SQL: Allow look-ahead resolution of aliases for WHERE clause

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/analysis/analyzer/Analyzer.java

@@ -105,6 +105,7 @@ protected Iterable<RuleExecutor<LogicalPlan>.Batch> batches() {
                 new ResolveRefs(),
                 new ResolveOrdinalInOrderByAndGroupBy(),
                 new ResolveMissingRefs(),
+                new ResolveFilterRefs(),
                 new ResolveFunctions(),
                 new ResolveAliases(),
                 new ProjectedAggregations(),
@@ -762,6 +763,68 @@ private static UnresolvedAttribute resolveMetadataToMessage(UnresolvedAttribute
         }
     }
 
+    //
+    // Resolve aliases defined in SELECT that are referred inside the WHERE clause:
+    // SELECT int AS i FROM t WHERE i > 10
+    //
+    // As such, identify all project and aggregates that have a Filter child
+    // and look at any resoled aliases that match and replace them.
+    private class ResolveFilterRefs extends AnalyzeRule<LogicalPlan> {
+
+        @Override
+        protected LogicalPlan rule(LogicalPlan plan) {
+            if (plan instanceof Project) {
+                Project p = (Project) plan;
+                if (p.child() instanceof Filter) {
+                    Filter f = (Filter) p.child();
+                    Expression condition = f.condition();
+                    if (condition.resolved() == false && f.childrenResolved() == true) {
+                        Expression newCondition = replaceAliases(condition, p.projections());
+                        if (newCondition != condition) {
+                            return new Project(p.source(), new Filter(f.source(), f.child(), newCondition), p.projections());
+                        }
+                    }
+                }
+            }
+
+            if (plan instanceof Aggregate) {
+                Aggregate a = (Aggregate) plan;
+                if (a.child() instanceof Filter) {
+                    Filter f = (Filter) a.child();
+                    Expression condition = f.condition();
+                    if (condition.resolved() == false && f.childrenResolved() == true) {
+                        Expression newCondition = replaceAliases(condition, a.aggregates());
+                        if (newCondition != condition) {
+                            return new Aggregate(a.source(), new Filter(f.source(), f.child(), newCondition), a.groupings(),
+                                    a.aggregates());
+                        }
+                    }
+                }
+            }
+
+            return plan;
+        }
+
+        private Expression replaceAliases(Expression condition, List<? extends NamedExpression> named) {
+            List<Alias> aliases = new ArrayList<>();
+            named.forEach(n -> {
+                if (n instanceof Alias) {
+                    aliases.add((Alias) n);
+                }
+            });
+
+            return condition.transformDown(u -> {
+                boolean qualified = u.qualifier() != null;
+                for (Alias alias : aliases) {
+                    if (qualified ? Objects.equals(alias.qualifiedName(), u.qualifiedName()) : Objects.equals(alias.name(), u.name())) {
+                        return alias;
+                    }
+                }
+                return u;
+             }, UnresolvedAttribute.class);
+        }
+    }
+
     // to avoid creating duplicate functions
     // this rule does two iterations
     // 1. collect all functions

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

@@ -7,8 +7,8 @@
 
 import org.elasticsearch.xpack.sql.SqlIllegalArgumentException;
 import org.elasticsearch.xpack.sql.expression.gen.script.ScriptTemplate;
-import org.elasticsearch.xpack.sql.tree.Source;
 import org.elasticsearch.xpack.sql.tree.NodeInfo;
+import org.elasticsearch.xpack.sql.tree.Source;
 import org.elasticsearch.xpack.sql.type.DataType;
 import org.elasticsearch.xpack.sql.type.EsField;
 
@@ -75,6 +75,10 @@ public String qualifier() {
         return qualifier;
     }
 
+    public String qualifiedName() {
+        return qualifier == null ? name() : qualifier + "." + name();
+    }
+
     @Override
     public Nullability nullable() {
         return child.nullable();

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/analysis/analyzer/VerifierErrorMessagesTests.java

@@ -638,5 +638,16 @@ public void testMaxOnKeywordGroupByHavingUnsupported() {
         assertEquals("1:52: HAVING filter is unsupported for function [MAX(keyword)]",
             error("SELECT MAX(keyword) FROM test GROUP BY text HAVING MAX(keyword) > 10"));
     }
-}
 
+    public void testProjectAliasInFilter() {
+        accept("SELECT int AS i FROM test WHERE i > 10");
+    }
+
+    public void testAggregateAliasInFilter() {
+        accept("SELECT int AS i FROM test WHERE i > 10 GROUP BY i HAVING MAX(i) > 10");
+    }
+
+    public void testProjectUnresolvedAliasInFilter() {
+        assertEquals("1:8: Unknown column [tni]", error("SELECT tni AS i FROM test WHERE i > 10 GROUP BY i"));
+    }
+}