what index of array

basic functions of array manipulationThe key name and value of the arrayArray_values ($arr); Gets the value of the array Array_keys ($arr), gets the key name of the array array_flip ($arr), and the values in the array are exchanged with the key

Basic functions of array manipulationThe key name and value of the arrayArray_values ($arr); Get the value of an arrayArray_keys ($arr); Gets the key name of the arrayArray_flip ($arr); the values in the array are exchanged with the key names (if

1. The concept of arrays An array is a named range that is used to store a series of variable values. Each array element has an associated index (also a keyword) that can be used to access elements. PHP allows you to use numbers or strings evenly

Php array declaration, traversal, array global variables. Php Tutorial array declaration, traversal, array global variable [php]? ** 1. Array Overview * 1. the essence of arrays: managing and operating a group of variables, batch processing * 2.

_ Id Index An index is automatically created for the _ id field for all sets except the set of capacity. This is a special index and cannot be deleted. The _ id index forces that its keywords are unique (except for some scenarios in the partition

This article mainly originates from the Internet mainstream article, just according to the individual understanding slightly makes the integration, behind has the reference link. I. Summary This paper takes the MySQL database as the research object

First, the index introductionIn MongoDB, indexes are used to support efficient queries. If there is no index, MONGODB must scan each document in the entire collection to find a matching document. However, if an appropriate index is established,

The main considerations for designing SQL Server indexes are as follows:Check where condition and join condition column;Use narrow index;Check the selectivity of the column;Check the data type of the column;Consider the order of the columns;Consider

PHP has a lot of functions about arrays to facilitate array manipulation. Defined: Each entity of an array contains two items: key and value, which can be retrieved by a query key. These keys can be numeric (numerical) or associated (associative)

The main considerations for designing SQL Server indexes are as follows:Check where condition and join condition column;Use narrow index;Check the selectivity of the column;Check the data type of the column;Consider the order of the columns;Consider