Some issues that need to be paid attention to when operating MySQL database in PHP (translated) Some issues are very well said. . Quite novel. . -Database related_PHP tutorial

Some issues to pay attention to when operating MySQL database in PHP
1. Semicolon exceptions
For MySQL, the first thing you must remember is that each line of commands ends with a semicolon (;) , but... there is no absolute thing, and it is the same here. When a line of MySQL is inserted into the PHP code, it is best to omit the following semicolon, for example:
mysql_query ("INSERT INTO tablename (first_name, last_name)
VALUES ('$first_name', '$last_name')
");
This is because PHP also ends a line with a semicolon, and extra semicolons sometimes make PHP's syntax The parser doesn't understand it, so it's better to omit it. In this case, although the semicolon is omitted, PHP will automatically add it for you when executing the MySQL command.

There is another situation where you don’t need to add a semicolon. When you want to display the vertical arrangement of the fields you want instead of the usual horizontal arrangement, you can use G to end a line of SQL statements. In this case, there is no need for a semicolon, for example:
SELECT * FROM PENPALS WHERE USER_ID = 1G  
2. TEXT, DATE, and SET data types  
The fields of the MySQL data table must have a data type defined. There are about 25 options, most of which are straightforward and require no further explanation. But there are a few that need to be mentioned.

TEXT is not a data type, although some books may say so. It should actually be "LONG VARCHAR" or "MEDIUMTEXT".

The format of DATE data type is YYYY-MM-DD, for example: 1999-12-08. You can easily use the date function to get the current system time in this format:
date("Y-m-d")
Moreover, you can subtract between DATA data types to get the difference in days:
$age = ($current_date - $birthdate);
Set SET is a useful data type. It is somewhat similar to enumeration ENUM, except that SET can save multiple values ​​and ENUM can only save one value. Moreover, the SET type can only have a maximum of 64 predefined values, while the ENUM type can handle a maximum of 65,535 predefined values. And what if we need a collection with more than 64 values? At this time, you need to define multiple collections to solve this problem together.

３. Wildcard