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Description

This error indicates that a JSON item within your data cannot be successfully converted or 'cast' into the specified target SQL data type. It typically occurs when a JSON value's intrinsic type (e.g., a string, number, boolean, or object) is incompatible with the SQL type you are attempting to cast it to, leading to a data conversion failure.

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Error Message

sql json item cannot be cast to target type

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Known Causes

3 known causes

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Mismatched Data Type Conversion

Attempting to cast a JSON value (e.g., a non-numeric string like 'abc') to an incompatible SQL data type (e.g., an INTEGER or DATE).

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Extracting Complex JSON as Scalar

Trying to cast a JSON object or array extracted from a `jsonb` or `json` column directly to a scalar SQL type (e.g., TEXT, INT), when the target type expects a single atomic value.

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Invalid JSON Value Format

The JSON string being cast to a specific SQL type (like TIMESTAMP or NUMERIC) does not adhere to the expected format for that SQL type.

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Solutions

3 solutions available

1. Explicitly Cast JSON Values to Target Data Type easy

Ensure that you are correctly casting JSON values to the expected data type during retrieval.

1

Identify the specific JSON field and the target data type you are trying to cast it to. Examine your SQL query where the error occurs.

2

Use PostgreSQL's JSON casting operators or functions to explicitly convert the JSON value to the desired type. Common target types include `text`, `integer`, `numeric`, `boolean`, `date`, `timestamp`, etc.

-- Example: Casting a JSON string to an integer
SELECT (your_json_column ->> 'your_field')::integer AS your_integer_field
FROM your_table;

-- Example: Casting a JSON string representing a boolean
SELECT (your_json_column ->> 'your_boolean_field')::boolean AS your_boolean_field
FROM your_table;

-- Example: Casting a JSON string to a timestamp
SELECT (your_json_column ->> 'your_timestamp_field')::timestamp AS your_timestamp_field
FROM your_table;

3

If the JSON field might be `null` or might not exist, consider using `COALESCE` or `NULLIF` to handle these cases gracefully, especially before casting.

-- Example: Handling potential nulls before casting to integer
SELECT COALESCE((your_json_column ->> 'your_field')::integer, 0) AS your_integer_field
FROM your_table;

2. Validate JSON Structure and Data Types medium

Verify that your JSON data conforms to the expected structure and that the data within the JSON fields are of the types you anticipate.

1

Inspect the actual JSON data stored in your PostgreSQL table. Use `SELECT your_json_column FROM your_table LIMIT 10;` to view sample data.

SELECT your_json_column FROM your_table LIMIT 10;

2

Manually examine the structure and values of the problematic JSON fields. Check if a field that you expect to be a number is actually a string, an object, an array, or `null`.

3

If the JSON data is inconsistent or incorrect, you may need to update the data. This can be done with `UPDATE` statements, or by reprocessing the source data that generated the JSON.

-- Example: Updating a JSON field if it's an unexpected type
UPDATE your_table
SET your_json_column = jsonb_set(your_json_column, '{your_field}', to_jsonb(CAST(your_json_column ->> 'your_field' AS integer)))
WHERE jsonb_typeof(your_json_column -> 'your_field') <> 'number';

-- Note: This example assumes your_field should be a number. Adjust 'your_field' and the target type accordingly.

4

Consider using PostgreSQL's JSON functions like `jsonb_typeof()` to dynamically check the type of a JSON element before attempting a cast.

-- Example: Select rows where 'your_field' is not a number
SELECT * FROM your_table WHERE jsonb_typeof(your_json_column -> 'your_field') <> 'number';

3. Use `jsonb` for Better Performance and Type Handling medium

Convert your JSON column to `jsonb` to leverage its improved performance and data integrity features.

1

If your column is of type `json`, consider converting it to `jsonb`. `jsonb` stores JSON in a decomposed binary format, which is faster for querying and indexing, and offers better type checking.

2

Add a new `jsonb` column and copy the data from the `json` column.

ALTER TABLE your_table ADD COLUMN your_jsonb_column jsonb;
UPDATE your_table SET your_jsonb_column = your_json_column::jsonb;
-- You can then drop the old json column after verification.

3

Alternatively, you can drop and recreate the column as `jsonb` (this will require recreating indexes and constraints).

ALTER TABLE your_table DROP COLUMN your_json_column;
ALTER TABLE your_table ADD COLUMN your_json_column jsonb;
UPDATE your_table SET your_json_column = your_json_column::jsonb;
-- Recreate indexes and constraints on your_json_column.

4

When querying a `jsonb` column, the `->>` operator still returns `text`. You will still need to cast to your target type, but `jsonb`'s internal representation can sometimes make these casts more robust.

SELECT (your_jsonb_column ->> 'your_field')::integer AS your_integer_field
FROM your_table;

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Related Errors

5 related errors

PostgreSQL Error 2203G: Invalid JSON Type Cast