PostgreSQL raises error 42P18 when it cannot infer a concrete data type for a placeholder, NULL, or unknown literal in a query.
indeterminate_datatype (PostgreSQL Error 42P18) occurs when the server cannot infer a data type for a placeholder, NULL, or unknown literal. Supply an explicit type by casting the value or declaring parameter types in PREPARE or the client driver to resolve the error.
indeterminate_datatype (PostgreSQL Error 42P18)
PostgreSQL raises error 42P18, condition name indeterminate_datatype, when the planner cannot infer a concrete data type for a placeholder or expression.
The message usually reads “could not determine data type of parameter $1” and stops execution before planning the query.
Fixing the problem quickly matters because untyped values break prepared statements, UNION sets, and dynamic SQL, halting application workflows.
Untyped positional parameters such as $1 in PREPARE, EXECUTE, or driver-side bindings trigger the error when no type information is supplied.
NULL constants without explicit casts appear as type unknown, so combining them with typed columns or set operations can fail.
Mixing unknown literals across UNION, CASE, or VALUES lists prevents the planner from choosing one data type for the result column.
Functions that return unknown or text when a specific type is required can also expose the indeterminate_datatype condition.
Declare parameter types in PREPARE statements or in the client driver so PostgreSQL knows each placeholder’s type.
Add explicit CASTs (value::type) to NULL or string literals inside SELECT, UNION, VALUES, or function arguments.
Ensure all branches of UNION or CASE return the same typed expression to eliminate ambiguity.
If dynamic SQL is generated, embed type casts or use parameterized queries with correct bindings.
Prepared statement without types: supply PREPARE get_user(int) AS SELECT * FROM users WHERE id = $1;
UNION of typed and untyped rows: cast untyped literals (SELECT 1::int UNION ALL SELECT 2);
INSERT NULL into typed column: use NULL::text or NULL::uuid to match the target column type.
Function returning unknown: rewrite function signature or add RETURN NULL::target_type to give the planner a hint.
Always declare parameter types in PREPARE or rely on strongly typed driver placeholders.
Cast every NULL literal and ambiguous string in production SQL or code generators.
Use static analysis or Galaxy’s AI linting to highlight untyped expressions before queries reach the database.
Add unit tests that execute representative queries with EXPLAIN to catch datatype inference issues early.
42804 datatype_mismatch - occurs when two explicitly typed expressions conflict; solved by matching types or casting.
42704 undefined_object - raised when referenced type or column does not exist; fix by correcting identifiers.
42883 undefined_function - appears when no function matches given argument types; solved by adding casts or creating the function.
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Binding parameters from an application without specifying their data types leaves PostgreSQL with unknown placeholders that trigger 42P18.
Writing SELECT NULL or inserting NULL into a polymorphic expression gives the planner no clue about the required type.
Combining numeric columns with string or unknown constants inside UNION or CASE prevents PostgreSQL from selecting a single output type.
User-defined functions that default to text or unknown for NULL returns can propagate indeterminate types to the caller.
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The placeholder $1 has no declared type, so the planner cannot decide how to process it. Declare the parameter as int, text, etc., or cast it.
No. Any query with unknown literals, such as NULL in UNION or VALUES, can raise indeterminate_datatype.
Simple casts are optimized away during planning, so they have negligible impact compared with the benefit of eliminating the error.
Galaxy’s SQL editor flags untyped parameters in real time and offers CAST completions, preventing indeterminate_datatype before execution.
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