Conversion rules in GoogleSQL

GoogleSQL for Spanner 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).

From type	Cast to	Coerce to
`INT64`	`BOOL` `INT64` `NUMERIC` `FLOAT32` `FLOAT64` `STRING` `ENUM`	`NUMERIC` `FLOAT64`
`NUMERIC`	`INT64` `NUMERIC` `FLOAT32` `FLOAT64` `STRING`	`FLOAT64`
`FLOAT32`	`INT64` `NUMERIC` `FLOAT32` `FLOAT64` `STRING`	`FLOAT64`
`FLOAT64`	`INT64` `NUMERIC` `FLOAT32` `FLOAT64` `STRING`
`BOOL`	`BOOL` `INT64` `STRING`
`STRING`	`BOOL` `INT64` `NUMERIC` `FLOAT32` `FLOAT64` `STRING` `BYTES` `DATE` `TIMESTAMP` `ENUM` `PROTO`
`BYTES`	`STRING` `BYTES` `PROTO`
`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)
`STRUCT`	`STRUCT`
`PROTO`	`PROTO` (with the same `PROTO` name) `STRING` `BYTES`	`PROTO` (with the same `PROTO` name)

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.

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` `NUMERIC`
`FLOAT32`	`FLOAT32` `FLOAT64`
`FLOAT64`	`FLOAT64`
`NUMERIC`	`NUMERIC` `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.
`PROTO`	`PROTO` with the same name. The resulting `PROTO` supertype is the one that occurred first. For example, the first occurrence could be in the first branch of a set operation or the first result expression in a `CASE` statement.
`GRAPH_ELEMENT`	`GRAPH_ELEMENT`. A graph element can be a supertype of another graph element if the following is true: Graph element `a` is a supertype of graph element `b` and they're the same element kind. Graph element `a`'s property type list is a compatible superset of graph element `b`'s property type list. This means that properties with the same name must also have the same type.

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` `NUMERIC`	`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