code: func (c *compareFunctionClass) getFunction(ctx sessionctx.Context, rawArgs []Expression) (sig builtinFunc, err error) {
  	if err = c.verifyArgs(rawArgs); err != nil {
  		return nil, err
  	}
  	args := c.refineArgs(ctx, rawArgs)
  	cmpType := GetAccurateCmpType(args[0], args[1])
  	sig, err = c.generateCmpSigs(ctx, args, cmpType)
  	return sig, err
  }
docs: // getFunction sets compare built-in function signatures for various types.