Use primary table alias for SQL count query derivation with DISTINCT queries.

We now use render COUNT(DISTINCT a.*) where 'a' is the primary table alias instead of COUNT(DISTINCT *).

Closes #3707

Author: mp911de

spring-data-jpa/src/main/java/org/springframework/data/jpa/repository/query/JSqlParserQueryEnhancer.java

@@ -354,11 +354,11 @@ public String createCountQueryFor(@Nullable String countProjection) {
 			return this.query.getQueryString();
 		}
 
-		return createCountQueryFor(this.query, selectBody, countProjection);
+		return createCountQueryFor(this.query, selectBody, countProjection, primaryAlias);
 	}
 
 	private static String createCountQueryFor(DeclaredQuery query, PlainSelect selectBody,
-			@Nullable String countProjection) {
+			@Nullable String countProjection, @Nullable String primaryAlias) {
 
 		// remove order by
 		selectBody.setOrderByElements(null);
@@ -373,7 +373,8 @@ private static String createCountQueryFor(DeclaredQuery query, PlainSelect selec
 			selectBody.setDistinct(null); // reset possible distinct
 
 			Function jSqlCount = getJSqlCount(
-					Collections.singletonList(countPropertyNameForSelection(selectBody.getSelectItems(), distinct)), distinct);
+					Collections.singletonList(countPropertyNameForSelection(selectBody.getSelectItems(), distinct, primaryAlias)),
+					distinct);
 			selectBody.setSelectItems(Collections.singletonList(SelectItem.from(jSqlCount)));
 		}
 
@@ -463,7 +464,8 @@ private static OrderByElement getOrderClause(Set<String> joinAliases, Set<String
 	 * @param tableAlias the table alias which can be {@literal null}.
 	 * @return
 	 */
-	private static String countPropertyNameForSelection(List<SelectItem<?>> selectItems, boolean distinct) {
+	private static String countPropertyNameForSelection(List<SelectItem<?>> selectItems, boolean distinct,
+			@Nullable String tableAlias) {
 
 		if (onlyASingleColumnProjection(selectItems)) {
 
@@ -472,7 +474,7 @@ private static String countPropertyNameForSelection(List<SelectItem<?>> selectIt
 			return column.getFullyQualifiedName();
 		}
 
-		return (distinct ? "*" : "1");
+		return distinct ? ((tableAlias != null ? tableAlias + "." : "") + "*") : "1";
 	}
 
 	/**

spring-data-jpa/src/test/java/org/springframework/data/jpa/repository/query/JSqlParserQueryEnhancerUnitTests.java

@@ -51,6 +51,22 @@ void shouldApplySorting() {
 		assertThat(sql).isEqualTo("SELECT e FROM Employee e ORDER BY e.foo ASC, e.bar ASC");
 	}
 
+	@Test // GH-3707
+	void countQueriesShouldConsiderPrimaryTableAlias() {
+
+		QueryEnhancer enhancer = createQueryEnhancer(DeclaredQuery.of("""
+				SELECT DISTINCT a.*, b.b1
+				FROM TableA a
+				  JOIN TableB b ON a.b = b.b
+				  LEFT JOIN TableC c ON b.c = c.c
+				ORDER BY b.b1, a.a1, a.a2
+				""", true));
+
+		String sql = enhancer.createCountQueryFor();
+
+		assertThat(sql).startsWith("SELECT count(DISTINCT a.*) FROM TableA a");
+	}
+
 	@Override
 	@ParameterizedTest // GH-2773
 	@MethodSource("jpqlCountQueries")