如果DB表中存在数据，如何更新[重复]

Question

This question already has an answer here:

• SQL - IF EXISTS UPDATE ELSE INSERT INTO 1 answer

  if (isset($_POST["sendComments"]) ) {
    $whichProjectToSave= mysqli_real_escape_string($db5, $_POST['whichProjectToSave']);
    $commentsToPHP= mysqli_real_escape_string($db5, $_POST['commentsToPHP']);
    $objectName= mysqli_real_escape_string($db5, $_POST['objectName']);
    $sql="INSERT INTO   objectsCommentsTable (objectsCommentsText,projectName,objectName) VALUES('$commentsToPHP','$whichProjectToSave','$objectName')";
    // $sql="UPDATE objectsCommentsTable  SET objectsCommentsText ='$commentsToPHP'  WHERE projectName= '$whichProjectToSave' AND objectName = '$objectName' ";
   mysqli_query($db5,$sql);
                                  }

I have to update if data exists. But i know only how to use method above. Actually i can only insert data in table as first and then update it with changing of code. But i would like to use something like in code below. How can it be performed?

 IF EXISTS ( SELECT objectsCommentsText FROM objectsCommentsTable  WHERE objectName='$objectName' AND projectName = '$projectName')
    UPDATE objectsCommentsTable
    SET objectsCommentsText ='$commentsToPHP'
    WHERE projectName= '$whichProjectToSave' AND objectName = '$objectName' 
ELSE 
  INSERT INTO   objectsCommentsTable (objectsCommentsText,projectName,objectName) 
  VALUES('$commentsToPHP','$whichProjectToSave','$objectName')

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Answer 1

First, add unique index:

ALTER TABLE objectsCommentsTable ADD UNIQUE project_object_unique (projectName, objectName);

This will prevent adding rows with same projectName and objectName, and make ON DUPLICATE work.

Then, you can edit your query to use ON DUPLICATE

INSERT INTO objectsCommentsTable
(objectsCommentsText, projectName, objectName) VALUES ('$commentsToPHP','$whichProjectToSave', '$objectName')
ON DUPLICATE KEY
   UPDATE objectsCommentsText='$commentsToPHP'