select *, count(distinct phonenumber) from quchong group by id,對電話號碼去重,回傳id和phonenumber以及其它列。用上面那條陳述句確實能回傳結果,但執行效率太慢,求解決辦法。id phonenumber以及其他列都添加了索引
uj5u.com熱心網友回復:
相同的電話號碼,id相同么?
如果相同電話號碼,id都相同,那么執行:
select distinct(id) from quchong
的效率高么?
uj5u.com熱心網友回復:
id不相同
uj5u.com熱心網友回復:
id 不相同, 以 id group 得到的結果有何意義?
直接回傳有多少號碼就得了:
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
相同的電話號碼,id相同么?
如果相同電話號碼,id都相同,那么執行:
select distinct(id) from quchong
的效率高么?
id不相同
id 不相同, 以 id group 得到的結果有何意義?
直接回傳有多少號碼就得了:
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
drop table if exists quchong;
create table quchong(
id int,
`phonenumber` varchar(20)
);
insert into quchong values(1,'13912345670');
insert into quchong values(2,'13912345671');
insert into quchong values(3,'13912345671');
insert into quchong values(4,'13912345671');
insert into quchong values(5,'13912345676');
insert into quchong values(6,'13912345676');
insert into quchong values(7,'13912345676');
insert into quchong values(8,'13912345678');
insert into quchong values(9,'13912345678');
insert into quchong values(10,'13912345679');
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