Implemented age_tail function (#1283)

age_tail() function returns a list containing all the elements,
excluding the first one, from a list.

age--1.4.0.sql

@@ -3590,6 +3590,14 @@ RETURNS NULL ON NULL INPUT
 PARALLEL SAFE
 AS 'MODULE_PATHNAME';
 
+CREATE FUNCTION ag_catalog.age_tail(variadic "any")
+RETURNS agtype
+LANGUAGE c
+IMMUTABLE
+RETURNS NULL ON NULL INPUT
+PARALLEL SAFE
+AS 'MODULE_PATHNAME';
+
 CREATE FUNCTION ag_catalog.age_properties(agtype)
 RETURNS agtype
 LANGUAGE c

regress/expected/expr.out

@@ -6928,6 +6928,45 @@ SELECT * from cypher('list', $$RETURN range(0, null, -3)$$) as (range agtype);
 ERROR:  range(): neither start or end can be NULL
 SELECT * from cypher('list', $$RETURN range(0, -10.0, -3.0)$$) as (range agtype);
 ERROR:  range() unsupported argument type
+-- tail()
+-- should return the last elements of the list
+SELECT * FROM cypher('list', $$ RETURN tail([1,2,3,4,5]) $$) AS (tail agtype);
+     tail     
+--------------
+ [2, 3, 4, 5]
+(1 row)
+
+SELECT * FROM cypher('list', $$ RETURN tail(["a","b","c","d","e"]) $$) AS (tail agtype);
+         tail         
+----------------------
+ ["b", "c", "d", "e"]
+(1 row)
+
+-- should return null
+SELECT * FROM cypher('list', $$ RETURN tail([1]) $$) AS (tail agtype);
+ tail 
+------
+
+(1 row)
+
+SELECT * FROM cypher('list', $$ RETURN tail([]) $$) AS (tail agtype);
+ tail 
+------
+
+(1 row)
+
+-- should throw errors
+SELECT * FROM cypher('list', $$ RETURN tail(123) $$) AS (tail agtype);
+ERROR:  tail() argument must resolve to a list or null
+SELECT * FROM cypher('list', $$ RETURN tail(abc) $$) AS (tail agtype);
+ERROR:  could not find rte for abc
+LINE 1: SELECT * FROM cypher('list', $$ RETURN tail(abc) $$) AS (tai...
+                                                    ^
+SELECT * FROM cypher('list', $$ RETURN tail() $$) AS (tail agtype);
+ERROR:  function ag_catalog.age_tail() does not exist
+LINE 1: SELECT * FROM cypher('list', $$ RETURN tail() $$) AS (tail a...
+                                               ^
+HINT:  No function matches the given name and argument types. You might need to add explicit type casts.
 -- labels()
 SELECT * from cypher('list', $$CREATE (u:People {name: "John"}) RETURN u$$) as (Vertices agtype);
                                       vertices                                       

regress/sql/expr.sql

@@ -2830,6 +2830,17 @@ SELECT * from cypher('list', $$RETURN range(-10, 10, -1)$$) as (range agtype);
 SELECT * from cypher('list', $$RETURN range(null, -10, -3)$$) as (range agtype);
 SELECT * from cypher('list', $$RETURN range(0, null, -3)$$) as (range agtype);
 SELECT * from cypher('list', $$RETURN range(0, -10.0, -3.0)$$) as (range agtype);
+-- tail()
+-- should return the last elements of the list
+SELECT * FROM cypher('list', $$ RETURN tail([1,2,3,4,5]) $$) AS (tail agtype);
+SELECT * FROM cypher('list', $$ RETURN tail(["a","b","c","d","e"]) $$) AS (tail agtype);
+-- should return null
+SELECT * FROM cypher('list', $$ RETURN tail([1]) $$) AS (tail agtype);
+SELECT * FROM cypher('list', $$ RETURN tail([]) $$) AS (tail agtype);
+-- should throw errors
+SELECT * FROM cypher('list', $$ RETURN tail(123) $$) AS (tail agtype);
+SELECT * FROM cypher('list', $$ RETURN tail(abc) $$) AS (tail agtype);
+SELECT * FROM cypher('list', $$ RETURN tail() $$) AS (tail agtype);
 -- labels()
 SELECT * from cypher('list', $$CREATE (u:People {name: "John"}) RETURN u$$) as (Vertices agtype);
 SELECT * from cypher('list', $$CREATE (u:People {name: "Larry"}) RETURN u$$) as (Vertices agtype);

src/backend/utils/adt/agtype.c

@@ -5126,6 +5126,83 @@ Datum age_last(PG_FUNCTION_ARGS)
     PG_RETURN_POINTER(agtype_value_to_agtype(agtv_result));
 }
 
+
+PG_FUNCTION_INFO_V1(age_tail);
+/*
+ * Returns a list  containing all the elements, excluding the first one, from a list.
+ */
+Datum age_tail(PG_FUNCTION_ARGS)
+{
+    Oid arg_type;
+    agtype *agt_arg = NULL;
+    agtype *agt_result = NULL;
+    agtype_in_state agis_result;
+    int count;
+    int i;
+
+    /* check number of arguments */
+    if (PG_NARGS() < 1 || PG_NARGS() > 1)
+    {
+        ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+                        errmsg("age_tail() requires only one argument")));
+    }
+
+    /* get the data type */
+    arg_type = get_fn_expr_argtype(fcinfo->flinfo, 0);
+
+    /* check the data type */
+    if (arg_type != AGTYPEOID)
+    {
+        ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+                        errmsg("age_tail() argument must be of type agtype")));
+    }
+
+    /* check for null */
+    if (PG_ARGISNULL(0))
+    {
+        PG_RETURN_NULL();
+    }
+
+    agt_arg = AG_GET_ARG_AGTYPE_P(0);
+    /* check for an array */
+    if (!AGT_ROOT_IS_ARRAY(agt_arg) || AGT_ROOT_IS_SCALAR(agt_arg))
+    {
+        ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+                        errmsg("tail() argument must resolve to a list or null")));
+    }
+
+    count = AGT_ROOT_COUNT(agt_arg);
+
+    /* if we have an empty list or only one element in the list, return null */
+    if (count <= 1)
+    {
+        PG_RETURN_NULL();
+    }
+
+    /* clear the result structure */
+    MemSet(&agis_result, 0, sizeof(agtype_in_state));
+
+    /* push the beginning of the array */
+    agis_result.res = push_agtype_value(&agis_result.parse_state,
+                                        WAGT_BEGIN_ARRAY, NULL);
+
+    /* iterate through the list beginning with the second item */
+    for (i = 1; i < count; i++)
+    {
+        agis_result.res = push_agtype_value(&agis_result.parse_state, WAGT_ELEM,
+                                            get_ith_agtype_value_from_container(&agt_arg->root, i));
+    }
+
+    /* push the end of the array */
+    agis_result.res = push_agtype_value(&agis_result.parse_state,
+                                        WAGT_END_ARRAY, NULL);
+
+    agt_result = agtype_value_to_agtype(agis_result.res);
+    pfree_agtype_value(agis_result.res);
+
+    PG_RETURN_POINTER(agt_result);
+}
+
 PG_FUNCTION_INFO_V1(age_properties);
 
 Datum age_properties(PG_FUNCTION_ARGS)