what count

1. The difference between count (1), COUNT (*), and count (column name)Believe that you are always at work, or in the study of Count () in the end how to use faster. There has been a lot of doubt, some people say that count (*) faster, some people

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

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 '

The number of records in the database table is: Sql> Select COUNT (*) from table_name t; COUNT (*)----------6873 1, using the statistical results of COUNT (*): Sql> alter session Set Nls_language = "American"; Session altered. Sql> set timing on;Sql>

Execution effect: 1. Count (1) and COUNT (*) when the table has a larger amount of data, using count (1) is more time-consuming than using count (*) when analyzing the table. From the execution plan, the effect of count (1) and COUNT (*) is the

SQL tuning is primarily about reducing the number of consistent gets and physical reads. COUNT (1) is compared with COUNT (*): If your datasheet does not have a primary key, then count (1) is faster than COUNT (*)If you have a primary key, the

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

Select count (*), Count (1), and Count (column) In SQL Server, Count (*), Count (1), or Count ([column]) is perhaps the most common aggregate function. Many people cannot tell the difference between the three. This article will explain the functions,

If NULL participates in the aggregation operation, all other aggregation functions except count (*) ignore null. Such as:ID DD1 E2 NULLSelect COUNT (*) from table--the result is 2Select COUNT (DD) from table---result is 1Efficiency issues:When the

Count1) with Count (*) Comparison: If your data table does not have a primary key, COUNT (1) than COUNT (*Fast If there is a primary key, then the primary key (the Federated primary key) as the count condition is also more than count (*) to be quick

The problem stems from a problem with the python-CN Mail List: http://groups.google.it/group/python-cn/browse_thread/thread/758891b4342eb2d9/92c12bf6acd667ac Interestingly, why is the result of SYS. getrefcount (11111111) in python2.4 2, but

Tested under MySQL 5.6.MyISAM Engine:When creating a data table, MySQL generates 3 files, respectively (table: Test):TEST.FRM, Test. MYD, Test. Myi file,TEST.FRM is the table structure, Test.myd is the file that holds the data, Test.myi is the file

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

[PHP source code reading] count function, php source code count function. [PHP source code reading] count function, php source code count function in PHP programming, when traversing the array, it is often necessary to calculate the length of the

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

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

[PHP source reading]count function, PHP source Count function In PHP programming, when iterating over an array, it is often necessary to calculate the length of the array as the judgment condition for the end of the loop, and in PHP the operations

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(5)from

In the impression, Count (key) is more efficient than count (*), so the number of rows is counted in the project in Count (field). In the code Reivew was pointed out that the application of count (*), and then checked, and did a simple test, it is

After 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