PostgreSQL Error - 22038 singleton_sql_json_item_required Error Explained and Fixed

What is the singleton_sql_json_item_required error?

PostgreSQL raises SQLSTATE 22038 when a SQL-JSON path expression is evaluated in a context that demands exactly one JSON item but the path returns two or more items. The server cannot choose which value to keep, so it aborts the query.

The error appears in functions that enforce singleton semantics, such as jsonb_path_query_first, jsonb_path_query_scalar, JSON_TABLE strict mode, and RETURNING clauses that expect one scalar.

What Causes This Error?

Multiple matches in a JSON path cause the error.

For instance, the path $[*] over an array returns all elements, not one.

Strict mode (STRICT) inside JSON_TABLE or jsonpath enforces a single result. If the path is lax by default but you add strict, the engine now expects one item.

Type casting a JSON path result to TEXT, INT, or another scalar also triggers the error when several items are produced.

How to Fix PostgreSQL Error 22038

First, confirm how many items the path returns by running jsonb_path_query.

If more than one row appears, adjust the path.

Use an index ([0]) or a key name to target one element. Alternatively, replace singleton functions with their multi-item counterparts, such as jsonb_path_query instead of jsonb_path_query_first.

Common Scenarios and Solutions

Querying an array without limiting the index is the top culprit. Adding [0] or [last] resolves it.

When extracting a single object property, ensure the path references the property directly: $."price" not $.*.

Best Practices to Avoid This Error

Always test JSON paths with jsonb_path_query before casting.

Confirm you receive exactly one row.

Use Galaxy’s linting in the SQL editor. The AI copilot flags paths that could return multiple items and offers indexed alternatives.

Related Errors and Solutions

SQLSTATE 22039 json_sql_item_wrong_type fires when the returned item type is wrong. Narrow the path or cast properly.

SQLSTATE 2203B array_subscript_error occurs when array indexes are out of range. Validate indexes before querying.

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