Trimming Special Characters from Data: A Step-by-Step Guide for Oracle SQL

Trimming and Concatenating Data with Special Characters

As a data analyst or programmer, working with data that contains special characters can be challenging. In this article, we will explore how to trim data after special characters and concatenate row data into columns with a comma delimiter.

Understanding the Current Data Format

The current data format is as follows:

INDIA-001 UNIT1-RUNNING
AUSTRIA-002 UNIT2-RUNNING
CHINA-003 UNIT1-RUNNING
JAPAN-004 UNIT2-ONHOLD.,

As we can see, each row contains a country code, a unit number, and an activity status. The country code is followed by a hyphen, a unit number, and then the activity status. There is also a special character in the last row, which is a comma (,) at the end of the string.

Understanding the Expected Output

The expected output should be as follows:

INDIA,AUSTRIA,CHINA,JAPAN

As we can see, each country code has been extracted and separated from the rest of the data.

Using LISTAGG() with Substring Operations

To achieve this, we can use the LISTAGG() function in Oracle SQL, along with some substring operations. The basic idea is to extract the country code from each row by finding the position of the hyphen and then taking a substring from the beginning of the string up to that point.

Here’s an example query:

SELECT LISTAGG(SUBSTR(data, 1, INSTR(data, '-') - 1), ',')
       WITHIN GROUP (ORDER BY TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3))) countries
FROM yourTable;

Let’s break down this query:

SUBSTR(data, 1, INSTR(data, '-') - 1) extracts the country code from each row. The INSTR() function returns the position of the hyphen in the string. By subtracting 1 from this value, we get the length of the country code.
SUBSTR(data, INSTR(data, '-') + 1, 3) extracts the unit number and activity status from each row. We take a substring starting from the position after the hyphen to the third character (since there are three characters in total).
TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3)) converts the unit number and activity status to numbers so that we can order them correctly.
The ORDER BY clause sorts the rows based on the converted unit number and activity status.
The WITHIN GROUP clause groups the results by country code.
Finally, the LISTAGG() function concatenates the country codes into a single string separated by commas.

Understanding How the Query Works

Let’s use an example to illustrate how this query works. Suppose we have the following data:

INDIA-001 UNIT1-RUNNING
AUSTRIA-002 UNIT2-RUNNING
CHINA-003 UNIT1-RUNNING
JAPAN-004 UNIT2-ONHOLD,

Here’s how the query would process this data:

For the first row (INDIA-001 UNIT1-RUNNING), SUBSTR(data, 1, INSTR(data, '-') - 1) returns "INDIA", and TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3)) returns 001. The row is then sorted based on this value.
For the second row (AUSTRIA-002 UNIT2-RUNNING), SUBSTR(data, 1, INSTR(data, '-') - 1) returns "AUSTRIA", and TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3)) returns 002. The row is then sorted based on this value.
For the third row (CHINA-003 UNIT1-RUNNING), SUBSTR(data, 1, INSTR(data, '-') - 1) returns "CHINA", and TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3)) returns 003. The row is then sorted based on this value.
For the fourth row (JAPAN-004 UNIT2-ONHOLD,), SUBSTR(data, 1, INSTR(data, '-') - 1) returns "JAPAN", and TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3)) returns 004. However, this row contains a comma at the end of the string, which is not handled by the query. To fix this, we need to add some extra logic to remove the comma.

Handling Extra Logic: Removing Comma

To handle rows that contain commas at the end of the string, we can use a combination of REGEXP_REPLACE() and SUBSTR(). The basic idea is to extract the country code from the row using REGEXP_REPLACE(), which replaces special characters with an empty string. We can then use SUBSTR() to extract the unit number and activity status.

Here’s an example query:

SELECT LISTAGG(
  SUBSTR REGEXP_REPLACE(data, '[^A-Z0-9_-]+', ''), 
  ',')
WITHIN GROUP (ORDER BY TO_NUMBER(SUBSTR(data, INSTR(data, '-') + 1, 3))) countries
FROM yourTable;

In this query, REGEXP_REPLACE() replaces all characters that are not letters, numbers, underscores, or hyphens with an empty string. This effectively removes the comma from the end of the string.

Conclusion

Trimming data after special characters and concatenating row data into columns with a comma delimiter is a common task in data analysis and programming. By using LISTAGG() along with substring operations, we can extract the country code from each row and sort them correctly. However, handling rows that contain commas at the end of the string requires some extra logic. With these techniques, you should be able to trim and concatenate your data effectively.

Last modified on 2024-11-27