SQL-TEXT, DATE and SET data types in MySQL_PHP tutorial

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

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

DATE

DATE data type format 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")

And, you can subtract between DATA data types to get the difference Number of days in time:

$age = ($current_date - $birthdate);

SET

Set SET is a useful data type, it It is somewhat similar to the 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.

Wildcard

There are two types of wildcard characters in SQL: "*" and "%". Used in different situations. For example: If you want to see all the contents of the database, you can query like this:

SELECT * FROM dbname

WHERE USER_ID LIKE '%';

Here, two wildcards are used. They mean the same thing - they both match any string - but they are used in different contexts. " * " is used to match field names, and " % " is used to match field values. Another thing that is not easy to notice is that the "%" wildcard character needs to be used together with the LIKE keyword.

There is also a wildcard character, which is the underscore "_". It has a different meaning from the above and is used to match any single character.

(T115)

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