PostgreSQL raises 2200G when it cannot resolve a common data type for polymorphic or variadic function arguments.
PostgreSQL Error 2200G (most_specific_type_mismatch) occurs when the server fails to find a single data type that safely represents all arguments in a polymorphic or variadic function call. Cast all arguments to a shared, explicit type or use type-specific function variants to resolve the conflict.
PostgreSQL Error 2200G
Error 2200G appears when PostgreSQL cannot infer a single data type for all arguments supplied to a polymorphic, variadic, or set operation such as UNION, GREATEST, or LEAST. The planner needs one “most specific” type to guarantee safe evaluation.
The condition name most_specific_type_mismatch signals that automatic type promotion failed.
Until you manually align types, PostgreSQL refuses to execute the query to avoid unintended data loss or incorrect comparison results.
Leaving this error unresolved blocks query execution, breaks application workflows, and masks deeper data-model pitfalls.
Addressing it early improves query reliability, prevents silent truncation, and keeps polymorphic functions predictable across environments.
Type conflicts surface most often in calls to GREATEST/LEAST, COALESCE, array functions, UNION statements, and custom PL/pgSQL functions defined with ANYELEMENT or ANYARRAY parameters.
When literals or columns differ in type (for example integer vs text), PostgreSQL cannot choose a common supertype.
Conflicts also occur when mixing unknown string literals with numeric types, passing NULL without casting, or supplying domain types alongside base types. The issue is version-agnostic but shows up frequently from PostgreSQL 9.6 through 16.
Force a shared type by casting every argument explicitly: SELECT GREATEST(1::numeric, '2'::numeric).
Alternatively, call a type-specific variant such as GREATEST(int, int) only. Adjust polymorphic function signatures to concrete types, or add USING clauses to UNION queries.
For application code, sanitize inputs before building dynamic SQL. Galaxy’s editor catches mismatched literals early with inline type hints, and its AI copilot suggests the correct CAST syntax automatically.
Scenario: UNION different column types. Solution: CAST columns in each SELECT to one datatype. Scenario: Variadic text functions with NULL.
Solution: CAST NULL to text. Scenario: ANYARRAY function mixing int[] and numeric[]. Solution: Convert one array.
Use explicit casts in production queries, store literals in bind parameters with the correct type, and enable statement linting in your CI pipeline.
Galaxy’s semantic layer can enforce endorsed query versions that already contain explicit casts.
Similar issues include SQLSTATE 42804 (datatype_mismatch) for assignment mismatches, 2200H (sequence_generator_limit_exceeded) for sequence bounds, and 42883 (undefined_function) when polymorphic resolution fails entirely. They share root causes but differ in context; each has unique fixes.
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Mixing numeric and text literals (e.g., 1 vs '2') inside GREATEST, LEAST, or UNION prevents PostgreSQL from selecting one type.
NULL and '' default to type unknown.
Without explicit casts, polymorphic resolution stops because unknown cannot dominate concrete types.
Passing int[] and numeric[] to ANYARRAY functions leaves no single array element type, triggering error 2200G.
Using domain types alongside their base types in UNION queries can confuse the type chooser, producing a mismatch.
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No. The engine blocks the query before execution, so underlying data remains safe.
PostgreSQL does not offer a flag to skip type resolution. You must correct the query.
A CAST provides the planner a definitive type, removing ambiguity and allowing evaluation.
Galaxy’s AI copilot flags mismatched literals in real time and suggests explicit casts, reducing runtime failures.
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