Hur man skapar en databas i MySQL (Skapa MySQL tabeller)

Steg för att skapa databas i MySQL

A database in MySQL is a named container for tables, views, and related objects. You can create one in two ways:

1) Genom att köra en enkel SQL-fråga

2) Genom att använda forward engineering i MySQL Arbetsbänk

As SQL nybörjare, låt oss först titta på frågemetoden.

Hur man skapar en databas i MySQL

Så här skapar du en databas i MySQL:

CREATE DATABASE är SQL-kommandot som används för att skapa en databas i MySQL.

Imagine you need to create a database with the name “movies”. You can create a database in MySQL by executing the following SQL command.

CREATE DATABASE movies;

Note: You can also use the command CREATE SCHEMA instead of CREATE DATABASE.

The statement works only once. Running it again throws an error, so let’s improve the query with more parameters.

OM INTE FINNS

En enda MySQL server can hold many databases. When several people share that server, you may try to create a database with the name of an existing one.

OM INTE FINNS instructs the MySQL server to check for a database with the same name before creating it. The database is created only if the name is free; without this clause, MySQL ger ett fel.

CREATE DATABASE IF NOT EXISTS movies;

Once the database name is safe, the next decision is how MySQL should store and compare the text inside it.

Sortering och teckenuppsättning

A teckenuppsättning decides which characters a column can store, while a tione är uppsättningen av rules used in comparison and sorting. Both can be defined at four levels: server, database, table, and column.

The collation you choose depends on the character set. For instance, the latin1 character set uses the latin1_swedish_ci collation, which is the Swedish case-insensitive order.

CREATE DATABASE IF NOT EXISTS movies CHARACTER SET latin1 COLLATE latin1_swedish_ci;

For local languages such as Arabic or Chinese, select the Unicode utf8mb4 character set, which stores every Unicode character, including emoji. In MySQL 8.0 utf8mb4 is the default character set and utf8mb4_0900_ai_ci the default collation.

CREATE DATABASE IF NOT EXISTS movies CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci;

Du kan hitta listan över alla sorteringar och teckenuppsättningar här..

You can see the list of existing databases by running the following SQL command.

SHOW DATABASES;

With the database in place, you can now add the tables that will actually hold the records.

Hur man skapar en tabell i MySQL

The CREATE TABLE command is used to create tables in a database.

As the diagram shows, every table belongs to one database. Tables are created with the SKAPA BORD statement, which has the following syntax.

CREATE TABLE [IF NOT EXISTS] `TableName` (`fieldname` dataType [optional parameters]) ENGINE = storage Engine;

HÄR

• “CREATE TABLE” is responsible for the creation of the table in the database.
• “[IF NOT EXISTS]” is optional and only creates the table if no matching table name is found.
• “`fieldName`” is the name of the field, and “data Type” defines the nature of the data stored in it.
• “[optional parameters]” is extra information about a field, such as “AUTO_INCREMENT” or NOT NULL.
• “storage Engine” manages the table, normally InnoDB, which supports transactions and foreign keys.

MySQL Skapa tabellexempel

Nedan följer en MySQL example to create a table in a database:

CREATE TABLE IF NOT EXISTS `MyFlixDB`.`Members` (
  `membership_number` INT AUTO_INCREMENT ,
  `full_names` VARCHAR(150) NOT NULL ,
  `gender` VARCHAR(6) ,
  `date_of_birth` DATE ,
  `physical_address` VARCHAR(255) ,
  `postal_address` VARCHAR(255) ,
  `contact_number` VARCHAR(75) ,
  `email` VARCHAR(255) ,
  PRIMARY KEY (`membership_number`) )
ENGINE = InnoDB;

Obs: den korrekta MySQL keyword is AUTO_INCREMENT with an underscore. AUTOINCREMENT tillhör SQLite and raises a syntax error in MySQL.

Every column carries a data type, so choose carefully: neither underestimate nor overestimate the range of data you expect.

MySQL Datatyper

Data types define the nature of the data that can be stored in a particular column of a table.

