How to use when statement in oracle

In Oracle, the when statement is often used in conjunction with case to determine the situation of multiple fields. The syntax is "case column name when condition value 1 then option 1 when condition value 2 then option 2... else default value end".

The operating environment of this tutorial: Windows 10 system, Oracle version 12c, Dell G3 computer.

when statement in oracle

oracle case when usage

Case has two formats. Simple Case function and Case search function.

Usage of Case when in Oracle:

(a) Starts with case and ends with end;

(b) When is followed by condition, then displays the result ;

(c) else is the default case, similar to the default of switch case in high-level language programs, which can be omitted;

(d) end is followed by an alias;

Case has two kinds of expressions:

(A) Simple case expressions use expressions to determine the return value;

(B) Search case expressions and use conditions to determine the return value Value;

Example:

       select (case t.sex when '1' then '男' when '0' then '女' else t.sex end from emp t;
       select (case when t.sex ='1' then '男' when t.sex= '0' then '女'else t.sex end from emp t;

We use case when to convert the sex of 1 into male, the sex of 0 into female, and the others None of them are converted. Now let's change the code a little and see the effect.

In this way, when the gender code is 1 or 0, it is converted into male or female. If it is not 1 or 0, it is displayed as an error code.

Recommended tutorial: "Oracle Video Tutorial"

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