PostgreSQL raises 42P08 (ambiguous_parameter) when it cannot infer a single data type for an untyped literal or parameter.
ambiguous_parameter (PostgreSQL 42P08) means the query contains an untyped literal or parameter whose data type could match multiple columns or operators. Add an explicit CAST or type hint (::datatype) to remove the ambiguity and rerun the statement.
ambiguous_parameter
PostgreSQL throws 42P08 when it meets a parameter or untyped literal that can map to more than one data type. The planner needs a single type to choose operators and indexes. If it cannot decide, it aborts with ambiguous_parameter.
The error appears most in prepared statements, UNION queries, and functions where a placeholder value is compared against columns of different types.
Fixing it is critical because PostgreSQL will not run the query until each parameter has one clear type.
Using the same positional parameter (for example, $1) in expressions that reference columns with different data types confuses the planner.
It sees one parameter but several possible types.
Supplying an untyped string literal like '' or NULL without a CAST inside a UNION or CASE expression forces PostgreSQL to guess the target type, often resulting in ambiguity.
Add an explicit CAST such as $1::integer or CAST(NULL AS text) so the planner instantly knows the intended type.
Rewrite the query so each occurrence of a given parameter is compared only with columns of the same type, or use multiple parameters ($1, $2) with explicit casts.
Prepared statements that reuse one placeholder across numeric and text columns must separate the parameters or cast them.
UNION queries that return NULL for missing columns should cast the NULL to the correct column type.
Stored procedures that concatenate JSON and text may need CAST($1 AS jsonb) or TEXT depending on the expected argument.
Always cast untyped literals and NULLs in UNIONs, CASE, and COALESCE.
Align parameter types with column types when building dynamic SQL.
Enable strict code review or use Galaxy's linting to highlight uncast literals before execution.
Error 42804 datatype_mismatch occurs when the cast is wrong rather than missing. Error 42883 undefined_function appears if PostgreSQL selects the wrong operator due to ambiguous types. Both are solved with explicit casts and correct operator choice.
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$1 compared to an integer column in one place and a text column in another leaves PostgreSQL unable to choose a type.
SELECT NULL in one branch and SELECT text in another forces an ambiguous result unless the NULL is cast.
Empty strings inherit no type.
When used in mixed-type expressions they trigger 42P08.
Functions like COALESCE(NULL, column) can fail unless the NULL is cast to the column's data type.
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No. The error only reflects a query that lacks clear type information. Your data remains safe.
No. PostgreSQL must know each parameter's type. Suppressing the error would risk wrong results and index misuse.
NULL has no inherent data type. Casting it lets PostgreSQL pick the correct operators and plan.
Galaxy's AI copilot inserts type casts automatically and its linter warns about untyped literals before you run the query.
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