If none of the conditions are satisfied, we can use an optional ELSE statement to return the default value. Once a condition evaluates successfully, it stops the evaluation of remaining conditions. SQL Server evaluates the conditions sequentially.
Therefore, in the earlier example, the CASE statements work as shown below.Īt a high-level, the syntax for a SQL CASE statement is shown below. In the below image, we see both the database and application perspective.Ī CASE statement in SQL Server evaluates an expression and returns a value based on the defined conditions. Customers just need to view whether the product is available or not. But, from the application perspective, the end-user does not require these values. It is beneficial for the SQL Server query optimizer in preparing the optimized execution plan. If we look at the database perspective, it is a good practice to use the abbreviations or bits wherever possible. Let’s say you store the values for a product’s availability as 1 or 0. Many times, we store the column values in bits 1 or 0. If a voter’s age is greater than 18, they are eligible to vote. If you were looking for logic about voting eligibility, this would be dependent upon the values in the DOB column. For example, suppose you have a voters table with the following details: If you want to learn more about the difference between rank, dense_rank and row_number, watch this video.A SQL CASE statement evaluates and returns results based on particular values, predicates and conditions as per defined logic. To do this and get the same rows every time, ensure there are no duplicated values in your order by columns. In all these examples you'll get at least three rows in your output. If you want all the rows for the first three values, use dense_rank in the subquery instead: select * from (ĭense_rank() over ( order by price desc ) rn
You can get the same effect using a subquery by swapping row_number for rank: select * from ( So you get both the 9.99 priced toys: select toy_name, price from toys
#Apex sql query results order plus#
This will return you N rows, plus any that have the same value for the order by columns as the last. You can guarantee you get both using fetch first. So if you fetch the three most expensive toys, you could get either of them! When doing a top-N query sorting by non-unique values, you have an important question to answer:ĭo you want exactly N rows, all the rows for the first N values, or N rows along with any that have the same value as the Nth?įor example, both Miss Snuggles and Blue Dinosaur have a price of 9.99. This goes after the order by and removes the need to use a subquery: select * from toys Oracle Database 12c introduced the ANSI compliant fetch first clause. Select t.*, row_number() over (order by price desc) rn
To use this in a top-N query, you must also use a subquery: select * from ( This is determined by the sort defined in the order by in the over clause. Like rownum, it assigns an incrementing counter. Then filter the results of this: select * from ( To fix this, sort the data in a subquery. For example, the following tries to get the three most expensive toys: select * from toysīut it includes the cheapest, Baby Turtle! This is because the database processes order by after where. It assigns an increasing number to each row you fetch.īut if you use it in a where clause before the order by, you'll get unexpected results. There are several way to do this in Oracle Database Rownum For example, to find the three cheapest toys.
#Apex sql query results order code#
And your code more resilient to changes!Ī top-N query returns the first N rows in a sorted data set. Then refer to this alias in the order by clause: select t.*, It's better to give the function an alias. And if you need to change the columns you're selecting, it's easy to overlook the positional order by.
Particularly if the query uses "select *". the case expression then toy_name: select t.*,īut this makes it hard to spot which column you're sorting by. So the following sorts by the sixth column then the first. This is where you put the number of the column in the select you want to order by (working from left to right in the output). You can avoid this by using positional notation or aliases. To help with this, include the expression in your select: select t.*,īut this means you have the function in two places! This makes code maintenance harder. It can be tricky to debug custom sorting functions.