count number of values

ObjectiveThis is a very common requirement in this article, for example, we have a user-origin table that is used to mark the channel from which the user is registered. The table structure is as follows ...Origin is the source of the user, the value

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

The array_count_values () function of the php array function sequence counts the number of occurrences of all values in the array. Array_count_values () defines and uses the array_count_values () function to count the number of occurrences of all

Array_count_values () Definition and usage The Array_count_values () function is used to count the occurrences of all values in an array. This function returns an array whose key name is the value of the original array, and the key value is the

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

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

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

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

Count different values in a time span. The number of occurrences of the period. Here, I want to query the number of times that the periods field of each month has different values in one year. For example, in the-4 month, periods appears 3 times for