Скачать или смотреть How to Insert Data Based on Conditions from One Table to Another in SQL

Learn how to efficiently transfer data between tables in SQL based on specific conditions, enhancing your data management skills with practical examples.
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Efficiently Transferring Data Between Tables in SQL

In database management, there often arises a need to move or copy data from one table to another based on specific conditions. This can be especially useful when you're dealing with different schemas or when the destination table has more fields that depend on certain values from the source table. In this guide, we will explore how to insert data from one table into another table based on a column condition using SQL Server.

The Problem Statement

Suppose you have two tables: TableA and TableB. Here's a quick look at their structure:

TableA

IDNameOption1FirstAdd into box2SecondDon't Add3ThirdAdd into boxTableB

IDNameOptionStatus1FirstAdd into boxApproved2SecondDon't AddReject3ThirdAdd into boxApprovedIn this scenario, you need to insert data from TableA into TableB, but with the requirement that the Status column in TableB depends on the value of the Option column in TableA. Here’s the rule:

If the Option value is "Add into box", the corresponding Status in TableB should be "Approved".

For any other value, it should be "Rejected".

The Solution

To achieve this, we can use an INSERT INTO ... SELECT statement combined with a CASE expression to handle the conditional logic for the Status column. Below is the SQL query that accomplishes this task:

[[See Video to Reveal this Text or Code Snippet]]

Breaking Down the Query

1. INSERT INTO TableB (Id, Name, Option, Status)

This part of the query specifies the target table (TableB) and the columns into which we will insert the data.

2. SELECT Id, Name, Option

Here, we select the Id, Name, and Option columns from TableA, which will directly correspond to the same columns in TableB.

3. CASE Statement

The CASE expression is pivotal in this query:

It evaluates the Option column from TableA.

If the option is "Add into box", it assigns the value "Approved" to the Status column in TableB.

If it's any other value, it assigns "Rejected".

4. FROM TableA

Finally, we specify that the data is coming from TableA.

Advantages of This Approach

Simple and Clear: Using a single SQL command simplifies the data transfer process while ensuring clarity in what data is being manipulated.

Flexible: The CASE statement allows for complex conditions, which can be adjusted as per your requirements.

Conclusion

Transferring data between tables based on conditions can seem daunting at first, but as we've seen, it can be efficiently done using SQL commands with conditional logic. This approach ensures your data remains organized and in line with the conditions set based on your business rules.

Feel free to experiment with the provided SQL query in your own environment to understand how it works. Happy querying!