code: func (t *Table) ColumnEqualRowCount(sc *stmtctx.StatementContext, value types.Datum, colID int64) (float64, error) {
  	c, ok := t.Columns[colID]
  	if !ok || c.IsInvalid(sc, t.Pseudo) {
  		return float64(t.Count) / pseudoEqualRate, nil
  	}
  	result, err := c.equalRowCount(sc, value, t.ModifyCount)
  	result *= c.GetIncreaseFactor(t.Count)
  	return result, errors.Trace(err)
  }
docs: // ColumnEqualRowCount estimates the row count where the column equals to value.