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How to Efficiently Avoid Duplicates When Using INSERT INTO SELECT in SQL Server?
How to Efficiently Avoid Duplicates When Using INSERT INTO SELECT in SQL Server?
Jan 13, 2025 am 11:21 AM
The INSERT INTO SELECT statement in SQL Server efficiently avoids duplicate data
In database operations, inserting data from one table to another while avoiding duplication is a common task. This article discusses how to efficiently add records in Table1 to Table2 to avoid ID duplication.
One way is to use the IF-ELSE statement to check whether the ID exists in Table2 before inserting:
IF NOT EXISTS(SELECT 1 FROM Table2 WHERE Id=1) INSERT INTO Table2 (Id, name) SELECT Id, name FROM Table1 ELSE INSERT INTO Table2 (Id, name) SELECT Id, name FROM Table1 WHERE Table1.Id1
However, this method requires writing multiple INSERT INTO-SELECT statements based on conditions. In search of a more efficient solution, we explore three alternatives:
1. Use NOT EXISTS
INSERT INTO TABLE_2
(id, name)
SELECT t1.id,
t1.name
FROM TABLE_1 t1
WHERE NOT EXISTS(SELECT id
FROM TABLE_2 t2
WHERE t2.id = t1.id)
2. Use NOT IN
INSERT INTO TABLE_2
(id, name)
SELECT t1.id,
t1.name
FROM TABLE_1 t1
WHERE t1.id NOT IN (SELECT id
FROM TABLE_2)
3. Use LEFT JOIN/IS NULL
INSERT INTO TABLE_2
(id, name)
SELECT t1.id,
t1.name
FROM TABLE_1 t1
LEFT JOIN TABLE_2 t2 ON t2.id = t1.id
WHERE t2.id IS NULL
Among these three methods, the LEFT JOIN/IS NULL method is less efficient than the other methods. For inserting data in SQL Server's INSERT INTO SELECT query while avoiding duplication, NOT EXISTS and NOT IN techniques provide the best performance.
The above is the detailed content of How to Efficiently Avoid Duplicates When Using INSERT INTO SELECT in SQL Server?. For more information, please follow other related articles on the PHP Chinese website!
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