[UT] Add SQL test for sync-MV CASE WHEN/IF rewrite with widening sum

Covers the planner fix in MaterializedViewRewriter where a sync MV's
column-ref substitution was leaving the wrapping IF / CASE WHEN with the
original (narrower) declared result type, silently truncating outer
sum() values that exceeded that range.

Per-(k1, k2) sum(k3) is set up to overflow SMALLINT (sum reaches 100000
for one group), so the test would observe a truncated value in sum2 /
sum_if before the fix.

Author: claude

test/sql/test_materialized_view_rewrite/R/test_mv_rewrite_case_when_sum_widening_type.sql

@@ -0,0 +1,48 @@
+-- name: test_mv_rewrite_case_when_sum_widening_type
+create database db_${uuid0};
+-- result:
+-- !result
+use db_${uuid0};
+-- result:
+-- !result
+CREATE TABLE t1 (
+    k1 DATE NULL,
+    k2 INT  NULL,
+    k3 SMALLINT NULL
+) DUPLICATE KEY(k1)
+DISTRIBUTED BY HASH(k1) BUCKETS 1
+PROPERTIES("replication_num" = "1");
+-- result:
+-- !result
+CREATE MATERIALIZED VIEW test_mv1 AS
+  SELECT k1, k2, sum(k3) AS sum1 FROM t1 GROUP BY k1, k2;
+-- result:
+-- !result
+function: wait_materialized_view_finish()
+-- result:
+None
+-- !result
+INSERT INTO t1 VALUES
+    ('2024-01-01', 0, 30000),
+    ('2024-01-01', 0, 30000),
+    ('2024-01-01', 0, 30000),
+    ('2024-01-01', 0, 10000),
+    ('2024-01-01', 1, 5);
+-- result:
+-- !result
+SELECT k1,
+       sum(k3) AS sum1,
+       sum(case when k2=0 then k3 else 0 end) AS sum2
+FROM t1 GROUP BY k1;
+-- result:
+2024-01-01	100005	100000
+-- !result
+SELECT k1,
+       sum(if(k2=0, k3, 0)) AS sum_if
+FROM t1 GROUP BY k1;
+-- result:
+2024-01-01	100000
+-- !result
+DROP DATABASE db_${uuid0};
+-- result:
+-- !result

test/sql/test_materialized_view_rewrite/T/test_mv_rewrite_case_when_sum_widening_type.sql

@@ -0,0 +1,45 @@
+-- name: test_mv_rewrite_case_when_sum_widening_type
+-- Regression test for sync-MV rewrite of `sum(case when ... then col else 0 end)`
+-- when the MV stores `sum(col)` and the aggregator widens the column's type.
+-- Before the fix the rewritten plan kept the inner CASE WHEN / IF declared
+-- as the original (narrower) column type while the THEN branch was already
+-- the widened MV column, so any group whose sum exceeded the original type's
+-- range would be silently truncated at the outer SUM.
+create database db_${uuid0};
+use db_${uuid0};
+
+CREATE TABLE t1 (
+    k1 DATE NULL,
+    k2 INT  NULL,
+    k3 SMALLINT NULL
+) DUPLICATE KEY(k1)
+DISTRIBUTED BY HASH(k1) BUCKETS 1
+PROPERTIES("replication_num" = "1");
+
+CREATE MATERIALIZED VIEW test_mv1 AS
+  SELECT k1, k2, sum(k3) AS sum1 FROM t1 GROUP BY k1, k2;
+function: wait_materialized_view_finish()
+
+-- Per-(k1, k2) sum(k3) deliberately overflows SMALLINT (max 32767):
+--   for ('2024-01-01', k2=0) the sum is 30000+30000+30000+10000 = 100000.
+INSERT INTO t1 VALUES
+    ('2024-01-01', 0, 30000),
+    ('2024-01-01', 0, 30000),
+    ('2024-01-01', 0, 30000),
+    ('2024-01-01', 0, 10000),
+    ('2024-01-01', 1, 5);
+
+-- The query rewrites `case when k2=0 then k3 else 0` against test_mv1's
+-- mv_sum_k3 column.  After the fix, the rewritten IF/CASE WHEN result type
+-- is BIGINT (matching mv_sum_k3) so the outer sum is not truncated.
+SELECT k1,
+       sum(k3) AS sum1,
+       sum(case when k2=0 then k3 else 0 end) AS sum2
+FROM t1 GROUP BY k1;
+
+-- Same shape, expressed with IF instead of CASE WHEN.
+SELECT k1,
+       sum(if(k2=0, k3, 0)) AS sum_if
+FROM t1 GROUP BY k1;
+
+DROP DATABASE db_${uuid0};