branch-4.0: [fix](substring) Fix substring_index #60346 (#60373)

Cherry-picked from #60346

Co-authored-by: Gabriel <liwenqiang@selectdb.com>

Author: github-actions[bot]

be/src/vec/functions/function_string.h

@@ -1897,7 +1897,7 @@ class FunctionSubstringIndex : public IFunction {
         }
 
         for (size_t i = 0; i < input_rows_count; ++i) {
-            auto str = str_col->get_data_at(i);
+            auto str = str_col->get_data_at(content_const ? 0 : i);
             auto delimiter = delimiter_col->get_data_at(delimiter_const ? 0 : i);
             int32_t delimiter_size = delimiter.size;
 

regression-test/data/function_p0/test_substring_index.out

@@ -46,3 +46,7 @@
 -- !sql --
 				test|test	test|test
 
+-- !sql --
+
+
+

regression-test/suites/function_p0/test_substring_index.groovy

@@ -134,4 +134,26 @@ suite("test_substring_index") {
     """
 
     sql "DROP TABLE IF EXISTS test_substring_index"
+
+    sql "DROP TABLE IF EXISTS test_substring_index2"
+    sql """
+    CREATE TABLE test_substring_index2 (
+        id INT,
+        str VARCHAR(100),
+        delimiter VARCHAR(10)
+    ) ENGINE=OLAP
+    DUPLICATE KEY(id)
+    DISTRIBUTED BY HASH(id) BUCKETS 1
+    PROPERTIES (
+        "replication_allocation" = "tag.location.default: 1"
+    )
+    """
+
+    sql """
+    INSERT INTO test_substring_index2 VALUES
+        (1, NULL, NULL),
+        (2, NULL, NULL)
+    """
+    qt_sql """ SELECT  SUBSTRING_INDEX(IFNULL(a.str, ''), ',', a.id) from test_substring_index2 a """
+    sql "DROP TABLE IF EXISTS test_substring_index2"
 }