Adding Column If It Does Not Exist

MySQL: ALTER TABLE if column not exists

Use the following in a stored procedure:

IF NOT EXISTS( SELECT NULL
            FROM INFORMATION_SCHEMA.COLUMNS
           WHERE table_name = 'tablename'
             AND table_schema = 'db_name'
             AND column_name = 'columnname')  THEN

  ALTER TABLE `TableName` ADD `ColumnName` int(1) NOT NULL default '0';

END IF;

Add a column to a table, if it does not already exist

You can use a similar construct by using the sys.columns table io sys.objects.

IF NOT EXISTS (
  SELECT * 
  FROM   sys.columns 
  WHERE  object_id = OBJECT_ID(N'[dbo].[Person]') 
         AND name = 'ColumnName'
)

Adding column if it does not exist

Another option that does not require creating a helper function (or an already complete data.frame) using tibble's add_column:

library(tibble)

cols <- c(top_speed = NA_real_, nhj = NA_real_, mpg = NA_real_)

add_column(mtcars, !!!cols[setdiff(names(cols), names(mtcars))])

add column to mysql table if it does not exist

Note that INFORMATION_SCHEMA isn't supported in MySQL prior to 5.0. Nor are stored procedures supported prior to 5.0, so if you need to support MySQL 4.1, this solution isn't good.

One solution used by frameworks that use database migrations is to record in your database a revision number for the schema. Just a table with a single column and single row, with an integer indicating which revision is current in effect. When you update the schema, increment the number.

Another solution would be to just try the ALTER TABLE ADD COLUMN command. It should throw an error if the column already exists.

ERROR 1060 (42S21): Duplicate column name 'newcolumnname'

Catch the error and disregard it in your upgrade script.

Insert column if it doesn't exist

Try this:

IF (SELECT COUNT(*) FROM syscolumns WHERE name = 'HasAccess24_7'
AND OBJECT_NAME(object_id) = 'tSafeUnit') = 0
BEGIN
    ALTER TABLE dbo.tSafeUnit ADD HasAccess24_7 tinyint not null default 0
END

When using a pandas dataframe, how do I add column if does not exist?

You check it like this:

if 'Met' not in df:
    df['Met'] = df['freqC'] * df['coverage'] 

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