sqlite3 PM_617794.db
DROP TABLE IF EXISTS pdbs;
CREATE TABLE pdbs(
  PdbId       TEXT,
  MetalAtm    TEXT,
  MetalName   TEXT,
  MetalNumber INTEGER,
  MetalChn    TEXT,
  AtmName     TEXT,
  ResName     TEXT,
  ResNumber   INTEGER,
  ResChn      TEXT,
  Distance    NUMERIC
);
INSERT INTO pdbs VALUES('1nc7','MG','MG',1501,'-','CL','CL',1401,'-',3.065);
INSERT INTO pdbs VALUES('1nc7','MG','MG',1501,'-','CL','CL',1402,'-',2.660);
INSERT INTO pdbs VALUES('1pex','CA','CA', 503,'-','CL','CL', 501,'-',2.895);
INSERT INTO pdbs VALUES('1qhu','NA','NA',   3,'-','CL','CL',   1,'-',3.096);
INSERT INTO pdbs VALUES('1qjs','NA','NA', 513,'A','CL','CL', 511,'A',3.096);
INSERT INTO pdbs VALUES('1rtg','CA','CA',   2,'-','CL','CL',   1,'-',3.079);
INSERT INTO pdbs VALUES('1xj6','NA','NA',5002,'-','CL','CL',5001,'-',2.628);
INSERT INTO pdbs VALUES('2caj','NI','NI',1151,'B','CL','CL',1150,'B',3.551);
INSERT INTO pdbs VALUES('2oa9','CD','CD', 911,'-','CL','CL', 800,'-',2.291);
INSERT INTO pdbs VALUES('2oa9','CD','CD', 913,'-','CL','CL', 801,'-',2.403);
.mode column pdbs
.width 4 2 2 4 1 2 2 4 1 5

##</code><code>##

SELECT   *, COUNT(PdbId) as c
FROM     pdbs
GROUP BY PdbId
HAVING   c >= 2
;

##</code><code>##

1nc7  MG  MG  1501  -  CL  CL  1402  -  2.66   2
2oa9  CD  CD  913   -  CL  CL  801   -  2.403  2

##</code><code>##

SELECT     pdbs.*
FROM       pdbs JOIN (
  SELECT   PdbId, ResName, COUNT(*) as c
  FROM     pdbs
  GROUP BY PdbId, ResName
  HAVING   c >= 2
) AS       counter
ON         pdbs.PdbId   = counter.PdbId
AND        pdbs.ResName = counter.ResName
WHERE      pdbs.ResName = 'CL'
;

##</code><code>##

1nc7  MG  MG  1501  -  CL  CL  1401  -  3.065
1nc7  MG  MG  1501  -  CL  CL  1402  -  2.66
2oa9  CD  CD  911   -  CL  CL  800   -  2.291
2oa9  CD  CD  913   -  CL  CL  801   -  2.403