Conversion rules in Google Standard SQL

Conversion includes, but is not limited to, casting, coercion, and supertyping.

  • Casting is explicit conversion and uses the CAST() function.
  • Coercion is implicit conversion, which Google Standard SQL performs automatically under the conditions described below.
  • A supertype is a common type to which two or more expressions can be coerced.

There are also conversions that have their own function names, such as PARSE_DATE(). To learn more about these functions, see Conversion functions

Comparison of casting and coercion

The following table summarizes all possible cast and coercion possibilities for Google Standard SQL data types. The Coerce to column applies to all expressions of a given data type, (for example, a column).

From type Cast to Coerce to
INT64 BOOL
INT64
NUMERIC
FLOAT64
STRING
NUMERIC
FLOAT64
NUMERIC INT64
NUMERIC
FLOAT64
STRING
FLOAT64
FLOAT64 INT64
NUMERIC
FLOAT64
STRING
 
BOOL BOOL
INT64
STRING
 
STRING BOOL
INT64
NUMERIC
FLOAT64
STRING
BYTES
DATE
TIMESTAMP
 
BYTES STRING
BYTES
 
DATE STRING
DATE
TIMESTAMP
TIMESTAMP STRING
DATE
TIMESTAMP
 
ARRAY ARRAY  
STRUCT STRUCT  

Casting

Most data types can be cast from one type to another with the CAST function. When using CAST, a query can fail if Google Standard SQL is unable to perform the cast. If you want to protect your queries from these types of errors, you can use SAFE_CAST. To learn more about the rules for CAST, SAFE_CAST and other casting functions, see Conversion functions.

Coercion

Google Standard SQL coerces the result type of an argument expression to another type if needed to match function signatures. For example, if function func() is defined to take a single argument of type FLOAT64 and an expression is used as an argument that has a result type of INT64, then the result of the expression will be coerced to FLOAT64 type before func() is computed.

Supertypes

A supertype is a common type to which two or more expressions can be coerced. Supertypes are used with set operations such as UNION ALL and expressions such as CASE that expect multiple arguments with matching types. Each type has one or more supertypes, including itself, which defines its set of supertypes.

Input type Supertypes
BOOL BOOL
INT64 INT64
FLOAT64
NUMERIC
FLOAT64 FLOAT64
NUMERIC NUMERIC
FLOAT64
STRING STRING
DATE DATE
TIMESTAMP TIMESTAMP
BYTES BYTES
STRUCT STRUCT with the same field position types.
ARRAY ARRAY with the same element types.

If you want to find the supertype for a set of input types, first determine the intersection of the set of supertypes for each input type. If that set is empty then the input types have no common supertype. If that set is non-empty, then the common supertype is generally the most specific type in that set. Generally, the most specific type is the type with the most restrictive domain.

Examples

Input types Common supertype Returns Notes
INT64
FLOAT64
FLOAT64 FLOAT64 If you apply supertyping to INT64 and FLOAT64, supertyping succeeds because they they share a supertype, FLOAT64.
INT64
BOOL
None Error If you apply supertyping to INT64 and BOOL, supertyping fails because they do not share a common supertype.

Exact and inexact types

Numeric types can be exact or inexact. For supertyping, if all of the input types are exact types, then the resulting supertype can only be an exact type.

The following table contains a list of exact and inexact numeric data types.

Exact types Inexact types
INT64
NUMERIC
FLOAT64

Examples

Input types Common supertype Returns Notes
INT64
FLOAT64
FLOAT64 FLOAT64 If supertyping is applied to INT64 and DOUBLE, supertyping succeeds because there are exact and inexact numeric types being supertyped.

Types specificity

Each type has a domain of values that it supports. A type with a narrow domain is more specific than a type with a wider domain. Exact types are more specific than inexact types because inexact types have a wider range of domain values that are supported than exact types. For example, INT64 is more specific than FLOAT64.

Supertypes and literals

Supertype rules for literals are more permissive than for normal expressions, and are consistent with implicit coercion rules. The following algorithm is used when the input set of types includes types related to literals:

  • If there exists non-literals in the set, find the set of common supertypes of the non-literals.
  • If there is at least one possible supertype, find the most specific type to which the remaining literal types can be implicitly coerced and return that supertype. Otherwise, there is no supertype.
  • If the set only contains types related to literals, compute the supertype of the literal types.
  • If all input types are related to NULL literals, then the resulting supertype is INT64.
  • If no common supertype is found, an error is produced.

Examples

Input types Common supertype Returns
INT64 literal
UINT64 expression
UINT64 UINT64
TIMESTAMP expression
STRING literal
TIMESTAMP TIMESTAMP
NULL literal
NULL literal
INT64 INT64
BOOL literal
TIMESTAMP literal
None Error