Ошибка case types character varying and integer cannot be matched

Introduction

The error message «ERROR: CASE types character varying and numeric cannot be matched» is encountered when you are using the CASE statement in a SQL query, and you are trying to compare a character data type (such as character varying or text) to a numeric data type (such as integer or decimal).

Here is an example of a query that would trigger this error:

SELECT 
 *
FROM users
WHERE
 CASE
 WHEN age < 18 THEN 'minor'
 ELSE 'adult'
 END = 'minor';

In this example, the age column is a numeric data type, but the 'minor' and 'adult' values being compared to it are character data types.

To fix this error, you will need to ensure that the data types being compared in the CASE statement are compatible. There are a few different ways you can do this, depending on your specific needs:

Method 1: Cast the Numeric Value to a Character Data Type

One way to fix the error is to explicitly convert the numeric value to a character data type using a type casting function such as ::text or ::varchar. For example:

SELECT 
 *
FROM users
WHERE
 CASE
 WHEN age::text < '18' THEN 'minor'
 ELSE 'adult'
 END = 'minor';

In this revised query, the age column is explicitly converted to a text data type using the ::text type casting function. This allows the CASE statement to compare the age column to the character data type 'minor' without generating an error.

Method 2: Use Numeric Values Instead of Character Values in the CASE Statement

Another way to fix the error is to use numeric values instead of character values in the CASE statement. For example:

SELECT 
 *
FROM users
WHERE
 CASE
 WHEN age < 18 THEN 1
 ELSE 2
 END = 1;

In this revised query, the CASE statement compares the age column to the numeric values 1 and 2 instead of the character values 'minor' and 'adult'. This allows the query to be executed without generating an error.

Method 3: Use a Different Comparison Operator

In some cases, you may be able to fix the error by using a different comparison operator in the CASE statement. For example, instead of using the < operator, you could use the ILIKE operator, which performs a case-insensitive match on character data types:

SELECT 
 *
FROM users
WHERE
 CASE
 WHEN age::text ILIKE '%18%' THEN 'minor'
 ELSE 'adult'
 END = 'minor';

In this revised query, the age column is explicitly converted to a text data type using the ::text type casting function. The ILIKE operator is then used to perform a case-insensitive match on the age column and the character value '18'. This allows the CASE statement to be executed without generating an error.

Here are a few more examples to illustrate how you can use the methods I described above to fix the «ERROR: CASE types character varying and numeric cannot be matched» error:

Example 1: Using Method 1 (Casting the Numeric Value)

Suppose we have a table called products with the following structure:

We want to retrieve all the products that have a price less than 10 and belong to the 'clothes' category. Here’s how we can do that using the CASE statement:

SELECT 
 *
FROM products
WHERE
 category = 'clothes' AND 
 CASE
 WHEN price::text < '10' THEN 'cheap'
 ELSE 'expensive'
 END = 'cheap';

In this query, the price column is explicitly converted to a text data type using the ::text type casting function. This allows the CASE statement to compare the price column to the character value '10' without generating an error.

The query would return the following rows:

Example 2: Using Method 2 (Using Numeric Values)

Suppose we have a table called customers with the following structure:

We want to retrieve all the customers who have more than 100 loyalty points. Here’s how we can do that using the CASE statement:

SELECT 
 *
FROM customers
WHERE
 CASE
 WHEN loyalty_points > 100 THEN 1
 ELSE 0
 END = 1;

In this query, the CASE statement compares the loyalty_points column to the numeric values 1 and 0 instead of character values. This allows the query to be executed without generating an error.

The query would return the following rows:

Example 3: Using Method 3 (Using a Different Comparison Operator)

Suppose we have a table called employees with the following structure:

Conclusion

To conclude, the «ERROR: CASE types character varying and numeric cannot be matched» error is encountered when you are using the CASE statement in a SQL query and you are trying to compare a character data type to a numeric data type. To fix this error, you can use one of the following methods:

1. Cast the numeric value to a character data type using a type casting function such as ::text or ::varchar.
2. Use numeric values instead of character values in the CASE statement.
3. Use a different comparison operator that is compatible with both the numeric and character data types.

I hope this helps! Let me know if you have any questions or need further clarification on any of the concepts I discussed.