Postgres 9.6

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create table test (
id serial,  
testvar varchar(512)
);

insert into test (testvar) values('panathinaikos, olympiakos, aek ');
insert into test (testvar) values('olympiakos, aek ');
insert into test (testvar) values('aek, aris ');
1 rows affected

1 rows affected

1 rows affected

select * from test;


id
testvar


1
panathinaikos, olympiakos, aek

2
olympiakos, aek

3
aek, aris


SELECT id,array_to_string(regexp_matches(testvar,'^([^,]+),','i'), ';') AS result from test;


id
result


1
panathinaikos

2
olympiakos

3
aek


update test set testvar = t.result from (SELECT id,array_to_string(regexp_matches(testvar,'^([^,]+),','i'), ';') AS result from test) as t
where test.id = t.id;
3 rows affected

select * from test;


id
testvar


1
panathinaikos

2
olympiakos

3
aek