Extracting Substrings in Oracle SQL: A Step-by-Step Guide

Learn how to split Oracle SQL strings based on specific criteria, using examples and code snippets for practical understanding.
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Extracting Substrings in Oracle SQL: A Step-by-Step Guide

In the realm of database querying, sometimes we run into situations where we need to manipulate strings in ways that aren’t immediately straightforward. This is particularly true when dealing with Oracle SQL and its handling of string functions. One common problem is extracting particular segments from strings based on another reference string. Let’s dive into how you can achieve this with an Oracle SQL query.

The Challenge

Imagine you have a table with two columns: COL1 and COL2. The data in these columns are formatted with values separated by colons (":"). Your goal is to extract all parts of COL1 that come after a specific value found in COL2.

Given the following example:

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You want your output to look like this, extracting the segments after the respective COL2 value:

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The Solution

To achieve this in Oracle SQL, we can utilize Common Table Expressions (CTEs) along with the SUBSTR and REGEXP_SUBSTR functions. Below is a step-by-step approach to constructing your SQL query.

Step 1: Sample Data Preparation

First, let’s create a CTE that mimics your table structure. You can substitute this part with your actual table:

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Here, we define a dataset with two rows that you will be querying against.

Step 2: Extracting the Desired Substring

Next, we need to extract the portion of COL1 that comes after the value found in COL2. Here’s how you can do that:

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INSTR function retrieves the position of COL2 within COL1.

LENGTH provides the length of the COL2 string to help us cut COL1 at the right point.

SUBSTR fetches the substring starting just after COL2.

Step 3: Splitting the Substring into Separate Columns

Finally, we will break down the extracted substring (let’s call it col) into separate columns using REGEXP_SUBSTR. This function is ideal when extracting words or segments from a string.

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REGEXP_SUBSTR with the pattern \w+ extracts every word found in the string, based on the specified occurrence number.

Full Query Code

Here’s the complete SQL query bundled together into one cohesive unit:

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Expected Output

Running this query will give you the desired output, with results split into separate columns as shown below:

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Conclusion

Extracting substrings from strings based on other reference columns in Oracle SQL can be effectively achieved through a combination of SQL functions and Common Table Expressions. This guide provided an organized approach, ensuring clarity every step of the way.
Now you can confidently tackle similar substring extraction challenges within your own SQL projects!