Difference between single quotes and double quotes in php

In PHP, you can use single quotes or double quotation marks ;". In PHP, you can use single quotation marks ''or double quotation marks" "to define strings "".

However, the same single or double quotation marks must be used to define strings. for example, 'Hello World "and 'Hello world' are invalid strings.

What is the difference between single quotes and double quotes?

PHP allows us to directly include string variables in double quotation marks.

The content in a single quotation mark string is generally considered a common character, so the content in a single quotation mark is not escaped more efficiently.

For example:

$ Str = 'hello'; echo "str is $ str"; // running result: str is helloecho 'Str is $ str '; // running result: str is $ str

In php, variables ($ var) and special characters (\ r \ n) in double quotes are escaped, and the content in single quotes is not escaped (so it is more efficient ).

In use, I used to like to write $ SQL = "SELECT * FROM table WHERE id = $ id" in the SQL string, so that the $ id in it can be escaped, single quotes won't work.

There is no difference between single quotes and double quotes in JavaScript, as long as they are used in pairs.

Most of the single quotes I use in JavaScript are Because Javascript has a lot of dealings with HTML. When outputting HTML fragments, you do not need to escape the attribute quotation marks in HTML.
In short, it depends on the actual situation and how to use it conveniently.