Skip to main content

How to add column safely (if not exists) in MySql?

On production environment if we want to run a script to add a column in a table it is
better to add it safely, but in MySql there is no direct way to do this.
Here safely means, if this column already exists in table ignore it otherwise add this new column.

Check the below query to safely add column safely in mysql:

Let's say we've a table "TEST_TO_DELETE" and we want to safely add new column "MY_NEW_COLUMN"

-- Drop table if exists
DROP TABLE IF EXISTS TEST_TO_DELETE;

-- Create table
CREATE TABLE TEST_TO_DELETE 
(
   Id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
   FirstName VARCHAR(50)
);

-- Step1. check if column exists or not
SELECT COUNT(*) INTO @countOfColumn
FROM `INFORMATION_SCHEMA`.COLUMNS 
WHERE TABLE_SCHEMA = 'TEST' 
        AND TABLE_NAME = 'TEST_TO_DELETE' 
        AND COLUMN_NAME = 'MY_NEW_COLUMN';

-- Step2. if column exists then @countOfColumn > 0 and execute the query
--    in this case execute the query
SET @sqlQuery = IF(@countOfColumn <= 0, ' ALTER TABLE TEST_TO_DELETE ADD COLUMN MY_NEW_COLUMN BIT NOT NULL DEFAULT 0 ', ' SELECT 1 ; ');

-- Step3. prepare the statement to 
PREPARE prpStatementToExecute FROM @sqlQuery;

-- Step4. Execute the query
EXECUTE prpStatementToExecute;




Comments

Popular posts from this blog

How to install Zen-coding plugin

As a web-developer, irrespective of the technologies (java, c-sharp, python, php e.t.c.…), we used to write CSS code to make our web-pages looks good if not at least we’re involved in write html codes. What if there is some tool to whom you give some instruction and that tool generates a good, well formatted html tags for you. These kind of coding is possible and known as “ Zen coding ” and there are lots of plug-in available from different vendors. We’re going to  discuss the steps to install this “zen-coding” plugin for “visual studio, eclipse, sublime-text & notepad++ in next few lines. Follow the below steps to install "zen-coding" plugin based on your editor.  Steps to install zen-coding plugin for (visual studio, eclipse, sublime-text,notepad++) -- -- For Visual Studio 1. Go to "Tools" -> "Extensions and Updates" 2. It'll open the "Extensions and Updates windows"    Select online form Left hand menu items ent...

Azure SQL - Re-build index and update stats

Useful script to rebuild table indexes and update stats You can update the queries based on your requirement. To update the table stats --Query to update the table stats SELECT N'UPDATE STATISTICS ' + t.TABLE_SCHEMA + '.' + t.TABLE_NAME + ' ;' FROM INFORMATION_SCHEMA.tables AS t WHERE t.TABLE_TYPE = N'BASE table'; GO To re-build table indexes: --To rebuild table index DECLARE @myDatabaseName NVARCHAR(255) = N'your-database-name'; DECLARE @runningTableName NVARCHAR(255); DECLARE @cmd NVARCHAR(1000); DECLARE @name NVARCHAR(100)= 'your-database-name'; -- Populate the database cursor. DECLARE myDatabaseLevelCursor CURSOR READ_ONLY FOR SELECT @name; OPEN myDatabaseLevelCursor; FETCH NEXT FROM myDatabaseLevelCursor INTO @myDatabaseName; WHILE @@FETCH_STATUS = 0 BEGIN -- In this command we're declaring table level cursor SET @cmd = 'DECLARE myTableCursor CURSOR READ_ONLY FOR SELECT '...

EFCore - Scaffold-DbContext how to use

EFCore versions, we don't have GUI to manage the DB-entities & dbContext like we used to have with EF6 (or EF5/4 version). With EFCore we've the Scaffold-DbContext command which helps us to create entities & DB context from our DB-objects.  Let's see how to use Scaffold-DbContext: Assume we're connecting with SQL Server so after creating a sample project you'll have to install EFCore related libraries as mentioned below.  Install entity-framework-core for SQL Server, at this time 3.1.9 is the latest stable version   Microsoft.EntityFrameworkcore   Microsoft.EntityFrameworkCore.SqlServer  To use Scaffold-DbContext, following two NuGet packages are required Microsoft.EntityFrameworkCore.Tools  Microsoft.EntityFrameworkCore.Design Let's say we've two DB tables (e.g. dbo.Employees & dbo.Users )  Now let's see how to use Scaffold-DbContext to create c-...