code: func (c *index) Delete(sc *stmtctx.StatementContext, m kv.Mutator, indexedValues []types.Datum, h int64, ss kv.Transaction) error {
  	key, _, err := c.GenIndexKey(sc, indexedValues, h, nil)
  	if err != nil {
  		return err
  	}
  	err = m.Delete(key)
  	if ss != nil {
  		switch c.idxInfo.State {
  		case model.StatePublic:
  			// If the index is in public state, delete this index means it must exists.
  			ss.SetAssertion(key, kv.Exist)
  		default:
  			ss.SetAssertion(key, kv.None)
  		}
  	}
  	return err
  }
docs: // Delete removes the entry for handle h and indexdValues from KV index.