migration script sql server for inserting an item - sql

Question

I am trying to create an Migration Script but i need some help:, i had the very basic script to insert an item into a table but i am trying to do it in a way to check for the item first if it exists, then insert it else skip it
here is my code:
use mydatabase;
INSERT INTO dbo.mytable(col1,col2,col3)
SELECT '3','test1','test3/abc.html';

Answer 1

You don't need to repeat the expression just use value construct like that :
INSERT INTO dbo.mytable(col1,col2,col3)
SELECT t.col1, t.col2, t.col3
FROM (values (3, 'test1','test3/abc.html')) t (col1, col2, col3)
WHERE NOT EXISTS (
SELECT 1
FROM dbo.mytable m
WHERE m.col1 = t.col1
AND m.col2 = t.col2
AND m.col3 = t.col3
);

Answer 2

INSERT INTO dbo.mytable(col1,col2,col3)
SELECT '3','test1','test3/abc.html'
WHERE NOT EXISTS (
SELECT 1
FROM dbo.mytable
WHERE col1='3'
AND col2='test1'
AND col3='test3/abc.html'
)
You can change the where depending on what you consider already inserted.

Answer 3

Something like this (but you would need some kind of key to identify if the record exists or not) -
IF NOT EXISTS(SELECT 1 FROM dbo.mytable WHERE col1 = '3' AND col2 = 'test1' AND col3 = 'test3/abc.html')
BEGIN
insert into dbo.mytable(col1,col2,col3)
SELECT '3','test1','test3/abc.html'
END

Answer 4

Use a MERGE:
CREATE TABLE #mytable (col1 nvarchar(20), col2 nvarchar(20), col3 nvarchar(20))
INSERT INTO #mytable(col1,col2,col3)
SELECT '3','test1','test3/abc.html';
Merge #mytable t
USING (SELECT '3','test1','test3/abc.html') s (col1, col2, col3)
ON t.col1 = s.col1
AND t.col2 = s.col2
AND t.col3 = s.col3
when not matched by target then
INSERT (col1,col2,col3) VALUES (s.col1, s.col2, s.col3);