampcolumn_date in the WHERE clause.

Answer 4

In the fastest way to in Orace access data is to use the partition-name.
Like in this example:
select * from BIG_PART_TABLE partition(ParititonName);