Address comments

docs/reference/sql/functions/grouping.asciidoc

@@ -77,7 +77,8 @@ Instead one can rewrite the query to move the expression on the histogram _insid
 include-tagged::{sql-specs}/docs.csv-spec[histogramDateTimeExpression]
 ----
 
-[NOTE]
-When the histogram in SQL is applied on **DATE** type instead of **DATETIME**, then the interval specified is rounded to
-the nearest multiple of a day. E.g.: for `HISTOGRAM(CAST(birth_date AS DATE), INTERVAL '2 3:04' DAY TO MINUTE)`
-the interval actually used will be `INTERVAL 2 DAYS`.
+[IMPORTANT]
+When the histogram in SQL is applied on **DATE** type instead of **DATETIME**, the interval specified is truncated to
+the multiple of a day. E.g.: for `HISTOGRAM(CAST(birth_date AS DATE), INTERVAL '2 3:04' DAY TO MINUTE)` the interval
+actually used will be `INTERVAL '2' DAY`. If the interval specified is less than 1 day, e.g.:
+`HISTOGRAM(CAST(birth_date AS DATE), INTERVAL '20' HOUR)` then the interval used will be `INTERVAL '1' DAY`.

x-pack/plugin/sql/qa/src/main/resources/date.csv-spec

@@ -58,19 +58,6 @@ SELECT birth_date, last_name FROM "test_emp" WHERE birth_date <= CAST('1955-01-2
 1952-04-19T00:00:00Z  |Peac
 ;
 
-
-// The date return can differ due to the randomized timezones (it's transformed to the JDBC client's timezone)
-dateAsGroupingKey-Ignore
-SELECT CAST(birth_date AS DATE) AS d, CAST(SUM(emp_no) AS INT) s FROM test_emp GROUP BY d ORDER BY d LIMIT 5;
-
- d:date     | s:i
-null        |100445
-1952-02-26  |10097
-1952-04-18  |10009
-1952-05-14  |10072
-1952-06-12  |10076
-;
-
 dateAndFunctionAsGroupingKey
 SELECT MONTH(CAST(birth_date AS DATE)) AS m, CAST(SUM(emp_no) AS INT) s FROM test_emp GROUP BY m ORDER BY m LIMIT 5;
 

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/predicate/operator/arithmetic/DateTimeArithmeticOperation.java

@@ -6,6 +6,7 @@
 
 package org.elasticsearch.xpack.sql.expression.predicate.operator.arithmetic;
 
+import org.elasticsearch.xpack.sql.SqlIllegalArgumentException;
 import org.elasticsearch.xpack.sql.expression.Expression;
 import org.elasticsearch.xpack.sql.expression.predicate.operator.arithmetic.BinaryArithmeticProcessor.BinaryArithmeticOperation;
 import org.elasticsearch.xpack.sql.tree.Source;
@@ -14,6 +15,7 @@
 import org.elasticsearch.xpack.sql.type.DataTypes;
 
 import static org.elasticsearch.common.logging.LoggerMessageFormat.format;
+import static org.elasticsearch.xpack.sql.expression.predicate.operator.arithmetic.BinaryArithmeticProcessor.BinaryArithmeticOperation.SUB;
 
 abstract class DateTimeArithmeticOperation extends ArithmeticOperation {
 
@@ -45,6 +47,9 @@ protected TypeResolution resolveType() {
             if (DataTypeConversion.commonType(l, r) == null) {
                 return new TypeResolution(format("[{}] has arguments with incompatible types [{}] and [{}]", symbol(), l, r));
             } else {
+                if (function() == SUB && right().dataType().isDateBased() && DataTypes.isInterval(left().dataType())) {
+                    throw new SqlIllegalArgumentException("Cannot subtract a date from an interval; do you mean the reverse?");
+                }
                 return TypeResolution.TYPE_RESOLVED;
             }
         }

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/type/DataTypeConversion.java

@@ -87,12 +87,18 @@ public static DataType commonType(DataType left, DataType right) {
             }
         }
         if (left == DATETIME) {
-            if (right == DATE || DataTypes.isInterval(right)) {
+            if (right == DATE) {
+                return left;
+            }
+            if (DataTypes.isInterval(right)) {
                 return left;
             }
         }
         if (right == DATETIME) {
-            if (left == DATE || DataTypes.isInterval(left)) {
+            if (left == DATE) {
+                return right;
+            }
+            if (DataTypes.isInterval(left)) {
                 return right;
             }
         }

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

@@ -198,6 +198,14 @@ public void testExtractNonDateTime() {
         assertEquals("1:8: Invalid datetime field [ABS]. Use any datetime function.", error("SELECT EXTRACT(ABS FROM date) FROM test"));
     }
 
+    public void testSubtractFromInterval() {
+        Analyzer analyzer = new Analyzer(TestUtils.TEST_CFG, new FunctionRegistry(), indexResolution, new Verifier(new Metrics()));
+        SqlIllegalArgumentException e = expectThrows(SqlIllegalArgumentException.class, () -> analyzer.analyze(parser.createStatement(
+            "SELECT INTERVAL 1 MONTH - CAST('2000-01-01' AS DATETIME)"), true));
+        assertEquals("Cannot subtract a date from an interval; do you mean the reverse?",
+            e.getMessage());
+    }
+
     public void testMultipleColumns() {
         // xxx offset is that of the order by field
         assertEquals("1:43: Unknown column [xxx]\nline 1:8: Unknown column [xxx]",