A primary key constraint is a key that has one or more columns to help identify each tuple or record in a table individually.

Qualities
Only distinct values should be assigned to the column designated as the primary key; duplicate values are forbidden. The primary key column contains no NULL values. As a result, there is a necessary value in the column holding the primary key. There is only one primary key per table, even if a primary key may contain more than one column.

Adding a new row using an existing primary key is not feasible.

categorized as,

• A single-column, basic primary key.
• Multiple columns make up the composite primary key.

As stated in the Make a Table or Modify a table statement.

A PRIMARY KEY constraint can be used to create the primary key in a table.

It can be created at a couple of levels.

• Column
• Table

SQL Primary Key at Column level
The primary key should be defined at the column level if it only has one column. The primary key "primary_field_name" is created in the table by the following code.

Syntax
Field_name data_type PRIMARY KEY

Example
CREATE TABLE Employee
(
  Id INT NOT NULL PRIMARY KEY,
  [Name] VARCHAR(50) NOT NULL,
  City VARCHAR(20) NOT NULL
)

Let’s verify the primary key with an example.
INSERT INTO Employee
VALUES (1, 'Peter', 'Scott');

Let’s try the execution of the same query again in SQL.

It will throw an exception.

Let’s try with the NULL inserted as the primary key value.
INSERT INTO Employee
VALUES (NULL , 'Peter', 'Scott');

It will throw an error due to null not being allowed in the primary key.

SQL Primary key at Table level
Whenever the primary key contains more than one column, it has to be specified at the table level.

Syntax
CREATE TABLE table_name
(
  field1 data_type,
  field2 data_type,
  ...
  PRIMARY KEY (field1)
)

Example
CREATE TABLE Employee
(
  Id INT NOT NULL,
  [Name] VARCHAR(50) NOT NULL,
  City VARCHAR(20) NOT NULL,
  PRIMARY KEY (Id)
)

Primary Key with Multiple Columns
If you want to add a primary key to more than one column, then that is not possible at the column level; that is possible at the table level.
CREATE TABLE Employee
(
  Id INT NOT NULL,
  [Name] VARCHAR(50) NOT NULL,
  City VARCHAR(20) NOT NULL,
  PRIMARY KEY (Id, [Name])
)

Primary Key with Alter Table
The primary key is typically defined at the time the table is created, but occasionally it might not be created in the table that already exists. However, we can use the Alter Statement to add the primary key.

For a Single Column
Syntax
ALTER TABLE Table_name
ADD PRIMARY KEY (column1);

Example
ALTER TABLE Employee
ADD PRIMARY KEY (Id);

For Multiple Columns
Syntax
ALTER TABLE Table_name
ADD CONSTRAINT primary_key_name PRIMARY KEY (column1, column2);

Example
ALTER TABLE Employee
ADD CONSTRAINT Employee_PK PRIMARY KEY (Id, [Name]);

Remove Primary Key
We can remove the primary key constraint from a table using the DROP statement.

Syntax
ALTER TABLE table_name
DROP CONSTRAINT primary_key_name;

Example
ALTER TABLE Employee
DROP CONSTRAINT Employee_PK;

We learned the new technique and evolved together.
Happy coding!

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Do you make use of SQL Server? Do some teams or DBAs still manage deployments by hand? Are project or financial constraints preventing the incorporation of CI/CD tools? However, there's a chance to use more than one SQL script.

Overview
Running SQL scripts is a standard procedure in database management. But handling several SQL files might make the procedure tiresome and time-consuming. Batch scripts are one of the ways that SQL Server offers for executing SQL scripts. We will examine how to effectively use a batch script to run several SQL files in SQL Server in this article.

Understanding Batch Scripting
Batch scripting is a powerful tool for automating tasks in Windows environments. It allows users to execute a series of commands or scripts in a sequential manner. These scripts are saved with a .bat extension and can be run by simply double-clicking them or through the command line.

Pre-requisite for Batch File
    This script deploys all the .sql files present in a directory or sub-directories in an order.
    NO SPACE in .sql file name.
    NO SPACE in sub-directories.
    To execute .sql in order, add a numeric sequence as follows:
    createtable.sql
    insertdata.sql
    execstoredproc....etc.
    Specify the SERVERNAME, which is mandatory.
    DATABASENAME is optional (Commented-out). In case enabling add (-d%dbname%) after -E at line like (SQLCMD -S%SERVERNAME% -E -d%dbname% -b -i%%G >> :: :: %logfilepath%).
    Specify the SCRIPTLOCATION, which is mandatory.
    The execution log will be captured on the same SCRIPTLOCATION for successful execution and failure.

