PHP + MySQL calculates the number of records for each table in the database and sorts the records in descending order. PHP + MySQL calculates the number of records for each table in the database and sorts the records in descending order, mysql
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>
Problem description
In the production database, the data of one table is 1 billion level, and that of the other table is 10 billion level. The data of other tables is also quite large. I didn't know that these tables had such a large amount of data
Original post address: http://www.cnblogs.com/phpliu/archive/2010/06/21/1761726.html
For example:ID name value1 A PP2 A PP3 B III4 B PP5 B PP6 c pp7 c pp8 C IIIID is the primary keyThis result is required.ID name value1 A PP3 B III4 B PP6 c pp8 C
Share the following method of deleting duplicate records in a database with an SQL statement.For example, there is now a person table (table name: peosons)If you want to name, ID, address, the three fields exactly the same record querySelect p1.*
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
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
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
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
SqlCOUNT () function
The count () function returns the number of rows that match the specified criteria.
SQL COUNT (column_name) syntaxThe count (column_name) function returns the number of values for the specified column (NULL does not
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