SQL grouping functions for Oracle databases

The grouping Function Definition of SQL grouping functions in Oracle databases is different from that of single-row functions. Grouping Functions Act on a group of records and each group returns a result. This group can be an entire table or a group by clause that divides the table into multiple groups. Commonly used grouping function ● COUNT ({*/[distinct/all] express}): number of returned records. The express value here is non-null, * indicates all selected records, including duplicate and NULL. distinct indicates removing duplicate, and all indicates all but not NULL. [SQL] select count (all mgr) from emp; -- 13 select count (*) from emp; -- 14 select count (distinct mgr) from emp; -- 6 ● the maximum and minimum values of MAX and MIN expressions (same as the preceding parameters) Ignore null values [SQL] select max (distinct mgr) from emp; ● AVG returns the average value and ignores NULL values, because of its null value, it cannot be used to calculate [SQL] select avg (sal) from emp; ● SUM: sum [SQL] select SUM (sal) from emp; these grouping functions are very useful in practical applications! You can perform statistics on relevant data!