Aggregate functions often need to add a GROUP BY statement, Aggregate function is often said poly and function, also called aggregate functions
GROUP BY statement commonly used with aggregate functions (COUNT, MAX, MIN, SUM, AVG), according to one or more columns of the result set grouping.
grammar:
select aggregate function (field), from table Group by field
Build a table, get points, in order to facilitate comparison
Grouped query banking statistics of the same name a few
SELECT COUNT (field) AS number, a field from table Group by field a
Which count in the field free to fill in, generally id
Possible error:
That field only and grouping queries can not aggregate functions
You can be slightly modified:
Check bank group, and the total number of wage statistics
The top one query
grammar:
SELECT Top front query lines COUNT (field) AS number, a field from table Group by field a
And the sort order by a
Syntax: Field to be consistent
SELECT Top front query lines COUNT (field) AS number, field A from table Group by field A Order by field A desc
If not
And where the words using a
Syntax: count () there is no limit, put consequently the line
SELECT Top front query lines COUNT ( 0 ) AS number, field A from table where conditions Group by field A Order by field A desc
Multi-table query
grammar:
SELECT table 1.name, COUNT (Table 2.aid) the AS the nums the FROM Table 2 the INNER the JOIN Table. 1 the ON Table 2.site_id = Table 1.id the GROUP BY table 1.name;
the SELECT * from obgetest - grouping query Bank ,, which is the name of two obge the SELECT COUNT (Gids) AS number, Bank from obgetest Group by Bank - - As can be seen, when multiple fields, only to be grouped query fields that can not use aggregate functions the SELECT COUNT (Gids) aS number, Bank, Gongzi from obgetest Group by Bank - can modify the query packet banks, and the total wage statistics the total number of the SELECT COUNT (Gids) aS number, Bank, SUM (Gongzi) AS total from obgetest Group byBank - and a top query, count field bank and placed inside the field of action consistent gids SELECT top . 5 COUNT (Bank) AS number, Bank from obgetest Group by Bank - one with the order by, the same number inquiry packet wages and in accordance with the reverse order, check before row 5 - --- must pay attention field and packet field to be consistent ordering SELECT Top 5 COUNT (REM) AS number, Gongzi from obgetest Group by Gongzi Order by Gongzi desc - - there is an error the SELECT Top 5 COUNT (REM) ASNumber, Gongzi from obgetest Group by Gongzi Order by Gids desc - - Note that the syntax and the position where the words SELECT COUNT ( 0 ) AS number, Gongzi from obgetest where Gongzi > 1000 Group by Gongzi Order by Gongzi desc