1. Exceptions to semicolons
For MySQL, the first thing you have to keep in mind is that each line of the command is separated by a semicolon (;) As the end, but ... There is no absolutely absolute thing, also here, when a line of MySQL is inserted in 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 is also a semicolon as the end of a line, the extra semicolon sometimes makes PHP parser can not understand, so it is good to omit. In this case, although the semicolon is omitted, PHP will automatically help you when executing the MySQL command.
There is also a case where no semicolon is added. You can use G to end a row of SQL statements when you want to display the vertical of the field, rather than the usual arrangement, and then use a semicolon, for example:
SELECT * from penpals WHERE user_id = 1G
2. TEXT, DATE, and SET data types
A field in a MySQL data table must have a data type defined. There are about 25 options, most of which are straightforward and not much of a waste of breath. But there are a few that need to be mentioned.
TEXT is not a data type, although it may be said in some books. It should actually be "LONG VARCHAR" or "Mediumtext".
The format of the 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")
Also, you can subtract between data types to get the difference in number of days:
$age = ($current _date-$birthdate);
Set set is a useful data type that is somewhat similar to enum enum, except that set can hold multiple values and ENUM can hold only one value. Moreover, the SET type can only have up to 64 predetermined values, while the ENUM type can handle up to 65,535 predefined values. What if you need a collection of more than 64 values? At this point, you need to define multiple collections to solve this problem together.
3. Wildcard characters
There are two types of wildcard characters for SQL: "*" and "%". are used in different situations respectively. For example: If you want to see all the contents of a database, you can query it like this:
SELECT * from dbname WHERE user_id like '% ';
Here, two wildcard characters are used. They mean the same thing?? are used to match any string, but they are used in a different context. "*" is used to match the field name, while "%" is used to match the field value. Another area that is not easily noticed is that the "%" wildcard needs to be used with the LIKE keyword.
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