MySQL har 3 main categories of data types, namely:

1. Numerisk
2. text
3. Datum Tid

Numeriska datatyper

Numeric data types are used to store numeric values. It is very important to make sure the range of your data is between the lower and upper boundaries of the numeric data type you pick.

Textdatatyper

As the data type category name implies, these are used to store text values. Always make sure the length of your textual data does not exceed the maximum length of the column.

Date and Time Data Types

Date and time data types store calendar and clock values in a fixed format, which keeps sorting and comparison reliable.

Andra datatyper

Apart from the above, there are some other data types in MySQL.

Now let’s see a query for creating a table which uses all the data types. Study it and identify how each data type is defined in the below create table MySQL exempel.

CREATE TABLE `all_data_types` (
    `varchar` VARCHAR( 20 )  ,
    `tinyint` TINYINT  ,
    `text` TEXT  ,
    `date` DATE  ,
    `smallint` SMALLINT  ,
    `mediumint` MEDIUMINT  ,
    `int` INT  ,
    `bigint` BIGINT  ,
    `float` FLOAT( 10, 2 )  ,
    `double` DOUBLE  ,
    `decimal` DECIMAL( 10, 2 )  ,
    `datetime` DATETIME  ,
    `timestamp` TIMESTAMP  ,
    `time` TIME  ,
    `year` YEAR  ,
    `char` CHAR( 10 )  ,
    `tinyblob` TINYBLOB  ,
    `tinytext` TINYTEXT  ,
    `blob` BLOB  ,
    `mediumblob` MEDIUMBLOB  ,
    `mediumtext` MEDIUMTEXT  ,
    `longblob` LONGBLOB  ,
    `longtext` LONGTEXT  ,
    `enum` ENUM( '1', '2', '3' )  ,
    `set` SET( '1', '2', '3' )  ,
    `bool` BOOL  ,
    `binary` BINARY( 20 )  ,
    `varbinary` VARBINARY( 20 )
) ENGINE = MYISAM;

Bästa metoder för att skapa en MySQL Databas

A few conventions keep your scripts readable:

• Use upper case letters for SQL keywords, i.e. “DROP SCHEMA IF EXISTS `MyFlixDB`;”
• End all your SQL commands using semicolons.
• Avoid using spaces in schema, table, and field names. Use underscores instead to separate schema, table, or field names.
• Prefer InnoDB over MyISAM for new tables, because InnoDB supports transactions, row-level locking, and foreign keys.

The query method is complete. The second route reaches the same database from a visual model instead of hand-written SQL.

Hur man skapar MySQL Workbench ER Diagram Forward Engineering

MySQL Arbetsbänk har verktyg som stöder forward engineering. Forward engineering is the technical term that describes the process of translating a logical model into a physical implementation automatically.

Vi skapade en ER-diagram i vår ER-modellering lesson. We will now use that ER model to generate the SQL scripts that will create our database.

Skapar MyFlix-databasen från MyFlix ER-modellen

Step 1) Open the ER model of the MyFlix database som du skapade tidigare.

Steg 2) Välj forward engineer

Click on the Database menu and select Forward Engineer.

Step 3) Connection options

The next window allows you to connect to an instance of MySQL server. Click on the stored connection drop-down list and select local host. Click Execute.

Step 4) Select the options shown below

Select the options shown below in the wizard that appears. Click Next.

Step 5) Keep the selections default and click Next

The next screen shows the summary of objects in our EER diagram. Our MyFlix DB has 5 tables. Keep the selections default and click Next.

Steg 6) Revse SQL-skriptet

The window below previews the SQL script that creates our database. Save the script to a *.sql file or copy it to the clipboard, then click Next.

Step 7) Commit progress

The window below appears once the database is created on the selected MySQL server instance. The tables from the ER model now exist physically on the server.

The database along with dummy data is attached. We will use this DB in the lessons that follow. Simply import it in MySQL Workbench to get started.

Klicka här för att ladda ner MyFlixDB

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