Oracle SQL query exercise skills (this is very practical, not blow)

 

Table data;

Menu_id	Is_tree
0001	1
0002	1
0101	2
0102
0103
0201	5
0202	6

 

 

 

 
-------------- Use the decode function select B. menu_id, decode (B. is_tree, '1', '1vv ', '2', '2vv', null, 'isullvalue', 'defaultvaluehe ') tree from menutree B -------------- use case when then else to achieve the same effect select C. menu_id, casewhen C. is_tree is null then 'isnullvalue' when C. is_tree = '1' then' 1vv 'when C. is_tree = '2' then' 2vv 'else' ultultvaluehe' end tree from menutree C
 

 

The above two SQL statements have the same effect.

 

 

 

Menu_id	Tree
0001	1vv
0002	1vv
0101	2vv
0102	Isnullvalue
0103	Isnullvalue
0201	Defaultvaluehehe
0202	Defaultvaluehehe