Conversion rules

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GoogleSQL for Bigtable 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 GoogleSQL 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 GoogleSQL 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 FLOAT32 FLOAT64 STRING ENUM	FLOAT64
FLOAT32	INT64 FLOAT32 FLOAT64 STRING	FLOAT64
FLOAT64	INT64 FLOAT32 FLOAT64 STRING
BOOL	BOOL INT64 STRING
STRING	BOOL INT64 FLOAT32 FLOAT64 STRING BYTES DATE TIMESTAMP ENUM
BYTES	STRING BYTES
DATE	STRING DATE TIMESTAMP
TIMESTAMP	STRING DATE TIMESTAMP
ARRAY	ARRAY
ENUM	ENUM (with the same ENUM name) INT64 STRING	ENUM (with the same ENUM name)
MAP	MAP (with castable key and value types)	MAP (with coercible key and value types)
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 GoogleSQL 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

GoogleSQL 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

GoogleSQL supports the following literal coercions:

Input data type	Result data type	Notes
FLOAT64 literal	FLOAT32	Coercion may not be exact, and returns a close value.
STRING literal	DATE TIMESTAMP ENUM

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.

Parameter coercion

GoogleSQL supports the following parameter coercions:

Input data type	Result data type
INT64 parameter	ENUM
MAP parameter	MAP Coercion is allowed from MAP<K1, V1> to MAP<K2, V2> if K2 and V2 are supertypes of K1 and V1.
STRING parameter	DATE TIMESTAMP ENUM

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 FLOAT32 FLOAT64
FLOAT32	FLOAT32 FLOAT64
FLOAT64	FLOAT64
DECIMAL	DECIMAL BIGDECIMAL FLOAT64
BIGDECIMAL	BIGDECIMAL FLOAT64
STRING	STRING
DATE	DATE
TIMESTAMP	TIMESTAMP
ENUM	ENUM with the same name. The resulting enum supertype is the one that occurred first.
BYTES	BYTES
STRUCT	STRUCT with the same field position types.
ARRAY	ARRAY with the same element types.
MAP	MAP<K1, V1> is a supertype of MAP<K2, V2> if K1 and V1 are supertypes of K2 and V2.

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 FLOAT32	FLOAT64	FLOAT64	If you apply supertyping to INT64 and FLOAT32, supertyping succeeds because they they share a supertype, FLOAT64.
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	FLOAT32 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
FLOAT64 literal FLOAT32 expression	FLOAT32	FLOAT32
INT64 literal FLOAT64 literal	FLOAT64	FLOAT64
TIMESTAMP expression STRING literal	TIMESTAMP	TIMESTAMP
NULL literal NULL literal	INT64	INT64
BOOL literal TIMESTAMP literal	None	Error