How much do you know about the function of PHP braces?

/**
 *php braces example solution
 *site http://bbs.it-home.org
*/
$arr=array(0=>123, 'name'=>'Little Pig');
foreach($array as $k =>$v){
 echo "select * from blog_blogs where blog_tags like '%{$arr[$k]}%' order by blog_id"; //Adding a curly bracket just serves as the variable identifier
}
 echo '';
foreach($ array as $k=>$v){
 echo "select * from blog_blogs where blog_tags like '%{{$arr[$k]}}%' order by blog_id"; //Add two curly brackets, outer layer will be treated as ordinary characters
}
//Use curly brackets to distinguish variables
//echo "$arr['name']";//Using this sentence will report a syntax error
echo "{$arr['name'] }";//This sentence is normal. The characters in the curly brackets will be treated as variables
//$str{4} is followed by {} after the variable of the string. Curly brackets and square brackets are the same as a certain character. String variables are treated as arrays
$str = 'abcdefg';
echo $str{4};
?>