add column for a table if this column not exists using T-SQL in SQLServer
IF NOT EXISTS (SELECT * FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'LandlordInfo' AND COLUMN_NAME = 'IsSigned')
BEGIN
ALTER TABLE LandlordInfo ADD IsSigned bit null
END
WHERE TABLE_NAME = 'LandlordInfo' AND COLUMN_NAME = 'IsSigned')
BEGIN
ALTER TABLE LandlordInfo ADD IsSigned bit null
END