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parser.go

@@ -2492,6 +2492,11 @@ func (p *Parser) parseCreateVectorIndex(pos token.Pos) *ast.CreateVectorIndex {
 	p.expect("(")
 	columnName := p.parseIdent()
 	p.expect(")")
+
+	// It only allows `WHERE column_name IS NOT NULL` for now, but we still relax the condition
+	// by reusing the `parseWhere` function for sake of it may be extended more conditions in the future.
+	//
+	// Reference: https://cloud.google.com/spanner/docs/reference/standard-sql/data-definition-language#vector_index_statements
 	where := p.tryParseWhere()
 	options := p.parseVectorIndexOptions()