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MySQL TEXT, DATE, SET data types (to) [@ more@] the fields of the MySQL data table must have a data type defined. There are about 25 options, most of which are straightforward, so don't waste your 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 data types to get the time days of the difference:

$age = ($current_date-$birthdate)

The collection SET is a useful data type, which is somewhat similar to enumerating ENUM, except that SET can hold multiple values while ENUM can hold only one value. Furthermore, the SET type can only have up to 64 predetermined values, while the ENUM type can handle up to 65535 predefined values. What if you need a collection of more than 64 values? At this point, multiple sets need to be defined to solve the problem together.

Wildcard character

There are two types of SQL equivalents: "*" and "%". They are used in different situations. For example, if you want to see all the contents of the database, you can query it like this:

SELECT * FROM dbname WHERE USER_ID LIKE%

Here, both wildcards are used. They mean the same thing. Are used to match any string, but they are used in different contexts. "*" is used to match the field name, and "%" is used to match the field value. Another area that is not easy to notice is that the "%" wildcard needs to be used with the LIKE keyword.

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

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