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"MySQL optimization" MySQL count (*), COUNT (1), COUNT (primary key field), count (non-primary key field) which performance is best

The test results are: count (*) and COUNT (1) are basically equal, count (non-primary key field) is the most cost-consuming--Data Volume 708254Select COUNT (*) from tmp_test1;--avg 0.2240.2290.2190.2270.2220.2150.2240.2250.2210.2400.219Select COUNT (1) from tmp_test1;--avg 0

The execution difference between count (1), COUNT (*) and Count (column name)

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

The difference between count (1), COUNT (*), and count (column name) functions in Oracle

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 difference between Select count (*), COUNT (1), and count (columns) and how they are executed _mssql

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

Oracle in Count (1), COUNT (*) and COUNT (primary key) which is faster

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

The difference between count (1) count (*) count (field) usage in SQL statements

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

With Count (*) or count (column name) | | Count () differs from sum () in MySQL

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

About database Optimization The difference between count (1), COUNT (*), and count (column name), and questions about the order of fields in the table

Tags: unable to images creat upd introduction logs question purge SRC1. 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

Usage differences for COUNT (ID) count (1) count (*) in MySQL

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 difference between count (Primary_key), COUNT (1), COUNT (*) in MySQL

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

In SQL Server, the comparison of Count (*), Count (Col), Count (1)

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

The odd sum in SQL (1), SUM (2), COUNT (1), COUNT (6), COUNT (*): Total statistics

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

Odd sum (1), sum (2), count (1), count (6), count (*) in SQL: Total number of statistics, sumcount

Odd sum (1), sum (2), count (1), count (6), count (*) in SQL: Total number of statistics, sumcountSQL statistical functions The SQL statistical function has count statistics, and uses sum to accumulate the specified field value with sum, but note that sum (1) is special.Sum (1) is equivalent to

Select count (*), Count (1), and Count (column)

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 ex

The difference between count (*), COUNT (1), and count (primary key)

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 table has a larger amount of data, using count (1) is more than using

Summary of differences between count (*), count (1), and count (col) in MySQL, mysqlcol

Summary of differences between count (*), count (1), and count (col) in MySQL, mysqlcol Preface The count function is a function used to count records in tables or arrays. count (*) returns the number of rows to be retrieved, whet

Count (*), the difference between count (1) and Count (column)

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

Count (*), COUNT (1) and count (field) differ

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 true that I remember wrong, it is evident that the code review how usefu

Oracle Count Millions paging query total count, total bar count optimization

Oracle Count Millions paging query total number of records, total bar count optimizationOracle Count millions query total number of records, total bar count optimizationRecently do a project, do paging, found that paging query speed is very slow, paging I do is two queries, one is the total number of queries, one is to

Differences and performance of count (1) count (*) count (col)

Analysis of the differences between count (1) count (*) count (col) and performance count (1) and count ), in addition, the count (col) statistics for all rows are performed for records whose col columns are not empty. If an index

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