GBase 8s V8. 8 SQL Guide: Tutorial - 6.1.1 (1)

6.1.1 GROUP BY Clause
GROUP BY Clause divides the table into groups . This clause is usually associated with the aggregate function group that generates the summary value for each such group
close . To write SELECT Some examples in the statement show the usage of aggregate functions applied to the entire table . This chapter should explain
Aggregation function for row groups .
Use without aggregation GROUP BY Clause and in SELECT Used in clauses DISTINCT（ or UNIQUE）
Keywords are very similar . The following queries are described in selecting specific columns .
chart : Inquire about
SELECT DISTINCT customer_num FROM orders;
You can also write this statement according to the following query .
chart : Inquire about
SELECT customer_num FROM orders
 GROUP BY customer_num;
chart 1 Sum graph 2 Return the following lines .
chart : Query results
customer_num 
 
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GROUP BY Clause collects rows into groups , Therefore, each line in each group has the same customer number . There is no choice
In the case of any other column , The end is the only customer_num List of values .
GROUP BY The function of clause is more obvious when it is used with aggregate function