SQL alter script - copying from one table to another - sql

Question

I'm trying to figure out how to implement the alter script described below. I'm familiar with the basics if insert/select already, but this is a lot more complex.
I have a legacy table and need to move its data to a new table with more columns. The new table has already been made public to some select users, who may have already manually moved the common data over.
So for each row in LegacyTable:
see if it already exists in NewImprovedTable (by checking for a match on a string field that exists in both tables)
if not, copy its over to NewImprovedTable
regardless of whether it had been copied to NewImprovedTable automatically just now, or previously by the user...
auto-populate a new Name field in NewImprovedTable (must be unique - e.g. "Legacy1", "Legacy2", etc.)
set an IsLegacy flag in NewImprovedTable
I need to implement this in both MS SQL and Oracle, but once I work out the logic on one I can figure out the syntax on the other.

Answer 1

The solution I settled on (in SQL Server - still need to port to Oracle):
IF NOT EXISTS(SELECT 1
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'NewImprovedTable'
AND COLUMN_NAME = 'legacyFlg')
BEGIN
ALTER TABLE [NewImprovedTable]
ADD legacyFlg TINYINT NULL
ALTER TABLE [LegacyTable]
ADD improvedId INT NULL
END
GO
IF NOT EXISTS(SELECT 1 FROM ImprovedTable WHERE legacyFlg = 1)
BEGIN
MERGE ImprovedTable AS TARGET
USING LegacyTable AS SOURCE
ON (TARGET.stringField = SOURCE.stringField)
WHEN NOT MATCHED THEN
INSERT (name, <other columns>, legacyFlg)
VALUES('Legacy' + SOURCE.stringField, <other column values>, 1)
WHEN MATCHED THEN
UPDATE SET TARGET.legacyFlg = 1;
END
GO
IF NOT EXISTS(SELECT 1 FROM LegacyTable WHERE improvedId <> 0)
BEGIN
MERGE LegacyTable AS TARGET
USING NewImprovedTable AS SOURCE
ON (SOURCE.stringField = TARGET.stringField)
WHEN MATCHED THEN
UPDATE SET TARGET.improvedId = SOURCE.pId;
END
GO

Answer 2

You could try using this, where 'input' is the string you are trying to confirm if already exists:
SELECT * FROM`NewImprovedTable` WHERE `Variable`='input'
This will return the whole row if found any match, if not it will return null, you can play with that
As for the unique ID field you need to create a primary key on your table with the auto increment option enable, for example
CREATE TABLE Persons
(
P_Id INT NOT NULL AUTO_INCREMENT,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
PRIMARY KEY (P_Id)
)
In this last example P_Id is set as an autoincrement variable, each time you crate a new row it will auto fill this column with a unique number.
You should check this page
http://www.w3schools.com/sql/sql_primarykey.asp