Postgresql Regex Match by End of String

Introduction

In this post, we will explore how to use regular expressions (regex) in PostgreSQL to match strings that end with a specific pattern. We will also discuss some common pitfalls and edge cases that may arise when using regex in PostgreSQL.

Background

Regular expressions are a powerful tool for searching and manipulating text patterns. In PostgreSQL, we can use the ~ operator to perform regex matching on string columns. However, when it comes to matching strings that end with a specific pattern, things can get tricky.

The Problem

Let’s consider an example table called sample with two columns: id and identity. We have inserted some data into this table:

create table sample(id int, identity varchar(20));

insert into sample (id, identity) values (1,'9822');
insert into sample (id, identity) values (2,'129822');
insert into sample (id, identity) values (3,'ABCD9822');
insert into sample (id, identity) values (4,'1234');

select * from sample;

This will produce the following result:

We want to select all rows where the identity column ends with the string '0987'. However, simply using the regex pattern '^0987$' will not produce the desired result. This is because PostgreSQL uses a different syntax for regex patterns.

The Solution

In PostgreSQL, we need to use the following regex pattern: %s . The %s placeholder represents any string value. So, our pattern becomes:

select * from sample where identity ~ '%s' and length(identity) = 7;

This query will return all rows where the identity column ends with '0987'.

Note that we are also using the length() function to ensure that the matched string has exactly 7 characters. This is necessary because the %s placeholder does not guarantee a specific length.

Another important thing to note is that the regex pattern will match even if the input string starts with some characters and ends with '0987'. For example, it will also match the string '0987129822'.

Best Practices

Here are some best practices for using regex in PostgreSQL:

• Always use the %s placeholder when performing regex matching on a specific column.
• Use the length() function to ensure that the matched string has exactly the desired length.
• Be aware that the regex pattern may match even if the input string starts with some characters and ends with the specified pattern.

Common Pitfalls

When using regex in PostgreSQL, there are several common pitfalls to watch out for:

1. Using the Wrong Placeholder

The most common mistake is using the wrong placeholder when performing regex matching. As we discussed earlier, always use the %s placeholder when searching for a specific string pattern.

# Wrong usage
select * from sample where identity ~ '0987' and length(identity) = 7;

This will not produce the desired result because the ~ operator is used to perform regex matching on a regular column, not on a specific value.

# Correct usage
select * from sample where identity ~ '%s' and length(identity) = 7;

2. Ignoring Leading Characters

Another common mistake is ignoring leading characters when performing regex matching. As we discussed earlier, the %s placeholder does not guarantee a specific length.

# Incorrect usage
select * from sample where identity ~ '0987129822' and length(identity) = 7;

This will not produce the desired result because the matched string may start with some characters before '0987'.

# Correct usage
select * from sample where identity ~ '%s' and length(identity) = 7;

Conclusion

In this post, we explored how to use regular expressions in PostgreSQL to match strings that end with a specific pattern. We discussed several common pitfalls and edge cases that may arise when using regex in PostgreSQL. By following the best practices outlined above, you can avoid these common mistakes and ensure accurate results.

1. Using the correct placeholder

• Always use the %s placeholder when performing regex matching on a specific column.
• Avoid using regular strings with ~ operator to match strings.

# Wrong usage
select * from sample where identity ~ '0987';

# Correct usage
select * from sample where identity ~ '%s';

2. Ignoring leading characters

• Use the %s placeholder when performing regex matching on a specific column.
• Be aware that the matched string may start with some characters before the specified pattern.

# Wrong usage
select * from sample where identity ~ '0987129822';

# Correct usage
select * from sample where identity ~ '%s';

Last modified on 2024-11-16