mysql常用sql語句記錄1

1.解決返回值為null的問題

//假設name,addr返回的值中可能存在null值

select id,name,addr from tabe1 where id=1;
//修改的後的sql為
select id,
case when name is null 
then ''
else name 
end as name,
case when addr is null 
then ''
else addr 
end as addr
from tabe_name where id=
1;

//假設存在兩種表table1,table2

insert into table1 as t1 (id,name,addr) 
values (1,
'lisi'
,(select addr from table2 t2 where t2.id in
(select id from table 3 where id>1)
))

//對查詢結果中的id欄位全部+1,

select id+
1 as id,name,addr from tabe1;
//還可以進行字串拼接
select id,name,addr,name+addr as n from tabe1;

insert into table1 (age,num) 

select age+
1 as age,num+
2 as num from table2 where id=
3;

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