DB2函数

CAST(强制类型转换函数)

CAST是DB2中强制类型转换函数
CAST ( expression AS data_type )
若expression 为null或’'转换时会报错

select 
cast('N' as char(1)) char_str, 
cast(age as varchar(32)) age_char, age, 
cast(priority as int ) priority_int, priority 
from T_HELLO;

CASE

CASE 某个字段 WHEN 某个值 THEN 赋予某个值 ELSE 赋予另外个值 END

select 
case when name ='历史' then '666' when name='化学' then '999' else '0' end name_case, 
name 
from T_HELLO;

coalesce

COALESCE 函数功能 ：返回列表中的第一个非空表达式（如果所有参数均为 NULL，则 返回 NULL）；与Oracle数据库的nvl函数功能相同。
语法
COALESCE ( expression, expression [ , …] )

select coalesce(name, '666') name_coalesce, name from  T_HELLO;

select 
coalesce((select b.name from t_hello b where a.name=b.name), '666') name_coalesce, 
	name 
from  T_HELLO a;