SQL: Fix incorrect HAVING equality

Fix bug that causes `HAVING a = b` to be translated ad-litteram in
Painless which uses `==` for equality checks not `=`.

Close elastic#31796

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/predicate/Equals.java

@@ -27,6 +27,7 @@ protected Equals replaceChildren(Expression newLeft, Expression newRight) {
         return new Equals(location(), newLeft, newRight);
     }
 
+    @Override
     public Object fold() {
         return Objects.equals(left().fold(), right().fold());
     }
@@ -38,6 +39,6 @@ public Equals swapLeftAndRight() {
 
     @Override
     public String symbol() {
-        return "=";
+        return "==";
     }
 }

x-pack/qa/sql/src/main/resources/agg.sql-spec

@@ -80,6 +80,8 @@ SELECT COUNT(DISTINCT hire_date) AS count FROM test_emp;
 // Conditional COUNT
 aggCountAndHaving
 SELECT gender g, COUNT(*) c FROM "test_emp" GROUP BY g HAVING COUNT(*) > 10 ORDER BY gender;
+aggCountAndHavingEquality
+SELECT gender g, COUNT(*) c FROM "test_emp" GROUP BY g HAVING COUNT(*) = 10 ORDER BY gender;
 aggCountOnColumnAndHaving
 SELECT gender g, COUNT(gender) c FROM "test_emp" GROUP BY g HAVING COUNT(gender) > 10 ORDER BY gender;
 // NOT supported yet since Having introduces a new agg
@@ -91,6 +93,8 @@ aggCountOnColumnAndHavingOnAlias
 SELECT gender g, COUNT(gender) c FROM "test_emp" GROUP BY g HAVING c > 10 ORDER BY gender;
 aggCountOnColumnAndMultipleHaving
 SELECT gender g, COUNT(gender) c FROM "test_emp" GROUP BY g HAVING c > 10 AND c < 70 ORDER BY gender ;
+aggCountOnColumnAndMultipleHavingEquals
+SELECT gender g, COUNT(gender) c FROM "test_emp" GROUP BY g HAVING c > 10 AND c = 63 ORDER BY gender ;
 aggCountOnColumnAndMultipleHavingWithLimit
 SELECT gender g, COUNT(gender) c FROM "test_emp" GROUP BY g HAVING c > 10 AND c < 70 ORDER BY gender LIMIT 1;
 aggCountOnColumnAndHavingBetween
@@ -145,6 +149,7 @@ SELECT gender g, MIN(emp_no) m FROM "test_emp" GROUP BY g HAVING m BETWEEN 10 AN
 aggMinWithMultipleHavingOnAliasAndFunction
 SELECT gender g, MIN(emp_no) m FROM "test_emp" GROUP BY g HAVING m > 10 AND MIN(emp_no) < 99999 ORDER BY gender;
 
+
 // MAX
 aggMaxImplicit
 // tag::max