Steps to Follow

• Copy the below batch script and save it as "ExecuteSQLFiles.bat".
• Update SERVERNAME, SCRIPTLOCATION, and LOGLOCATION accordingly for your needs.

    :: Pre-requisites to follow

    :: This script deploys all the .sql files present in a directory or sub-directories in an order.
    :: NO SPACE in .sql file name.
    :: NO SPACE in sub-directories.
    :: To execute .sql in order add numeric sequence as follows: 1.createtable.sql,
    :: 2.insertdata.sql, 3.execstoredproc....etc.
    :: Specify the SERVERNAME which is mandatory
    :: DATABASENAME is optional (Commented-out). In case enabling add (-d%dbname%) after -E at line like
    :: (SQLCMD -S%SERVERNAME% -E -d%dbname% -b -i%%G >> :: :: %logfilepath%).
    :: Specify the SCRIPTLOCATION which is mandatory.
    :: The execution log will be captured on the same SCRIPTLOCATION for successful execution and failure.

    @echo off
    setlocal enabledelayedexpansion

    set SERVERNAME=LAPTOP-AOVLBDQ4
    ::set DATABASENAME=MyWork
    set SCRIPTLOCATION=C:\Peter\AutoDepSQLFiles\SQL\
    set LOGLOCATION=C:\Peter\AutoDepSQLFiles\Logs\
    set hr=%time:~0,2%

    if "%hr:~0,1%" equ " " set hr=0%hr:~1,1%
    set logfilepath= %LOGLOCATION%\ExecutionLog_%date:~-4,4%%date:~-10,2%%date:~-7,2%_%hr%%time:~3,2%%time:~6,2%.log
    set cmd='dir %SCRIPTLOCATION%\*.sql /b/s'

    FOR /f %%G IN (%cmd%) DO (
    echo ******PROCESSING %%G FILE******
    echo ******PROCESSING %%G FILE****** >> %logfilepath%
    SQLCMD -S%SERVERNAME% -E -b -i%%G >> %logfilepath%
    IF !ERRORLEVEL! NEQ 0 GOTO :OnError
    )
    GOTO :Success

    :OnError
    echo ERROR ERROR ERROR
    echo One\more script(s) failed to execute, terminating bath.
    echo Check output.log file for more details
    EXIT /b

    :Success
    echo ALL the scripts deployed successfully!!
    EXIT /b

Copy the below SQL scripts into separate files in respective folders.
--File Name 1.TableCreation.sql

USE MyWork
GO

CREATE TABLE dbo.Employee (Id INT IDENTITY(1,1), Emp_Name VARCHAR(100))

--File Name 2.InsertData.sql

USE MyWork
GO

INSERT dbo.Employee
SELECT 'Peter'
UNION
SELECT 'Scott'


--File Name 3.AlterTable.sql

USE MyWork
GO

ALTER TABLE dbo.Employee ADD Email VARCHAR(200)

--File Name 4.UpdateTable.sql

USE MyWork
GO

UPDATE dbo.Employee
SET Email = '[email protected]'
WHERE Emp_Name = 'Peter'

UPDATE dbo.Employee
SET Email = '[email protected]'
WHERE Emp_Name = 'Scott'

• Execute the bat file, and upon successful completion, a log file will be generated in the Log directory.
• All SQL scripts within the folder will have been executed.
• If there are any failures, refer to the execution log for details

Folder Structure
Batch File

SQL Files

Verify The Deployment
As a part of this process, we initiated by creating an Employee table with Id and Emp_Name columns in the first file. Subsequently, we inserted two rows in the second file, followed by altering a table to include an Email column in the third script. Finally, in the fourth script, we updated the employee records to include email addresses.

In SQL Server, batch scripting offers a practical means of running numerous SQL files simultaneously. Batch scripts facilitate database management operations, increase productivity, and guarantee consistency in deployment procedures by automating the execution process. Users can efficiently handle their SQL execution demands by creating and running batch scripts by following the instructions provided in this article.

HostForLIFE.eu SQL Server 2022 Hosting
HostForLIFE.eu is European Windows Hosting Provider which focuses on Windows Platform only. We deliver on-demand hosting solutions including Shared hosting, Reseller Hosting, Cloud Hosting, Dedicated Servers, and IT as a Service for companies of all sizes.