1c51e91292
1. Corrected NOT NULL / NULL explanation 2. Added explanation for Default 3. Added new columns to illustrate 'default' and 'null' behaviour. 4. Explanations for datatypes 5. NUMERIC Datatype illustrated.
71 lines
2.8 KiB
Markdown
71 lines
2.8 KiB
Markdown
---
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title: SQL Create Table Statement
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---
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## SQL Create Table Statement
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<!-- The article goes here, in GitHub-flavored Markdown. Feel free to add YouTube videos, images, and CodePen/JSBin embeds -->
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A table is a group of data stored in a database.
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To create a table in a database you use the `CREATE TABLE` statement. You give a name to the table and a list of columns with its datatypes.
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##### SYNTAX #####
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```sql
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CREATE TABLE table_name(Attribute1 Datatype,
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Attribute2 Datatype,
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........);
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```
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here:
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* Attribute1, Attribute2... -> Column Name
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* Datatype... -> type of value you want to column have. For eg. int(size), char(size), Varchar(size),etc.
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Here’s an example creating a table named Person:
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```sql
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CREATE TABLE Person(
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Id int not null,
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Name varchar not null,
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DateOfBirth date not null,
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Gender bit not null,
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Height numeric(5, 2) default 0 not null,
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Weight numeric(5, 2) default 50,
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WaistSize numeric(5, 2),
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PRIMARY KEY( Id )
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);
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```
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##### PrimaryKey
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In the example above, each Person has a Name, Date of Birth, Gender and Height. The Id column is the key that identifies one person in the table. You use the keyword `PRIMARY KEY` to configure one or more columns as a primary key.
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##### Datatypes
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Each column also has it's datatype mentioned.
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Just to understand the above code, the datatype mentioned indicates the following type of values approximately.
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```
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int : A whole number
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varchar : Strings
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date : A Date Value without Time component
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bit : A Boolean value
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numeric(5, 2): A decimal value with ( Precision 5 and Scale 2 )
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ie. Total of 5 digits with 3 digits before the decimal point and 2 digits after decimal point.
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```
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Proper List and meaning of datatypes can be refered from resources like this: ( https://www.w3schools.com/sql/sql_datatypes.asp )
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##### Default and Not NULL
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When a row of values are inserted into a table, any column which is marked as `not null` and without a `default` value will be compulsary. Insert fails otherwise.
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If no value is provided for a column which has a `default` value, insert will succeed with the column being assigned the default value defined in the table definition.
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>e.g Column Weight has default value as 50.
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By default all columns are nullable ie. `null` is assumed unless explicity set as `not null`. So any column without `default` and `not null` keyword can be skipped in insert commands. They will have *null* value on querying.
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>e.g Column WaistSize can be *null*
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>Please note that `null` and `` (Blank) are queried and handled differently in most Databases.
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#### More Information:
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<!-- Please add any articles you think might be helpful to read before writing the article -->
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[SQL | CREATE](https://www.geeksforgeeks.org/sql-create/)
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