Support casting to ``FLOAT`` in MySQL and MariaDb.

Fixes: #5808
Change-Id: I8106ddcf681eec3cb3a67d853586702f6e844b9d

1 files changed, 17 insertions, 1 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 7a4d3261f..a4b583541 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -1624,6 +1624,11 @@ class MySQLCompiler(compiler.SQLCompiler):
             return self.dialect.type_compiler.process(type_).replace(
                 "NUMERIC", "DECIMAL"
             )
+        elif (
+            isinstance(type_, sqltypes.Float)
+            and self.dialect._support_float_cast
+        ):
+            return self.dialect.type_compiler.process(type_)
         else:
             return None
 
@@ -1631,7 +1636,7 @@ class MySQLCompiler(compiler.SQLCompiler):
         type_ = self.process(cast.typeclause)
         if type_ is None:
             util.warn(
-                "Datatype %s does not support CAST on MySQL; "
+                "Datatype %s does not support CAST on MySQL/MariaDb; "
                 "the CAST will be skipped."
                 % self.dialect.type_compiler.process(cast.typeclause.type)
             )
@@ -2900,6 +2905,17 @@ class MySQLDialect(default.DefaultDialect):
                 )
 
     @property
+    def _support_float_cast(self):
+        if not self.server_version_info:
+            return False
+        elif self.is_mariadb:
+            # ref https://mariadb.com/kb/en/mariadb-1045-release-notes/
+            return self.server_version_info >= (10, 4, 5)
+        else:
+            # ref https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-17.html#mysqld-8-0-17-feature  # noqa
+            return self.server_version_info >= (8, 0, 17)
+
+    @property
     def _is_mariadb(self):
         return self.is_mariadb