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This article mainly introduces "what is the relationship between the table and the database". In the daily operation, I believe that many people have doubts about the relationship between the table and the database. The editor consulted all kinds of data and sorted out a simple and easy-to-use method of operation. I hope it will be helpful to answer the question of "what is the relationship between the table and the database"! Next, please follow the editor to study!

The relationship between a table and a database is that a database can contain multiple tables. TABLE is the object used to store data in the database, is the collection of structured data, and is the foundation of the whole database system. Each database is composed of several data tables; in other words, data cannot be stored in the database without data tables.

The operating environment of this tutorial: windows7 system, mysql8 version, Dell G3 computer.

TABLE is the object used to store data in the database, is the collection of structured data, and is the foundation of the whole database system. A table is a database object that contains all the data in the database.

Data table is an important part of database, and each database is composed of several data tables. In other words, you cannot store data in a database without a data table.

For example, to create an empty folder on your computer, if you want to store "Hello C Chinese net" in the folder, you must write it in an Word document, notepad, or other document that can store text. The empty folder here is the equivalent of a database, and the document that holds the text is the equivalent of a data table.

A table is defined as a collection of columns. Like a spreadsheet, data is organized in a table in row and column format. Each column in the table is designed to store some type of information (such as date, name, dollar amount, or number). There are several controls on the table (constraints, rules, default values, and custom user data types) to ensure the validity of the data.

MySQL create data Table (CREATE TABLE statement)

After you create the database, the next step is to create the data table in the database. The so-called creation of data tables refers to the creation of new tables in the database that has already been created.

The process of creating a data table is not only the process of specifying the attributes of the data column, but also the process of implementing data integrity (including entity integrity, referential integrity, and domain integrity) constraints.

Basic grammar

In MySQL, you can use CREATE TABLE statements to create tables. Its grammatical format is:

CREATE TABLE ([Table definition options]) [Table options] [Partition options]

The format of "Table definition options" is:

[,...]

There are many syntax for CREATE TABLE command, which is mainly composed of table creation definition (create-definition), table option (table-options), and partitioning option (partition-options).

Here we first describe a simple example of creating a new table, and then focus on some of the main syntax points in the CREATE TABLE command.

The main syntax and usage instructions of the CREATE TABLE statement are as follows:

CREATE TABLE: used to create a table with a given name, you must have permission for the table CREATE.

Specifies the name of the table to be created, given after CREATE TABLE, and must conform to the naming convention for identifiers The table name is specified as db_name.tbl_name to create the table in a specific database. It can be created in this way, regardless of whether there is a current database or not. You can omit db-name when you create a table in the current database. If you use a quoted distinguished name, the database and table names should be in quotation marks, respectively. For example, 'mydb'.'mytbl' is legal, but' mydb.mytbl' is illegal.

A table creation definition consisting of a column name (col_name), a column definition (column_definition), and a possible null value description, integrity constraint, or table index

By default, the table is created into the current database. An error occurs if the table already exists, there is no current database, or the database does not exist.

MySQL ALTER TABLE: modifying data tabl

The premise of modifying a data table is that the table already exists in the database. Modifying a table refers to modifying the structure of a data table that already exists in the database. The operation of modifying the data table is also essential in database management, just like drawing a sketch, you can erase it with an eraser if you draw too much, and add it with a pen if you draw less.

Not knowing how to modify the data table is equivalent to throwing away the redrawing as soon as we make a mistake, which increases the unnecessary cost.

In MySQL, you can use ALTER TABLE statements to change the structure of the original table, such as adding or deleting columns, changing the original column type, renaming columns or tables, and so on.

The syntax format is as follows:

ALTER TABLE [modify options]

The syntax format of the modification option is as follows:

{ADD COLUMN

| | CHANGE COLUMN |

| | ALTER COLUMN {SET DEFAULT | DROP DEFAULT} |

| | MODIFY COLUMN |

| | DROP COLUMN |

| | RENAME TO |

| | CHARACTER SET |

| | COLLATE} |

MySQL delete data table (DORP TABLE statement)

In the MySQL database, we can delete tables from the database that are no longer needed.

When deleting the table, the structure of the table and all the data in the table will be deleted, so it is best to back up the data table before deleting it, so as to avoid irreparable losses.

Let's take a look at how to delete data tables in the MySQL database.

Basic grammar

Use the DROP TABLE statement to delete one or more data tables in the following syntax format:

DROP TABLE [IF EXISTS] Table name 1 [, Table name 2, Table name 3.]

The syntax format is described as follows:

Table name 1, table name 2, table name 3. Represents the name of the data table to be deleted. DROP TABLE can delete multiple tables at the same time, as long as the table names are written after each other and separated by commas.

IF EXISTS is used to determine whether a data table exists before it is deleted. Without IF EXISTS, MySQL will prompt an error when the data table does not exist and interrupt the execution of the SQL statement; with IF EXISTS, the SQL statement can be executed smoothly when the data table does not exist, but will issue a warning (warning).

At this point, the study of "what is the relationship between the table and the database" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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