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CREATE TABLE Nums(
    a INT UNSIGNED NOT NULL PRIMARY KRY
    )ENGINE=InnoDB;

CREATE PRODURE CreateNums (t INT UNSIGNED )
BEGIN
DECLARE s INT UNSIGNED DEFAULT 1;
TRUNCATE TABLE Nums;
INSERT INTO Nums SELECT s;
WHILE s*2 <= t DO                       
BEGIN
INSERT INTO Nums SELECT a+s FROM Nums;
SET s = s*2
END;
END WHILE;
END;

CREATE TABLE t (a INT UNSIGNED NOT NULL PRIMARY KEY);
INSERT INTO t VALUES(1);
INSERT INTO t VALUES(2);
INSERT INTO t VALUES(3);
INSERT INTO t VALUES(100);
INSERT INTO t VALUES(101);
INSERT INTO t VALUES(103);
INSERT INTO t VALUES(104);
INSERT INTO t VALUES(105);

SELECT MIN(a) start,MAX(a) end FROM (
   SELECT a,rn,a-rn AS diff
   FROM (SELECT a,@a:=@a+1 rn FROM t,(SELECT @a:=0) AS a)
   AS b
)AS c
GROUP BY diff;

SELECT 
CASE 
WHEN NOT EXISTS (SELECT a FROM x WHERE a=1)THEN 1 
ELSE 
(SELECT MIN(a)+1 AS missing 
FROM x AS A 
WHERE NOT EXISTS 
(SELECT * FROM x AS B 
WHERE A.a+1=B.a))
END AS missing;

INSERT INTO x 
SELECT 
CASE 
WHEN NOT EXISTS (SELECT a FROM x WHERE a=1)THEN 1 
ELSE 
(SELECT MIN(a)+1 AS missing 
FROM x AS A 
WHERE NOT EXISTS 
(SELECT * FROM x AS B 
WHERE A.a+1=B.a)) END AS missing, 'p';

CREATE TABLE sales (
  empid varchar(10) NOT NULL,
  mgrid varchar(10) NOT NULL,
  qty` int(11) NOT NULL,
  PRIMARY KEY (empid)
);

INSER INTO salses VALUES('A',Z',300);
INSER INTO salses VALUES('B',X',100);
INSER INTO salses VALUES('C',Y',100);
INSER INTO salses VALUES('D',Z',300);
INSER INTO salses VALUES('E',X',200);
INSER INTO salses VALUES('F',Z',100);

SELECT empid,
 (SELECT COUNT(*) FROM sales AS T2 
WHERE T2.empid <= T1.empid) AS rownum 
FROM sales AS T1;