wow sub count

1) count (1) compared to COUNT (*):1. If your data table does not have a primary key, then count (1) is faster than COUNT (*)2, if there is a primary key, then the primary key (Union primary key) as the count of the condition is also faster than

The table structure is as follows: The code is as follows Copy Code Mysql> Show CREATE TABLE Userg;1. Row ***************************Table:userCreate table:create Table ' user ' (' ID ' int (a) unsigned not NULL auto_increment,' Name ' varchar not NULL,' pwd ' varchar not NULL,' Email ' varchar not NULL,' Phone ' varchar not NULL,' Sex ' enum (' F ', ' M ', ' n ') not NULL DEFAULT ' n ',' addres ' varchar not NULL,' tag ' varchar not NULL,PRIMARY KEY (' id '),KEY ' na

The table structure is as follows:Mysql> Show CREATE TABLE user\g;*************************** 1. Row *************************** table:usercreate table:create Table ' user ' ( ' id ' int (ten) unsigned not NULL AUTO _increment, ' name ' varchar (NOT null), ' pwd ' varchar (') ' is not null, ' email ' varchar (+) NOT NULL, ' Phone ' varchar ' NOT null, ' sex ' enum (' F ', ' M ', ' n ') is not null DEFAULT ' N ', ' addres ' varchar (+) NOT null, ' t AG ' varchar ' not NULL, PRIMARY

Either count (*) or COUNT (1) or count ([column]) in SQL Server is perhaps the most commonly used aggregate function. Many people actually distinguish between the three. This article will explain the role of these three, relations and the underlying principles. I often see some so-called optimization recommendations that use

Tags: Oracle countAfter listening to nearly 20 speeches in the last two days, I felt a lot of harvest, and the deepest feeling was that I still had a long way to go. There are several points to note:Listening to the old cat yesterday, it is a common problem that Oracle has a problem with count (*), COUNT (1), and count (primary key). This question seems very simp

Label:The difference between count (1) count (*) count (field) usage in SQL statementsThe Count function is one of the most commonly used functions in SQL statements, and the Count function is a function of the number of records in the statistics table.A. The difference betw

Let's take a look at the description of Count (*) and Count (col) in Bol:COUNT(*Returns the number of items in the group. IncludingNULLvalues and duplicates. COUNT( Allexpression) evaluates expression for each row in the group and returns the number of non-null values . Expression in addition totext、ImageOrntextAn expression of any type other than. The use of agg

Tags: style http color using AR strong data div problemCount () differs from sum () in MySQLFirst, create a table to illustrate the problem create table ' result ' (' name ' varchar () default NULL, ' subject ' varchar () default NULL, ' Score ' tinyint ( 4) Default NULL) Engine=myisam default Charset=utf8 inserts some data, insert into result values (' Zhang San ', ' math ', 90), (' Zhang San ', ' language ', 50), (' Zhang San '), ' geography ', 40), (' John Doe ', ' language ', 55), (' John Do

Statistical functions of SQLsql统计函数有 count 统计条数，配合group用 sum 累加指定字段数值但注意sum（1）就特殊SUM (1) equals count (*) sum（1）统计个数，功能和count（*）一样，但效率上count（*）高。所以尽量少用。Give me a little example.SELECT ad_network_id,,sum(1),count(*),sum(2),count