fix: support repeated named parameters

This fixes `got %v argument values, but found %v parameters in the sql string`
error when using repeated named arguments.

The "workaround" is to specify as many parameters
as observed. The last one will win due to
`prepareSpannerStmt` using map keyed by name.

Due to this change the `Bad` examples will
start to return an error.

Example:

```golang
// Bad: @name will be "value2"
s.db.QueryRow(
  "SELECT * FROM users WHERE (first_name=@name OR last_name=@name)",
  sql.Named("name", "value"),
  sql.Named("name", "value2"),
)

// Bad: @name will be "value2"
s.db.QueryRow(
  "SELECT * FROM users WHERE (first_name=@name OR last_name=@name)",
  "value",
  "value2",
)

// Good: works, ideal usage
s.db.QueryRow(
  "SELECT * FROM users WHERE (first_name=@name OR last_name=@name)",
  sql.Named("name", "value"),
)

// Good: not ideal, inferred positional arguments
s.db.QueryRow(
  "SELECT * FROM users WHERE (first_name=@name OR last_name=@name)",
  "value",
)
```

Signed-off-by: Kamil Trzciński <[email protected]>

statement_parser.go

@@ -46,6 +46,16 @@ func union(m1 map[string]bool, m2 map[string]bool) map[string]bool {
 	return res
 }
 
+// Use slices with Go 1.21
+func appendOnce(slice []string, item string) []string {
+	for _, s := range slice {
+			if s == item {
+				return slice
+			}
+	}
+	return append(slice, item)
+}
+
 // parseParameters returns the parameters in the given sql string, if the input
 // sql contains positional parameters it returns the converted sql string with
 // all positional parameters replaced with named parameters.
@@ -249,13 +259,13 @@ func findParams(positionalParamChar rune, sql string) (string, []string, error)
 				for index < len(runes) {
 					if !(unicode.IsLetter(runes[index]) || unicode.IsDigit(runes[index]) || runes[index] == '_') {
 						hasNamedParameter = true
-						namedParams = append(namedParams, string(runes[startIndex:index]))
+						namedParams = appendOnce(namedParams, string(runes[startIndex:index]))
 						parsedSQL.WriteRune(runes[index])
 						break
 					}
 					if index == len(runes)-1 {
 						hasNamedParameter = true
-						namedParams = append(namedParams, string(runes[startIndex:]))
+						namedParams = appendOnce(namedParams, string(runes[startIndex:]))
 						parsedSQL.WriteRune(runes[index])
 						break
 					}

statement_parser_test.go

@@ -516,6 +516,11 @@ func TestFindParams(t *testing.T) {
 			wantSQL: "SELECT * FROM PersonsTable @{FORCE_INDEX=my_index} WHERE id=@id AND name=@name",
 			want:    []string{"id", "name"},
 		},
+		{
+			input:   "SELECT * FROM PersonsTable@{FORCE_INDEX=`my_index`} WHERE id=@id AND (first_name=@name OR last_name=@name)",
+			wantSQL: "SELECT * FROM PersonsTable@{FORCE_INDEX=`my_index`} WHERE id=@id AND (first_name=@name OR last_name=@name)",
+			want:    []string{"id", "name"},
+		},
 		{
 			input:   `SELECT * FROM PersonsTable WHERE id=?`,
 			wantSQL: `SELECT * FROM PersonsTable WHERE id=@p1`,