Oracle slot count
I've notice that in Oracle, the query SELECT COUNT(*) FROM sometable; is very slow for large tables. It seems like the database it actually going through every row and incrementing a counter one. If the intention is only to count the number of Records matching the criteria then you could as well use: count(1).. This is the fastest as the numberical literal is the fastest to be summed up. Max rownum will lead to implicit ordering while count(id) will also be effecient as the value is a. Oct 27, · IF in Oracle function COUNT. Hi, I am writing a SQL query in Oracle and I have a column with COUNT function. Now I want to have IF statement in Oracle Reviews: 2.
IF in Oracle function COUNT
The Sampled of Executions column shows how many distinct executions of a particular SQL statement were sampled. Activity Over Time The Activity Over Time section of the ASH report is particularly useful for longer time periods because it provides in-depth details about activities and workload profiles during the analysis period. Semantic Nulls January 08, - 3: Careful examination revealed a subtle difference: Sign up using Email and Password.
Select Count(1): How it works
You have to decrease the number of row your query has to process. An index may help Oracle to count efficiently the number of rowa you are interested in. Since the plan shows it is using full table scan you can add indexes in the column used in where clause. You should change the name to correspond to your naming convention and make sure that it is unique.
Join them; it only takes a minute: Here's how it works: Anybody can ask a question Anybody can answer The best answers are voted up and rise to the top. Count is slow Oracle. This is the execution plan: Can anyone help me? Adeel ASIF 1 4. Is there any indexes created on the columns used in where clause?
This means it reads the table from begin to the end and reads all 16 millions of rows of the table table scan rows gotten This is a good value. So make an index on this column. You should add the columns from the other where -clauses and the select -clause to the index, too.
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Join Stack Overflow to learn, share knowledge, and build your career. It seems like the database it actually going through every row and incrementing a counter one at a time. I would think that there would be a counter somewhere in the table how many rows that table has.
So if I want to check the number of rows in a table in Oracle, what is the fastest way to do that? It would be impractical to have a different counter for each and every session so you have literally to count the rows. There are ways to speed up things however: Otherwise it is executes a full table scan. Have an index on a non-null column present that can be used for the scan.
Or create a function-based index as:. The fastest way to get a count of a table is exactly what you did. There are no tricks you can do that Oracle doesn't already know about. I'll admit I wouldn't be happy with 41 seconds but really WHY do you think it should be faster?
If you tell us the table has 18 billion rows and is running on the laptop you bought from a garage sale in , 41 seconds is probably not that far outside "good as it will get" unless you get better hardware. However if you say you are on Oracle 9 and you ran statistics last summer well you'll probably get a different suggestions.
Slotted antenna arrays used with waveguides are a popular antenna in navigation, radar and other high-frequency systems. They are simple to fabricate, have low-loss high antenna efficiency and radiate linear polarization with low cross-polarization. These antennas are often used in aircraft applications because they can be made to conform to the surface on which they are mounted. The slots are typically thin less than 0. The slots on the waveguide will assumed to have a narrow width.
Increasing the width increases the Bandwidth recall that a fatter antenna often has an increased bandwidth ; the expense of a larger width is a higher degree of cross-polarization. An example of a slotted waveguide array is shown in Figure 1 dimensions given by length a and width b Figure 1.
Basic geometry of a slotted waveguide antenna. As in the cavity-backed slot antenna , each slot could be independently fed with a voltage source across the slot. However, especially for large arrays this would be very difficult to construct, and I've never seen this done in practice. Instead, the waveguide is used as the transmission line to feed the elements. The position, shape and orientation of the slots will determine how or if they radiate.
In addition, the shape of the waveguide and frequency of operation will play a major role. To understand what is going on, we'll need to understand the fields within the waveguide first. For a primer on waveguides, see here: The dominant TE10 mode will be assumed to exist within the waveguide. Using the geometry of Figure 1, the fields that exist within the waveguide are given by: In the above, f is the frequency of interest, k is the wavenumber and is a constant that specifies how much power is added to the waveguide.
Magnetic fields tangent to a conductor produce electric currents on the surface. On the top wall of the waveguide where the slots are , the induced currents will be: Radiation occurs when the currents must "go around" the slots in order to continue on their desired direction.