What is the difference between decode and case when?

What is the difference between decode and case when?
Decode can only be equivalent, case when can be used for range, range can be used for condition differentiation, decode can do, and case when can also do; in terms of efficiency, I personally think the efficiency of the two is almost the same; however, the decode syntax is simpler, but it can only be used for equivalent comparison. case when end can be used to determine conditions.

 

CASE When in Oracle:

SELECT LogID, UserID, LogTime, Url, Description ,(
Case
When OperateType = 0 then 'add'
When OperateType = 1 then 'modify'
Else 'delete'
End) OperationName
FROM LOG

Decode () in Oracle ():
· Meaning:
Decode (condition, value 1, translation value 1, value 2, translation value 2,... value n, translation value n, default value)

SELECT LogID, UserID, LogTime, Url, Description,
Decode (OperateType, 0, 'add', 1, 'modify', 'delete') OperationName
FROM LOG

Difference: the two are similar in fixed comparison conditions, such as OperateType and fixed values 0, 1, and 2. However, when the comparison conditions are not fixed, for example, OperateType is changed to Sarlary, when the range is 0-,-or above, it is obviously easier to use case when.

 

 

In fact, decode and case when can often be equivalent. The choice of decode can be determined by the programmer's habits and proficiency. However, it is worth noting that the two forms of CaseWhen are listed as follows. I think the best analysis method is to write an SQL to test it. I will not talk about it here.

 

CASE ExprWHEN Comparison_expr1THEN Return_expr1[WHEN Comparison_expr2THEN Return_expr2WHEN Comparison_exprnTHEN Return_exprnELSE Else_expr] END (a variant of case when) CASEWHEN Comparison_expr1THEN Return_expr1[WHEN Comparison_expr2THEN Return_expr2WHEN Comparison_exprnTHEN Return_exprnELSE Else_expr] End decode ( Col | expression, search1, result1[ , Search2, result2 ,...,] [ , Searchn, resultn ,...,] [ , Default])

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