select count

AIn general, select COUNT (*) and select COUNT (1) both return the same resultIf the table does not have a primary key (Primary key), then count (1) is faster than COUNT (*),If there is a primary key, the primary key is the fastest when the

Generally, the returned results are the same for select count (*) and select count (1 ). If the table does not have a primary key, count (1) is faster than count, If a primary key exists, the count (primary key) is the fastest when the primary key

In general, select COUNT (*) and select COUNT (1) both return the same resultIf the table does not have a primary key (Primary key), then count (1) is faster than COUNT (*),If there is a primary key, the primary key is the fastest when the condition

In general, select COUNT (*) and select COUNT (1) are returned with the same result. If the table does not have a primary key (Primary key), then count (1) is faster than count (*). If there is a primary key, the primary key is the fastest as

To count how many rows of data a table T has, the usual notation is:Query A:select Count (*) from TBut you can also use the following statement to check:Query B:select count (1) from TThe results are usually the same. So where is the difference?If

  1. select count (*) FROM tablename is the optimal choice under any circumstances; 2. Minimize select count (*) FROM tablename where col = 'value' queries; 3. prevent the appearance of select count (COL) FROM tablename.     COUNT (*) and COUNT (COL)

1. Test Environment OS: LinuxDB: mysql-5.5.18Table: innodb Storage Engine The table is defined as follows: 2. test scenario and analysis [number of group_message records in the statistical table] (1) select count (*) Method (2) select count

1. Test environment Os:linuxdb:mysql-5.5.18TABLE:INNODB Storage Engine The table is defined as follows: 2. Test scenario and analysis "number of records Group_message" (1) Select COUNT (*) method (2) Select COUNT (1) method (3) Select

First, the questionToday there is a magical problem-there is data in the table, but the result of select COUNT (*) is 0.The initial manifestation of the problem is that the query report has no paging.At first, I thought it was a Java-side problem.

SQL Server Databasethe Count () function returns the number of rows that match the specified criteria. The syntax SQL count (column_name) syntax count (column_name) function returns the number of values for the specified column (NULL does not count

I want to count the number of fields a in a table. Because field a has repeated records, I want to exclude repeated records. The SQL statement is: Select count (distinct)   Link: http://www.w3school.com.cn/ SQL/SQL

This article mainly introduced the ASP to obtain the SELECT Count statement return value method, generally uses in the statistical data use the SELECT Count statement, obtains the query to the row number, needs the friend to be possible to refer to

Questions about SELECT COUNT (*)! For example, table structure and data are as follows: ID typeid Name 1 2 A 2 2 b 3 3 C 4 3 D I want to implement select COUNT (*) as nums ... where typeid=2 and the name of each record, that is, all

Thinking about orcle 11g select count (*) from v $ lock, orcle11g recently, we found that the query by orcle 11g select count (*) from v $ lock is very slow, and I think it is necessary to perform a detailed analysis: select count(*) from v$lock;--

Select count (*) requires a full table scan to return the number of rows in the table. This is a very time-consuming operation for a table with a large data size. To obtain the number of all rows in a table, consider the alternative solution

Test table: StudentSelect from Studnet;Select Count (distinct from student;Select Count (distinct from student;This is wrong, can be adapted to achieveSelect Count from (Selectdistinct from student) St; Blocked, I'm going the other way!SQL Server

We use the Select COUNT (*) statement when we generally count database records, and when we use Query Analyzer for SQL Server, the direct input to the SELECT count (*) from table name counts the records in the table. But how do we return the value

The difference between Select count (*) and Count (1) in SQL server and the execution method, selectcount In SQL Server, Count (*), Count (1), or Count ([column]) is perhaps the most common aggregate function. Many people cannot tell the difference

Hours server queries the number of coaches, use the Select COUNT (Distinct (U_strno)) times to exceed memory errors. After reference "Mysqld-nt:out of memory Solution"

Create Table yw (ID int unsigned NOT NULL auto_increment,c1 int NOT NULL default ' 0 ',C2 int NOT null default ' 0 ',Primary KEY (ID));Creating a stored procedure call insert_yw inserting data into a tableTwo parameters to improve insert performance