Plsql_ Basic Series 3_ merge operation Union/union All/minus/interset

2014-11-30 Baoxinjian

I. Summary

If we need to display the results of the two SELECT statements as a whole, we need to use the union or UNION ALL keyword. Union (or union) is the function of merging multiple results together to display them.

The difference between Union and union all is that union automatically compresses duplicate results in multiple result sets, and union ALL displays all results, whether duplicates or not.

• Union: Set operation on two result sets, excluding duplicate rows, and sorting the default rules;
• Union All: Set operation on two result sets, including repeating rows, without sorting;
• Intersect: The intersection of two result sets, excluding duplicate rows, and sorting the default rules;
• Minus: Differential operation on two result sets, excluding duplicate rows, and sorting the default rules;

The ORDER BY clause can be specified in the last result set to change the ordering method.

Ii. UNION

Third, UNION all

Iv. minus

Wu, Interset

Plsql_ Basic Series 3_ merge operation Union/union All/minus/interset