code: func IsEQCondFromIn(expr Expression) bool {
  	sf, ok := expr.(*ScalarFunction)
  	if !ok || sf.FuncName.L != ast.EQ {
  		return false
  	}
  	cols := make([]*Column, 0, 1)
  	cols = ExtractColumnsFromExpressions(cols, sf.GetArgs(), isColumnInOperand)
  	return len(cols) > 0
  }
docs: // IsEQCondFromIn checks if an expression is equal condition converted from `[not] in (subq)`.