select count 1

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

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) 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

Count (1) is actually to calculate the total number of qualified rows. 1 does not represent the first field, but a fixed value. In fact, you can think of such a field in the table. This field is a fixed value of 1, count (1), that is, to calculate

I. User table information     Ii. Conclusion   Use the query statement: Select count (1) from user; Use the explain statement to check whether the statement is indexed. the following result shows the query time of the statement. Data Volume query

The function is to calculate how many rows match a condition.1 does not represent the first field, but rather represents a fixed value, count (1) and COUNT (2) effect are the sameCount (*), the execution of the asterisk will be translated into the

Source from: http://hwhuang.javaeye.com/blog/650903 KeywordsConcepts of nested transactions and autonomous transactionsUse of nested transactionsUse of autonomous transactions1. Concepts1. nested transaction ):It refers to one or more sub

This section focuses on the principles and usage of in, as well as the common erroneous viewpoints. First, in the useUse of 1.1 inThe 1.1.1 and outer Two Table association fields are not emptySql> select * from TB1;T1 NAME1---------- ----------1 12

The paging stored procedures are roughly the following 1. Use not in and select top 2. Use ID greater than number and select top 3, using the cursor in SQL 4. Temporary table You can see the following links on the web Summary of common paging

Top, bottom, and average statements for SQL queriesWe're going to use it as an example of student achievement./*Structure Student tableStudent (s#,sname,sage,ssex)--s# student number, sname student name, Sage birth date, ssex student gender--2.

For SQL queries with the highest score, lowest score, and average score, take the Student score as an example. * structure Student table Student (S #, Sname, Sage, Ssex) -- S # Student ID, sname Student name, Sage year of birth, Ssex Student gender-2

Instr and like are all functions implemented by Oracle. In strict terms, instr is an internal function and like is an SQL standard, which is highly efficient. However, I do not know how to implement them yet. But both Instr and like are all

Experiment: A partition data block is corrupted and the partition table data is not fully recoveredBackground: The database does not have a valid backup and a partition has corrupted data blocks.Requirement: Maximum recovery of this partition

Using UltraEdit to quickly analyze the number of records in an Oracle table sometimes you need to view the number of records in a batch of tables in the Oracle database, such as data conversion and data verification scenarios. Method 1: Perform

Java training, Android training, iOS training,. NET training, look forward to communicating with you!Problems encountered with the "Unable to attach database" procedure:1, the data file itself, with access rights restrictions----Select the folder

Before doing the product horizontal display, have seen the comments said to use the cross-table.The company recently needed to make a data summary of the order form, and colleagues gave a reference to the SQLSELECT * FROM (select COUNT (1) as is

createtime--2017 June 1 14:36:37Author:marydonOne, SQL statements(b) Promotion1.2.1 Left connection + paged querySituation: the class table and the student table are related to each other, query the student information and the classMethod One: Use

Split function One:String segmentation:Create or Replace function get_strarraylength(Av_str VARCHAR2,--the string to be splitAv_split VARCHAR2--Separator symbol)return numberIsLv_str VARCHAR2 (1000);Lv_length number;BeginLv_str:=ltrim (RTrim (AV_STR)