- use:
Replace empty values with other values
Returns the first non-empty value
- expression:
COALESCE is a function, (expression_1, expression_2, ..., expression_n) refers to each parameter expression in turn, stops when encountering a non-null value and returns the value. If all expressions are null values, a null value will eventually be returned. The use of COALESCE is that most expressions that contain a null value will eventually return a null value
- Instance
There is an industry code table, as follows, there are four levels of industry code yjbm, two-level code ejbm, three-level code sajbm, four-level code sijbm
How to judge which level an industry belongs to?
First of all, the level of this industry code belongs to a tree structure, for example:
A
A01
A011
A012
A013
A014
B
B0
B01
B011
B012
B013
The specific industry code query that returns the industry is as follows
select COALESCE(sijbm,sajbm,ejbm,yjbm) as hybm,* from ioc_market.m_dr_tz_hyzd where hymc ='采矿业'result:
