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What will be the output of the following query? select replace(substr((dump(ename)),(instr((dump(ename)),' ',-1,1))),',',' ') "Value of ENAME" from emp;
value of ename---------------------- 83 77 73 84 72 65 76 76 69 78
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What is the difference between IN subselects and EXISTS subselect?
If there is an index on the attributes tested an IN is more efficient since DB2 uses the index for the IN. (IN for index is the mnemonic).
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What is a composite index and how does it differ from a multiple index?
A multiple index is not one index but two indexes for two different columns of a table. A composite index is one index made up of combined values from two columns in a table. If two columns in a table will often be accessed together a composite index will be efficient.