drop table if exists t1,t2,t3;
create table t1 (libname varchar(21) not null, city text, primary key (libname));
create table t2 (isbn varchar(21) not null, author text, title text, primary key (isbn));
create table t3 (isbn varchar(21) not null, libname varchar(21) not null, quantity int ,primary key (isbn,libname));
insert into t2 values ('001','Daffy','A duck''s life');
insert into t2 values ('002','Bugs','A rabbit\'s life');
insert into t2 values ('003','Cowboy','Life on the range');
insert into t2 values ('000','Anonymous','Wanna buy this book?');
insert into t2 values ('004','Best Seller','One Heckuva book');
insert into t2 values ('005','EveryoneBuys','This very book');
insert into t2 values ('006','San Fran','It is a san fran lifestyle');
insert into t2 values ('007','BerkAuthor','Cool.Berkley.the.book');
insert into t3 values('000','New York Public Libra','1');
insert into t3 values('001','New York Public Libra','2');
insert into t3 values('002','New York Public Libra','3');
insert into t3 values('003','New York Public Libra','4');
insert into t3 values('004','New York Public Libra','5');
insert into t3 values('005','New York Public Libra','6');
insert into t3 values('006','San Fransisco Public','5');
insert into t3 values('007','Berkeley Public1','3');
insert into t3 values('007','Berkeley Public2','3');
insert into t3 values('001','NYC Lib','8');
insert into t1 values ('New York Public Libra','New York');
insert into t1 values ('San Fransisco Public','San Fran');
insert into t1 values ('Berkeley Public1','Berkeley');
insert into t1 values ('Berkeley Public2','Berkeley');
insert into t1 values ('NYC Lib','New York');
select t2.isbn,city,t1.libname,count(t1.libname) as a from t3 left join t1 on t3.libname=t1.libname left join t2 on t3.isbn=t2.isbn group by city,t1.libname;
isbn	city	libname	a
007	Berkeley	Berkeley Public1	1
007	Berkeley	Berkeley Public2	1
000	New York	New York Public Libra	6
001	New York	NYC Lib	1
006	San Fran	San Fransisco Public	1
select t2.isbn,city,t1.libname,count(distinct t1.libname) as a from t3 left join t1 on t3.libname=t1.libname left join t2 on t3.isbn=t2.isbn group by city having count(distinct t1.libname) > 1;
isbn	city	libname	a
007	Berkeley	Berkeley Public1	2
000	New York	New York Public Libra	2
select t2.isbn,city,t1.libname,count(distinct t1.libname) as a from t3 left join t1 on t3.libname=t1.libname left join t2 on t3.isbn=t2.isbn group by city having count(distinct concat(t1.libname,'a')) > 1;
isbn	city	libname	a
007	Berkeley	Berkeley Public1	2
000	New York	New York Public Libra	2
select t2.isbn,city,@bar:=t1.libname,count(distinct t1.libname) as a
from t3 left join t1 on t3.libname=t1.libname left join t2
on t3.isbn=t2.isbn group by city having count(distinct
t1.libname) > 1;
isbn	city	@bar:=t1.libname	a
007	Berkeley	Berkeley Public1	2
000	New York	New York Public Libra	2
SELECT @bar;
@bar
Berkeley Public2
select t2.isbn,city,concat(@bar:=t1.libname),count(distinct t1.libname) as a
from t3 left join t1 on t3.libname=t1.libname left join t2
on t3.isbn=t2.isbn group by city having count(distinct
t1.libname) > 1;
isbn	city	concat(@bar:=t1.libname)	a
007	Berkeley	Berkeley Public1	2
000	New York	New York Public Libra	2
SELECT @bar;
@bar
Berkeley Public2
drop table t1, t2, t3;
create table t1 (f1 int);
insert into t1 values (1);
create table t2 (f1 int,f2 int);
select t1.f1,count(distinct t2.f2),count(distinct 1,NULL) from t1 left join t2 on t1.f1=t2.f1 group by t1.f1;
f1	count(distinct t2.f2)	count(distinct 1,NULL)
1	0	0
drop table t1,t2;
create table t1 (f int);
select count(distinct f) from t1;
count(distinct f)
0
drop table t1;
create table t1 (a char(3), b char(20), primary key (a, b));
insert into t1 values ('ABW', 'Dutch'), ('ABW', 'English');
select count(distinct a) from t1 group by b;
count(distinct a)
1
1
drop table t1;
create table t1 (f1 int, f2 int);
insert into t1 values (0,1),(1,2);
select count(distinct if(f1,3,f2)) from t1;
count(distinct if(f1,3,f2))
2
drop table t1;
