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Description

Error 42804, 'datatype mismatch', indicates an attempt to perform an operation with incompatible data types. This typically happens when assigning data of one type to a column expecting another, or when using operators or functions with arguments that cannot be implicitly converted.

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Error Message

datatype mismatch

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Known Causes

3 known causes

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Incorrect Data Type Assignment

Attempting to insert or update a value into a column where its data type does not match the column's defined type, e.g., inserting a string into an integer column.

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Mismatched Function or Operator Arguments

Providing arguments of incompatible data types to a function or operator that cannot implicitly convert them, e.g., passing a date to a function expecting a number.

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Failed Implicit Type Coercion

PostgreSQL failed to implicitly convert data types during comparisons, joins, or other operations, leading to an incompatibility.

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Solutions

3 solutions available

1. Explicitly Cast Data Types easy

Convert one of the operands to match the other's data type.

1

Identify the column or literal causing the datatype mismatch in your query. For example, if you are comparing an `integer` column with a `text` literal, you need to convert the `text` to an `integer` or vice-versa.

2

Use the `::` casting operator or the `CAST()` function to explicitly convert the data type. Choose the appropriate target data type based on your operation.

SELECT * FROM your_table WHERE integer_column = '123'::integer;
-- Or using CAST:
SELECT * FROM your_table WHERE integer_column = CAST('123' AS integer);

3

If the mismatch is due to a function returning an unexpected type, cast the result of the function.

SELECT * FROM your_table WHERE some_function(column_a) = 'expected_value'::varchar;

2. Correct Column Data Types medium

Alter the table schema to ensure columns have compatible data types.

1

Determine the intended data type for the columns involved in the operation. Consult your application's requirements or the expected values.

2

Use the `ALTER TABLE` statement to modify the data type of the problematic column. Be cautious, as this can involve data conversion and potential data loss if not handled correctly.

ALTER TABLE your_table ALTER COLUMN column_name TYPE new_data_type;
-- Example: Changing a text column to integer
ALTER TABLE your_table ALTER COLUMN string_number TYPE integer USING string_number::integer;

3

If the data in the column cannot be directly converted, you might need to clean or transform it before altering the type, or consider adding a new column with the correct type and migrating data.

3. Review Function and Operator Usage medium

Ensure functions and operators are applied to operands of compatible types.

1

Examine the SQL query or application code that is triggering the error. Pay close attention to any functions or operators being used.

2

Consult the PostgreSQL documentation for the specific function or operator. Understand the expected data types for its arguments.

https://www.postgresql.org/docs/current/functions.html
https://www.postgresql.org/docs/current/sql-operators.html

3

If a function is being used, verify that the data types of the columns or literals passed to it are compatible with its signature. If not, use explicit casting (Solution 1) on the arguments.

SELECT some_function(column_a::text, column_b::integer) FROM your_table;

4

For operators, ensure that both operands are of compatible types. For instance, the `+` operator might behave differently or not be supported between a `timestamp` and a `text`.

SELECT timestamp_column + interval_value FROM your_table; -- Valid
-- SELECT timestamp_column + 'some_text' FROM your_table; -- Likely invalid

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Related Errors

5 related errors

PostgreSQL Error 42804: Datatype Mismatch in Operations