How to Fix the SQL Error: syntax error at or near 'int' in PostgreSQL

A comprehensive guide on resolving syntax errors in PostgreSQL when inserting data using foreign keys, especially for handling `serial` columns.
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Troubleshooting SQL Error: Syntax Error at or Near "int"

When working with SQL databases like PostgreSQL, you might occasionally encounter perplexing errors that stem from syntax issues. One common issue arises when attempting to insert data into tables that reference foreign keys. In this post, we will address a specific error: ERROR: syntax error at or near "int".

The Problem

You've created two tables: Countries and Cities. The Countries table has a serial column for the primary key, while the Cities table references this primary key as a foreign key. However, when trying to execute an insert command, you're met with a syntax error that appears related to how you're trying to obtain and use the id from the Countries table.

Here’s a snippet of the problematic insert statement:

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

This is not the correct syntax for retrieving values in PostgreSQL, and it leads to confusion and a resultant error.

Understanding the Solution

To clear up this issue, it is important to understand how serial columns and sequences work in PostgreSQL. A serial column is essentially an auto-incrementing number that uses sequences in the background. To get the last generated value of a serial column, PostgreSQL provides the currval function, but you need a proper way of identifying the sequence associated with the serial column.

Step-by-Step Solution

Insert Data into Countries: First, you correctly insert a new country description into the Countries table.

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

Retrieve the Last Inserted ID: To insert into the Cities table using the ID from the Countries table, use the currval() function along with pg_get_serial_sequence() to fetch the last generated ID.

Here’s how you should write the insertion into the Cities table:

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

Explanation of the Solution

currval(): This function returns the most recent value generated by a sequence for the current session.

pg_get_serial_sequence('countries', 'id'): This function helps you get the exact sequence name associated with the id column of the Countries table.

Key Benefits

Session Safety: The currval function is session-specific, meaning even if multiple users are inserting countries concurrently, your session will still return the appropriate last ID from your insert.

Conclusion

By properly modifying how you retrieve the last inserted ID from the Countries table and correcting the syntax of your SQL statement, you can successfully insert data into your Cities table without running into syntax errors. This approach simplifies your operations and helps maintain integrity across your tables, especially when dealing with foreign keys.

Now you have a clearer understanding of how to handle such SQL problems in PostgreSQL. Happy coding!