![]() ![]() The maximum number of components in the DECODE function, including expr, searches, results, and default, is 255. If expr is null, then Oracle returns the result of the first search that is also null. In a DECODE function, Oracle considers two nulls to be equivalent. If the first result has the datatype CHAR or if the first result is null, then Oracle converts the return value to the datatype VARCHAR2. DECODE function is used to implement if-then-else logic in your SQL query without. Oracle automatically converts the return value to the same datatype as the first result. In this article, we will be learning about the DECODE function in Oracle. Oracle automatically converts expr and each search value to the datatype of the first search value before comparing. Consequently, Oracle never evaluates a search if a previous search is equal to expr. That is, the database evaluates each search value only before comparing it to expr, rather than evaluating all search values before comparing any of them with expr. Oracle Database uses short-circuit evaluation. The search, result, and default values can be derived from expressions. If the first search-result pair are numeric, then Oracle compares all search-result expressions and the first expr to determine the argument with the highest numeric precedence, implicitly converts the remaining arguments to that datatype, and returns that datatype. The string returned is of VARCHAR2 datatype and is in the same character set as the first result parameter. expr, search, and result can be any of the datatypes CHAR, VARCHAR2, NCHAR, or NVARCHAR2. If expr and search are character data, then Oracle compares them using nonpadded comparison semantics. The arguments can be any of the numeric types ( NUMBER, BINARY_FLOAT, or BINARY_DOUBLE) or character types. If default is omitted, then Oracle returns null. If you are running on Ubuntu, you will simply need to install package postgresql-9.1-orafce to make orafce available in your PostgreSQL server. Among other Oracle specific functions, orafce also implements DECODE - one that you are looking for. If expr is null, then Oracle returns the result of the first search that is also null. If you are used to Oracle specific functions, you might want to install PostgreSQL extension orafce. If no match is found, then Oracle returns default. In a DECODE function, Oracle considers two nulls to be equivalent. If expr is equal to a search, then Oracle Database returns the corresponding result. ![]() In order to use the sign function, we first need to map the "Low" range to negative numbers, the "Medium" range to 0, and the "High" range to positive numbers.Description of the illustration decode.gifĭECODE compares expr to each search value one by one. In the following example, the Oracle DECODE () function compares the first argument (1) with the second argument (1). while checking conditions first condition itself satisfied DECODE. As we have 3 ranges, we need 3 values, and there is a SQL function that returns exactly 3 possible values (and was already supported back then) - the sign function. DECODE statement works on ORACLE database only. If expression is equal to a search, then the corresponding result is returned by the Oracle Database. DECODE compares the expression to each search value one by one. What is DECODE function in SQL In Oracle, DECODE function allows us to add procedural if-then-else logic to the query. We just need to convert each range to some unique discrete value. Examples of DECODE function Let’s start one by one. One option is to write a PL/SQL function that gets X as the input and returns the rank as the output.īut could we have a pure SQL solution? DECODE doesn't look like a good fit, because it works with discrete values, not with ranges. With a (Searched) CASE Expression it’s as simple as this: This rank is determined by the value of X and two thresholds – LOW_TH and HIGH_TH. ![]() This reminded me of a trick I came up with many years ago, probably before 8i □Ī table T has a column X, and we need a query that one of the items it returns is a rank – either “Low”, “Medium” or “High”. As Tim wrote:ĬASE expressions were first released in Oracle 8i Prior to that if we wanted something similar to a CASE expression in our SQL, we had to use the DECODE function. ![]() One of these examples is DECODE and CASE Expressions. Because the first argument equals the second one, the function returns the third argument which is the string Equal. Let’s see the following example: In this example, the DECODE () function compares the first argument (one) with the second argument (also one). Tim Hall wrote this post yesterday (as part of Joel Kallman Day 2022) with some examples for “the old way” vs. The SQL DECODE () function allows you to add procedure if-then-else logic to queries. ![]()
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