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SQL Create Table Statement

SQL Create Table Statement

A table is a group of data stored in a database.

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.

SYNTAX

CREATE TABLE table_name(Attribute1 Datatype,
                       Attribute2 Datatype,
                       ........);

here:

Attribute1, Attribute2... -> Column Name
Datatype... -> type of value you want to column have. For eg. int(size), char(size), Varchar(size),etc.

Here’s an example creating a table named Person:

CREATE TABLE Person(
  Id           int      not null,
  Name         varchar  not null,
  DateOfBirth  date     not null,
  Gender       bit      not null,
  Height       numeric(5, 2) default 0 not null, 
  Weight       numeric(5, 2) default 50,
  WaistSize    numeric(5, 2),
  PRIMARY KEY( Id )
);

PrimaryKey

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.

Datatypes

Each column also has it's datatype mentioned.

Just to understand the above code, the datatype mentioned indicates the following type of values approximately.

int          : A whole number
varchar      : Strings
date         : A Date Value without Time component
bit          : A Boolean value
numeric(5, 2): A decimal value with ( Precision 5 and Scale 2 ) 
              ie. Total of 5 digits with 3 digits before the decimal point and 2 digits after decimal point.

Proper List and meaning of datatypes can be refered from resources like this: ( https://www.w3schools.com/sql/sql_datatypes.asp )

Default and Not NULL

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.

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.

e.g Column Weight has default value as 50.

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.

e.g Column WaistSize can be null

Please note that null and `` (Blank) are queried and handled differently in most Databases.

More Information:

SQL | CREATE

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