fix: do not enforce type equality if matching against the NULL type

sqlx-core/src/any/type_info.rs

@@ -33,6 +33,22 @@ pub(crate) enum AnyTypeInfoKind {
 }
 
 impl TypeInfo for AnyTypeInfo {
+    fn is_null(&self) -> bool {
+        match &self.0 {
+            #[cfg(feature = "postgres")]
+            AnyTypeInfoKind::Postgres(ty) => ty.is_null(),
+
+            #[cfg(feature = "mysql")]
+            AnyTypeInfoKind::MySql(ty) => ty.is_null(),
+
+            #[cfg(feature = "sqlite")]
+            AnyTypeInfoKind::Sqlite(ty) => ty.is_null(),
+
+            #[cfg(feature = "mssql")]
+            AnyTypeInfoKind::Mssql(ty) => ty.is_null(),
+        }
+    }
+
     fn name(&self) -> &str {
         match &self.0 {
             #[cfg(feature = "postgres")]

sqlx-core/src/mssql/type_info.rs

@@ -1,6 +1,6 @@
 use std::fmt::{self, Display, Formatter};
 
-use crate::mssql::protocol::type_info::TypeInfo as ProtocolTypeInfo;
+use crate::mssql::protocol::type_info::{TypeInfo as ProtocolTypeInfo, DataType};
 use crate::type_info::TypeInfo;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -8,6 +8,10 @@ use crate::type_info::TypeInfo;
 pub struct MssqlTypeInfo(pub(crate) ProtocolTypeInfo);
 
 impl TypeInfo for MssqlTypeInfo {
+    fn is_null(&self) -> bool {
+        matches!(self.0.ty, DataType::Null)
+    }
+
     fn name(&self) -> &str {
         self.0.name()
     }

sqlx-core/src/mysql/type_info.rs

@@ -60,6 +60,10 @@ impl Display for MySqlTypeInfo {
 }
 
 impl TypeInfo for MySqlTypeInfo {
+    fn is_null(&self) -> bool {
+        matches!(self.r#type, ColumnType::Null)
+    }
+
     fn name(&self) -> &str {
         self.r#type.name(self.char_set, self.flags)
     }

sqlx-core/src/postgres/type_info.rs

@@ -741,6 +741,10 @@ impl TypeInfo for PgTypeInfo {
     fn name(&self) -> &str {
         self.0.display_name()
     }
+
+    fn is_null(&self) -> bool {
+        false
+    }
 }
 
 impl PartialEq<PgCustomType> for PgCustomType {

sqlx-core/src/postgres/types/record.rs

@@ -6,6 +6,7 @@ use crate::error::{mismatched_types, BoxDynError};
 use crate::postgres::type_info::{PgType, PgTypeKind};
 use crate::postgres::{PgArgumentBuffer, PgTypeInfo, PgValueFormat, PgValueRef, Postgres};
 use crate::types::Type;
+use crate::type_info::TypeInfo;
 
 #[doc(hidden)]
 pub struct PgRecordEncoder<'a> {
@@ -126,7 +127,7 @@ impl<'r> PgRecordDecoder<'r> {
                 self.ind += 1;
 
                 if let Some(ty) = &element_type_opt {
-                    if !T::compatible(ty) {
+                    if !ty.is_null() && !T::compatible(ty) {
                         return Err(mismatched_types::<Postgres, T>(ty));
                     }
                 }

sqlx-core/src/row.rs

@@ -4,6 +4,7 @@ use crate::database::{Database, HasValueRef};
 use crate::decode::Decode;
 use crate::error::{mismatched_types, Error};
 use crate::types::Type;
+use crate::type_info::TypeInfo;
 use crate::value::ValueRef;
 
 /// A type that can be used to index into a [`Row`].
@@ -171,7 +172,7 @@ pub trait Row: private_row::Sealed + Unpin + Send + Sync + 'static {
         if !value.is_null() {
             let ty = value.type_info();
 
-            if !T::compatible(&ty) {
+            if !ty.is_null() && !T::compatible(&ty) {
                 return Err(Error::ColumnDecode {
                     index: format!("{:?}", index),
                     source: mismatched_types::<Self::Database, T>(&ty),

sqlx-core/src/sqlite/type_info.rs

@@ -40,6 +40,10 @@ impl Display for SqliteTypeInfo {
 }
 
 impl TypeInfo for SqliteTypeInfo {
+    fn is_null(&self) -> bool {
+        matches!(self.0, DataType::Null)
+    }
+
     fn name(&self) -> &str {
         match self.0 {
             DataType::Null => "NULL",

sqlx-core/src/type_info.rs

@@ -2,6 +2,8 @@ use std::fmt::{Debug, Display};
 
 /// Provides information about a SQL type for the database driver.
 pub trait TypeInfo: Debug + Display + Clone + PartialEq<Self> {
+    fn is_null(&self) -> bool;
+
     /// Returns the database system name of the type. Length specifiers should not be included.
     /// Common type names are `VARCHAR`, `TEXT`, or `INT`. Type names should be uppercase. They
     /// should be a rough approximation of how they are written in SQL in the given database.

sqlx-core/src/value.rs

@@ -2,6 +2,7 @@ use crate::database::{Database, HasValueRef};
 use crate::decode::Decode;
 use crate::error::{mismatched_types, Error};
 use crate::types::Type;
+use crate::type_info::TypeInfo;
 
 /// An owned value from the database.
 pub trait Value {
@@ -65,7 +66,7 @@ pub trait Value {
         if !self.is_null() {
             let ty = self.type_info();
 
-            if !T::compatible(&ty) {
+            if !ty.is_null() && !T::compatible(&ty) {
                 return Err(Error::Decode(mismatched_types::<Self::Database, T>(&ty)));
             }
         }