Conversion rules

Google Standard SQL for BigQuery supports conversion. 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), but literals and parameters can also be coerced. See literal coercion and parameter coercion for details.

From type	Cast to	Coerce to
INT64	BOOL INT64 NUMERIC BIGNUMERIC FLOAT64 STRING	NUMERIC BIGNUMERIC FLOAT64
NUMERIC	INT64 NUMERIC BIGNUMERIC FLOAT64 STRING	BIGNUMERIC FLOAT64
BIGNUMERIC	INT64 NUMERIC BIGNUMERIC FLOAT64 STRING	FLOAT64
FLOAT64	INT64 NUMERIC BIGNUMERIC FLOAT64 STRING
BOOL	BOOL INT64 STRING
STRING	BOOL INT64 NUMERIC BIGNUMERIC FLOAT64 STRING BYTES DATE DATETIME TIME TIMESTAMP
BYTES	STRING BYTES
DATE	STRING DATE DATETIME TIMESTAMP	DATETIME
DATETIME	STRING DATE DATETIME TIME TIMESTAMP
TIME	STRING TIME
TIMESTAMP	STRING DATE DATETIME TIME 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.

Literal coercion

Google Standard SQL supports the following literal coercions:

Input data type	Result data type	Notes
STRING literal	DATE DATETIME TIME TIMESTAMP

Literal coercion is needed when the actual literal type is different from the type expected by the function in question. For example, if function func() takes a DATE argument, then the expression func("2014-09-27") is valid because the string literal "2014-09-27" is coerced to DATE.

Literal conversion is evaluated at analysis time, and gives an error if the input literal cannot be converted successfully to the target type.

Note: String literals do not coerce to numeric types.

Parameter coercion

Google Standard SQL supports the following parameter coercions:

Input data type	Result data type
STRING parameter	DATE DATETIME TIME TIMESTAMP

If the parameter value cannot be coerced successfully to the target type, an error is provided.

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 BIGNUMERIC
FLOAT64	FLOAT64
NUMERIC	NUMERIC BIGNUMERIC FLOAT64
DECIMAL	DECIMAL BIGDECIMAL FLOAT64
BIGNUMERIC	BIGNUMERIC FLOAT64
BIGDECIMAL	BIGDECIMAL FLOAT64
STRING	STRING
DATE	DATE
TIME	TIME
DATETIME	DATETIME
TIMESTAMP	TIMESTAMP
BYTES	BYTES
STRUCT	STRUCT with the same field position types.
ARRAY	ARRAY with the same element types.
GEOGRAPHY	GEOGRAPHY

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 BIGNUMERIC	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