julianhyde commented on code in PR #3258:
URL: https://github.com/apache/calcite/pull/3258#discussion_r1232532361
##########
core/src/test/resources/sql/functions.iq:
##########
@@ -499,6 +510,144 @@ select CONVERT(DATE, '05/01/2000', 103);
!ok
!}
+# [CALCITE-5771] Apply two different NULL semantics for CONCAT
function(enabled in MySQL, Postgresql, BigQuery and MSSQL)
+select concat(null);
++--------+
+| EXPR$0 |
++--------+
+| |
++--------+
+(1 row)
+
+!ok
+
+select concat(null, '');
++--------+
+| EXPR$0 |
++--------+
+| |
++--------+
+(1 row)
+
+!ok
+
+select concat('', '');
++--------+
+| EXPR$0 |
++--------+
+| |
++--------+
+(1 row)
+
+!ok
+
+select concat('a', null, 'b');
++--------+
+| EXPR$0 |
++--------+
+| ab |
++--------+
+(1 row)
+
+!ok
+
+select concat('a', cast(null as varchar), 'b');
++--------+
+| EXPR$0 |
++--------+
+| ab |
++--------+
+(1 row)
+
+!ok
+
+select concat(cast(null as varchar), 'a', 'b');
++--------+
+| EXPR$0 |
++--------+
+| ab |
++--------+
+(1 row)
+
+!ok
+
+select concat(null, null, null);
++--------+
+| EXPR$0 |
++--------+
+| |
++--------+
+(1 row)
+
+!ok
+
+# test that col1 is empty string rather than NULL
+with v as (select concat(null, '') as col1, 'b' as col2)
+select col2 from v where col1='';
++------+
+| COL2 |
++------+
+| b |
++------+
+(1 row)
+
+!ok
+
+# concat in BigQuery
+!use post-big-query
+
+select concat('a');
++--------+
+| EXPR$0 |
++--------+
+| a |
++--------+
+(1 row)
+
+!ok
+
+select concat('a', 'b');
++--------+
+| EXPR$0 |
++--------+
+| ab |
++--------+
+(1 row)
+
+!ok
+
+select concat('a', cast(null as varchar), 'b');
++--------+
+| EXPR$0 |
++--------+
+| |
++--------+
+(1 row)
+
+!ok
+
+select concat(null, null, null);
++--------+
+| EXPR$0 |
++--------+
+| |
++--------+
+(1 row)
+
+!ok
+
Review Comment:
Quidem's output format isn't helpful here, because it prints empty strings
the same as null.
May I suggest that you make each test print the value and also print whether
that value is null, e.g.
```
with t as (select concat(null, null, null) as c)
select c, c is null as c_is_null
from t;
```
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