IN A TABLE HAVE ONE COLUMN PRIMARY KEY..IT WILL NOT ALLOWS NULL VALUES AND DUPLICATE VALUES..INSTEAD OF PRIMARY KEY WHY CANT WE USE UNIQUE AND NOT NULL.THESE TWO ALSO DOESNT ACCEPT NULL VALUES IN NOT NULL AND UNIQUE DOESNT ACCEPT DUPLICATE VALUES? SO WHAT IS THE DIFEERENCE BETWEEN(UNIQUE,NOT NULL) AND PRIMARY KEY??????

8 Answers   rsystems,

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4 Answers   HCL,

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7 Answers   EDS,

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3 Answers   HSBC,

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what is the difference between trigger and constraint?

3 Answers   HSBC,

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how to find the First and Last Observation from the table: Ex: OBS Name Sal Ans like: OBS Name Sal 105 E 5000--> 105 E 5000 102 B 2000 104 D 4000 103 C 3000 101 A 1000--> 104 D 4000

4 Answers  

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