Скачать или смотреть How to Insert Multiple Values in a Loop in PL/SQL Without Unique Constraint Violations

Discover the solution to avoid unique constraint violations when inserting multiple records in PL/SQL loops. Learn how to use max function for safe data insertion.
---
This video is based on the question https://stackoverflow.com/q/63742153/ asked by the user 'Ystalio Di Staniovich' ( https://stackoverflow.com/u/8996970/ ) and on the answer https://stackoverflow.com/a/63779426/ provided by the user 'Ystalio Di Staniovich' ( https://stackoverflow.com/u/8996970/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: multiple Insert values in a loop

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Insert Multiple Values in a Loop in PL/SQL Without Unique Constraint Violations

In the world of database programming, specifically when working with PL/SQL, you might find yourself in situations where you need to insert multiple rows into a table using values that are derived from another table. However, if you're not careful, you can run into frustrating errors such as unique constraint violations. In this guide, we'll walk through a specific problem—where inserting values in a loop leads to a unique constraint error—and how to resolve it effectively.

Understanding the Problem

Let's say you have two tables in your database: table1 and table2. Here's the scenario:

You want to loop through the entries in table1 (for which var2 = 2) and insert certain values into table2.

Each insertion includes a count of existing entries in table2 to ensure the col2 field (another column in table2) remains unique for each value of col1 from table1.

You'll quickly find out, however, that trying to perform these insertions directly, using something like the count of rows, could lead to errors due to existing entries.

The error message "unique constraint violated" indicates that you're attempting to insert a row with values that already exist in the table.

Analyzing the Initial Code

Here’s the initial loop that caused the issue:

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

What's Wrong Here?

Count Dynamic Values: By adding count_rows + 1, you're creating a situation where if the count already exists, the insert will fail because both col1 and col2 will have non-unique combinations.

Fetching Values from the Same Table: This can compound the issue by making it difficult to keep track of unique entries, especially if multiple entries have similar characteristics.

The Solution

To fix this issue, we need to adjust how we determine the value for col2 during our insertions. Instead of counting current entries which can conflict with existing records, we can use the max() function to establish a baseline that minimally increases from existing records.

Here’s the Revised Code:

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

Key Improvements:

Use of MAX instead of COUNT: By switching to MAX(col2), we are not only preventing duplicates but also ensuring that we are always inserting a unique value for col2.

Handle NULL Values Gracefully: The NVL(max_rows, 0) expression ensures that if there are no rows returned (i.e., it's the first insertion for that col1), we start counting from 0 to avoid any null-related issues.

Conclusion

Inserting multiple values in a loop can be challenging, especially in scenarios where unique constraints exist. By using the max() function instead of a count, you can avoid unique constraint violations and allow for smoother data handling in PL/SQL. Always remember, when working with existing data, leveraging aggregate functions can be the key to success.

If you’ve faced similar challenges or have additional tips, feel free to share in the comments!