sql/vecindex: make hnsw alias for cspann for index creation

This commit adds `hnsw` to the accepted list of index types when a
vector index is defined using the `USING` syntax. However, we will
silently provide a `cspann` index instead. This change is made in
anticipation of third-party tools that want to use `cspann`.

Fixes #143109

Release note (sql change): When creating a vector index via the `USING`
syntax, is is now possible to specify `hnsw` as the index type, although
a `cspann` vector index will still be provided. The goal of this change
is to increase compatibility with third-party tools.

Author: DrewKimball

pkg/sql/logictest/testdata/logic_test/vector_index

@@ -38,6 +38,10 @@ ALTER TABLE simple ALTER PRIMARY KEY USING COLUMNS (b)
 statement notice CREATE VECTOR INDEX will disable writes to the table while the index is being built
 CREATE INDEX ON simple USING cspann (vec1 ASC);
 
+# We allow hnsw as an alias for cspann.
+statement ok
+CREATE INDEX ON simple USING hnsw (vec1);
+
 query TT
 SHOW CREATE TABLE simple
 ----
@@ -50,6 +54,7 @@ simple  CREATE TABLE public.simple (
           VECTOR INDEX simple_vec1_idx1 (vec1 vector_l2_ops),
           UNIQUE INDEX simple_a_key (a ASC),
           VECTOR INDEX simple_vec1_idx2 (vec1 vector_l2_ops),
+          VECTOR INDEX simple_vec1_idx3 (vec1 vector_l2_ops),
           FAMILY fam_0_a_vec1_b (a, vec1, b)
         )
 
@@ -312,8 +317,8 @@ statement error vector indexes don.t support stored columns
 CREATE VECTOR INDEX on vec_errors (vec1) STORING (b);
 
 # Try to use unsupported vector index type.
-statement error at or near "hnsw": syntax error: unrecognized access method: hnsw
-CREATE INDEX ON vec_errors USING hnsw (vec1)
+statement error at or near "ivfflat": syntax error: unrecognized access method: ivfflat
+CREATE INDEX ON vec_errors USING ivfflat (vec1)
 
 # Operator classes other than vector_l2_ops are not (yet) supported.
 statement error pgcode 0A000 pq: unimplemented: operator class vector_l1_ops is not supported

pkg/sql/parser/sql.y

@@ -12394,7 +12394,7 @@ opt_index_access_method:
         val = idxtype.INVERTED
       case "btree":
         val = idxtype.FORWARD
-      case "cspann":
+      case "cspann", "hnsw":
         val = idxtype.VECTOR
       case "hash", "spgist", "brin":
         return unimplemented(sqllex, "index using " + $2)

pkg/sql/parser/testdata/create_index

@@ -532,3 +532,11 @@ CREATE VECTOR INDEX a ON b (c) WITH ('build_beam_size' = 16, 'min_partition_size
 CREATE VECTOR INDEX a ON b (c) WITH ('build_beam_size' = (16), 'min_partition_size' = (8), 'max_partition_size' = (32)) -- fully parenthesized
 CREATE VECTOR INDEX a ON b (c) WITH ('build_beam_size' = _, 'min_partition_size' = _, 'max_partition_size' = _) -- literals removed
 CREATE VECTOR INDEX _ ON _ (_) WITH ('build_beam_size' = 16, 'min_partition_size' = 8, 'max_partition_size' = 32) -- identifiers removed
+
+parse
+CREATE INDEX a ON b USING HNSW (c)
+----
+CREATE VECTOR INDEX a ON b (c) -- normalized!
+CREATE VECTOR INDEX a ON b (c) -- fully parenthesized
+CREATE VECTOR INDEX a ON b (c) -- literals removed
+CREATE VECTOR INDEX _ ON _ (_) -- identifiers removed