Usage of distinct in Thinkphp

Classification and Usage Analysis of JSP Comments JSP comments are divided into two types: single-line comments: ending with, only a single line of code can be commented. Multi-line comments: starting with /* and ending with */, you can comment multiple lines of code. Single-line comment example Multi-line comment example/**This is a multi-line comment*Can comment on multiple lines of code*/Usage of JSP comments JSP comments can be used to comment JSP code to make it easier to read

Introduction to Python functions: Usage and examples of the isinstance function Python is a powerful programming language that provides many built-in functions to make programming more convenient and efficient. One of the very useful built-in functions is the isinstance() function. This article will introduce the usage and examples of the isinstance function and provide specific code examples. The isinstance() function is used to determine whether an object is an instance of a specified class or type. The syntax of this function is as follows

WPS is a commonly used office software suite, and the WPS table function is widely used for data processing and calculations. In the WPS table, there is a very useful function, the DATEDIF function, which is used to calculate the time difference between two dates. The DATEDIF function is the abbreviation of the English word DateDifference. Its syntax is as follows: DATEDIF(start_date,end_date,unit) where start_date represents the starting date.

Introduction to Python functions: usage and examples of the abs function 1. Introduction to the usage of the abs function In Python, the abs function is a built-in function used to calculate the absolute value of a given value. It can accept a numeric argument and return the absolute value of that number. The basic syntax of the abs function is as follows: abs(x) where x is the numerical parameter to calculate the absolute value, which can be an integer or a floating point number. 2. Examples of abs function Below we will show the usage of abs function through some specific examples: Example 1: Calculation

How to use the exit function in C language requires specific code examples. In C language, we often need to terminate the execution of the program early in the program, or exit the program under certain conditions. C language provides the exit() function to implement this function. This article will introduce the usage of exit() function and provide corresponding code examples. The exit() function is a standard library function in C language and is included in the header file. Its function is to terminate the execution of the program, and can take an integer

The ISNULL() function in MySQL is a function used to determine whether a specified expression or column is NULL. It returns a Boolean value, 1 if the expression is NULL, 0 otherwise. The ISNULL() function can be used in the SELECT statement or for conditional judgment in the WHERE clause. 1. The basic syntax of the ISNULL() function: ISNULL(expression) where expression is the expression to determine whether it is NULL or

Let’s talk about the general conclusion first: when the semantics are the same and there is an index: both groupby and distinct can use the index, and the efficiency is the same. In the case of the same semantics and no index: distinct is more efficient than groupby. The reason is that both distinct and groupby will perform grouping operations, but groupby may perform sorting and trigger filesort, resulting in inefficient SQL execution. Based on this conclusion, you may ask: Why are groupby and distinct efficient when they have the same semantics and indexes? Under what circumstances does groupby perform sorting operations? Find answers to these two questions. Next, let’s take a look at dist

Usage of Transform in CSS The Transform property of CSS is a very powerful tool that can perform operations such as translation, rotation, scaling and tilting of HTML elements. It can dramatically change the appearance of elements and make web pages more creative and dynamic. In this article, we will introduce the various uses of Transform in detail and provide specific code examples. 1. Translate (Translate) Translate refers to moving an element a specified distance along the x-axis and y-axis. Its syntax is as follows: tran