![]() ![]() DECODE is proprietary to Oracle.Ĩ) CASE executes faster in the Optimizer than does DECODE.ĩ) CASE is a statement while DECODE is a function. SELECT CASE WHEN NULL is NULL THEN 'This is Null'ħ) CASE complies with ANSI SQL. SELECT CASE NULL WHEN NULL THEN 'This is Null' ORA-00932: inconsistent datatypes: expected NUMBER got CHARĦ) CASE handles NULL differently : SELECT DECODE(NULL,NULL,'This is Null' exec proc_test(decode(:a,'THREE',3,0)) ĥ) CASE expects datatype consistency, DECODE does not. exec proc_test(case :a when 'THREE' then 3 else 0 end) Ībove statement will not give error but below statement gives error. ![]() If the ELSE is not coded, NULL is returned.ĬASE can even work as a parameter to a procedure call, while DECODE cannot. If none of the WHEN values match the given expression, the ELSE value is returned. The first TRUE expression cause oracle to return the corresponding THEN value. If the first result is NULL, then the return value is converted. The searched CASE allow multiple comparison expression (, =, BETWEEN, LIKE, IN, IS NULL, etc.). The DECODE function returns a value that is the same datatype as the first result in the list. If the ELSE is not coded, NULL is returned. ,defaultreturnvalue ) with: expression is the value to evaluate. Syntax: decode ( expression, comparevalue, returnvalue, ,compare, returnvalue. ![]() Its an alternative for the CASE statement which was introduced in Oracle 8. If none of the WHEN value match with given value/expression, the ELSE values is returned. The decode function can be used in SQL for and IF-THEN-ELSE construction. Simple case expression use for an equal condition on the given value or expression.The first WHEN value which is match with given value, return corresponding THEN value. A) Simple CASE statement: CASE expression WHEN this1 THEN that1 The CASE expression is a more flexible version of the DECODE function. Oracle support two flavors of CASE, simple and searched. The maximum number of components in the DECODE function, including expr, searches, results, and default, is 255.The CASE expression was first added to SQL in Oracle8i. Oracle9i extends its support to PL/SQL to allow CASE to be used as an expression or statement. 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 data type CHAR or if the first result is null, then Oracle converts the return value to the data type VARCHAR2. Oracle automatically converts the return value to the same data type as the first result. Oracle automatically converts expr and each search value to the data type of the first search value before comparing. Consequently, Oracle never evaluates a search if a previous search is equal to expr. 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 data type, and returns that data type. The string returned is of VARCHAR2 data type and is in the same character set as the first result parameter. expr, search, and result can be any of the data types 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 no match is found, then Oracle returns default. If expr is equal to a search, then Oracle Database returns the corresponding result. DECODE compares expr to each search value one by one. ![]()
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