ENG-7840 fix null in indexed expressions, add fullDDL cases for this and...

src/frontend/org/voltdb/expressions/ConstantValueExpression.java

@@ -430,6 +430,9 @@ public boolean isPrefixPatternString() {
 
     @Override
     public String explain(String unused) {
+        if (m_isNull) {
+            return "NULL";
+        }
         if (m_valueType == VoltType.STRING) {
             return "'" + m_value + "'";
         }

tests/frontend/org/voltdb/fullddlfeatures/fullDDL.sql

@@ -876,3 +876,47 @@ T54
     C2
 );
 ALTER TABLE T54 ALTER COLUMN C2 VARCHAR(2) CASCADE;
+
+CREATE TABLE T55
+(
+    STR VARCHAR(30)
+,   TS TIMESTAMP
+,   BIG BIGINT    
+);
+
+-- These statements were added when use of some Volt-specific functions or ||
+-- or NULL in indexed expressions was discovered to be mishandled (ENG-7792).
+-- They showed that views and procs did NOT share these problems,
+-- but let's make sure things stay that way.
+CREATE PROCEDURE PROC_USES_CONCAT AS SELECT CONCAT(SUBSTRING(STR,4), SUBSTRING(STR,1,3)) FROM T55;
+CREATE PROCEDURE PROC_USES_BARBARCONCAT AS SELECT SUBSTRING(STR,5) || SUBSTRING(STR,1,3) FROM T55;
+CREATE PROCEDURE PROC_USES_NULL AS SELECT DECODE(STR, NULL, 'NULLISH', STR) FROM T55;
+CREATE PROCEDURE PROC_USES_TO_TIMESTAMP AS SELECT TO_TIMESTAMP(SECOND, BIG) FROM T55;
+CREATE VIEW V55_USES_NULL AS
+    SELECT   DECODE(STR, NULL, 'NULLISH', STR), COUNT(*), SUM(BIG)
+    FROM T55 
+    GROUP BY DECODE(STR, NULL, 'NULLISH', STR);
+CREATE VIEW V55_USES_TO_TIMESTAMP AS
+    SELECT   TO_TIMESTAMP(SECOND, BIG), COUNT(*), COUNT(STR)
+    FROM T55 
+    GROUP BY TO_TIMESTAMP(SECOND, BIG);
+CREATE VIEW V55_USES_CONCAT AS
+    SELECT   CONCAT(SUBSTRING(STR,4), SUBSTRING(STR,1,3)), COUNT(*), COUNT(STR)
+    FROM T55 
+    GROUP BY CONCAT(SUBSTRING(STR,4), SUBSTRING(STR,1,3));
+CREATE VIEW V55_USES_BARBARCONCAT AS
+    SELECT   SUBSTRING(STR,5) || SUBSTRING(STR,1,3), COUNT(*), COUNT(STR)
+    FROM T55 
+    GROUP BY SUBSTRING(STR,5) || SUBSTRING(STR,1,3);
+
+-- ENG-7792 Make sure that concat, ||, and volt-specific SQL functions survive DDL roundtripping.
+-- This especially exercises FunctionForVoltDB.getSQL().
+CREATE INDEX ENG7792_INDEX_USES_CONCAT ON T55 (CONCAT(SUBSTRING(STR,4), SUBSTRING(STR,1,3)));
+CREATE INDEX ENG7792_INDEX_USES_BARBARCONCAT ON T55 (SUBSTRING(STR,5) || SUBSTRING(STR,1,3));
+-- ENG-7840 Make sure that a NULL constant survives DDL roundtripping.
+CREATE INDEX ENG7840_INDEX_USES_NULL ON T55 (DECODE(STR, NULL, 'NULLISH', STR));
+CREATE INDEX INDEX_USES_DECODE ON T55 (DECODE(STR, '', 'NULLISH', STR));
+CREATE INDEX INDEX_USES_SINCE_EPOCH ON T55 (SINCE_EPOCH(SECOND, TS)/60);
+CREATE INDEX INDEX_USES_TRUNCATE_AND_TO_TIMESTAMP ON T55 (TRUNCATE(DAY, TO_TIMESTAMP(SECOND, BIG)));
+CREATE INDEX INDEX_USES_JSON_SET_FIELD_ON_FIELD ON T55 (SET_FIELD(FIELD(STR, 'A'), 'B', ''));
+CREATE INDEX INDEX_USES_JSON_ARRAY_OPS ON T55 (ARRAY_ELEMENT(STR, ARRAY_LENGTH(STR)-1));