fix(mysql): correct TypeCast inference and add end-to-end tests

Author: rubensantoniorosa2704

internal/compiler/infer_expr_type.go

@@ -127,15 +127,16 @@ func (c *Compiler) inferMySQLTypeCast(node *ast.TypeCast, tables []*Table) Type
 		return unknownType()
 	}
 
-	base := toColumn(node.TypeName)
-	if base == nil {
+	// MySQL populates TypeName.Name directly; toColumn reads TypeName.Names (Postgres-style).
+	kind := mapMySQLKind(node.TypeName.Name)
+	if kind == KindUnknown {
 		return unknownType()
 	}
 
 	arg := c.inferMySQLExpr(node.Arg, tables)
 
 	t := Type{
-		Kind:  mapMySQLKind(base.DataType),
+		Kind:  kind,
 		Valid: true,
 	}
 

internal/endtoend/testdata/mysql_expression_type_inference/mysql/go/db.go

@@ -0,0 +1,11 @@
+-- name: FloatDivByConst :many
+SELECT (value / 1024) AS scaled_value FROM metrics;
+
+-- name: IntDivByConst :many
+SELECT (count / 10) AS avg_count FROM metrics;
+
+-- name: FloatDivByFloat :many
+SELECT (value / ratio) AS proportion FROM metrics;
+
+-- name: NotNullFloatDivByConst :many
+SELECT (CAST(value AS FLOAT) / 1024) AS scaled FROM metrics;

internal/endtoend/testdata/mysql_expression_type_inference/mysql/go/models.go

@@ -0,0 +1,6 @@
+CREATE TABLE metrics (
+    id      INT          NOT NULL PRIMARY KEY,
+    value   FLOAT        NULL,
+    count   INT          NOT NULL,
+    ratio   DOUBLE       NULL
+);

internal/endtoend/testdata/mysql_expression_type_inference/mysql/go/query.sql.go

@@ -0,0 +1,14 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "sql_package": "database/sql",
+      "sql_driver": "github.com/go-sql-driver/mysql",
+      "engine": "mysql",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}