group query result in which flag not included - mysql

Question

I have a table like this
NAME FLAG
---------------------------
abc 1
abc 0
abc 2
def 1
def 2
xyz 0
xyz 0
xyz 1
efg 1
I need query that list the name (group the result) which flag not included 0 and included 1.The result simply like below:-
NAME FLAG
------------------
def 1
efg 1
I have tried the query but not results the same.
select * mytable where FLAG NOT IN (0) GROUP BY NAME;

Answer 1

This is the simplest solution I can come up with. I believe there are more elegant answers possible.
SELECT *
FROM mytable
WHERE name NOT IN (SELECT name FROM mytable WHERE flag = 0)
AND flag = 1;

Answer 2

You can use NOT EXISTS clause in this way.
select a.*
from tbl a
where not exists
(select *
from tbl b
where b.name=a.name
and b.flag=0)
and a.flag=1;

Answer 3

We can use aggregation. The trick is to run a condition on each row, and then use an aggregate function to pick out the net result of the condition from all of the rows...
SELECT t.name
FROM a_table_like_this t
GROUP BY t.name
HAVING MAX(t.flag=0) <> 1
AND MAX(t.flag=1) = 1
The expressions in the HAVING clause are MySQL shorthand.
A more ANSI standards compliant equivalent would be:
SELECT t.name
FROM a_table_like_this t
GROUP BY t.name
HAVING MAX( CASE WHEN t.flag=0 THEN 1 ELSE 0 END) <> 1
AND MAX( CASE WHEN t.flag=1 THEN 1 ELSE 0 END) = 1
To get a better handle on what this is doing, take a look at how those expressions are evaluated on each row. Remove the GROUP BY clause, and move those expressions into the SELECT list...
SELECT t.name
, t.flag
, CASE WHEN t.flag=0 THEN 1 ELSE 0 END AS `fl=0`
, CASE WHEN t.flag=1 THEN 1 ELSE 0 END AS `fl=1`
FROM a_table_like_this t
ORDER
BY t.name
, t.flag
We get something like
name flag fl=0 fl=1
------ ---- ---- ----
abc 1 0 1
abc 0 1 0
abc 2 0 0
def 1 0 1
def 2 0 0
xyz 0 1 0
xyz 0 1 0
xyz 1 0 1
efg 1 0 1
If we now aggregate these rows by name (GROUP BY name), we can use MAX() aggregate to pick out a 1 (if there's one in the group. Otherwise, we'll get back a 0.)
And we can do conditional tests on the results of aggregates functions in the HAVING clause.