fix + test handling of chr() on Oracle, Derby, MySQL

- Derby simply doesn't have it
- in MySQL it's necessary to specify the character set
- add ascii() and chr() to OracleDialect

hibernate-core/src/main/java/org/hibernate/dialect/DerbyDialect.java

@@ -256,7 +256,6 @@ public class DerbyDialect extends Dialect {
 
 		functionFactory.concat_pipeOperator();
 		functionFactory.cot();
-		functionFactory.chr_char();
 		functionFactory.degrees();
 		functionFactory.radians();
 		functionFactory.log10();

hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java

@@ -29,7 +29,6 @@ import java.time.temporal.TemporalAccessor;
 import java.util.Calendar;
 import java.util.Date;
 import java.util.HashSet;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;

hibernate-core/src/main/java/org/hibernate/dialect/MySQLDialect.java

@@ -54,6 +54,7 @@ import org.hibernate.query.sqm.mutation.internal.temptable.LocalTemporaryTableMu
 import org.hibernate.dialect.temptable.TemporaryTableKind;
 import org.hibernate.query.sqm.mutation.spi.SqmMultiTableInsertStrategy;
 import org.hibernate.query.sqm.mutation.spi.SqmMultiTableMutationStrategy;
+import org.hibernate.query.sqm.produce.function.FunctionParameterType;
 import org.hibernate.service.ServiceRegistry;
 import org.hibernate.sql.ast.SqlAstTranslator;
 import org.hibernate.sql.ast.SqlAstTranslatorFactory;
@@ -470,7 +471,6 @@ public class MySQLDialect extends Dialect {
 		functionFactory.bitLength();
 		functionFactory.octetLength();
 		functionFactory.ascii();
-		functionFactory.chr_char();
 		functionFactory.instr();
 		functionFactory.substr();
 		//also natively supports ANSI-style substring()
@@ -503,6 +503,12 @@ public class MySQLDialect extends Dialect {
 				.setArgumentListSignature("")
 				.register();
 
+		queryEngine.getSqmFunctionRegistry().patternDescriptorBuilder( "chr", "char(?1 using ascii)" )
+				.setInvariantType(basicTypeRegistry.resolve( StandardBasicTypes.CHARACTER ))
+				.setExactArgumentCount(1)
+				.setParameterTypes(FunctionParameterType.INTEGER)
+				.register();
+
 		// MySQL timestamp type defaults to precision 0 (seconds) but
 		// we want the standard default precision of 6 (microseconds)
 		functionFactory.sysdateExplicitMicros();

hibernate-core/src/main/java/org/hibernate/dialect/OracleDialect.java

@@ -15,7 +15,6 @@ import java.util.Locale;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-import org.hibernate.HibernateException;
 import org.hibernate.LockOptions;
 import org.hibernate.QueryTimeoutException;
 import org.hibernate.boot.model.TypeContributions;
@@ -141,6 +140,8 @@ public class OracleDialect extends Dialect {
 		final TypeConfiguration typeConfiguration = queryEngine.getTypeConfiguration();
 
 		CommonFunctionFactory functionFactory = new CommonFunctionFactory(queryEngine);
+		functionFactory.ascii();
+		functionFactory.char_chr();
 		functionFactory.cosh();
 		functionFactory.sinh();
 		functionFactory.tanh();

hibernate-core/src/test/java/org/hibernate/orm/test/query/hql/FunctionTests.java

@@ -331,6 +331,9 @@ public class FunctionTests {
 							.list();
 					session.createQuery("from EntityOfBasics e where chr(120) = 'z'")
 							.list();
+
+					assertThat( session.createQuery("select chr(65)").getSingleResult(), is('A') );
+					assertThat( session.createQuery("select ascii('A')").getSingleResult(), is(65) );
 				}
 		);
 	}