fix MySql + add more tests to SqlCurrency

Author: mythz

src/ServiceStack.OrmLite.MySql/MySqlDialectProvider.cs

@@ -209,7 +209,7 @@ public string GetColumnDefinition(FieldDefinition fieldDef)
         }
 
         public override string SqlCurrency(string fieldOrValue, string currencySymbol) => 
-            SqlConcat(new []{ "'" + currencySymbol + "'", "format(" + fieldOrValue + ",2)"});
+            SqlConcat(new []{ "'" + currencySymbol + "'", "cast(" + fieldOrValue + " as decimal(15,2))" });
 
         protected MySqlConnection Unwrap(IDbConnection db)
         {

tests/ServiceStack.OrmLite.Tests/SqlDialectTests.cs

@@ -13,6 +13,8 @@ public class Sqltest
 
     public class SqlDialectTests : OrmLiteTestBase
     {
+        //public SqlDialectTests() : base(Dialect.PostgreSql) {}
+
         [Test]
         public void Does_concat_values()
         {
@@ -40,6 +42,15 @@ public void Does_format_currency()
                 db.DropAndCreateTable<Sqltest>();
 
                 db.Insert(new Sqltest { Value = 12 });
+
+                var sqlCurrency = db.GetDialectProvider().SqlCurrency("12.3456");
+                var result = db.Scalar<string>($"SELECT {sqlCurrency} from sqltest");
+                Assert.That(result, Is.EqualTo("$12.35"));
+
+                sqlCurrency = db.GetDialectProvider().SqlCurrency("12.3456", "£");
+                result = db.Scalar<string>($"SELECT {sqlCurrency} from sqltest");
+                Assert.That(result, Is.EqualTo("£12.35"));
+
                 db.Insert(new Sqltest { Value = 12.3 });
                 db.Insert(new Sqltest { Value = 12.34 });
                 db.Insert(new Sqltest { Value = 12.345 });