从MYSQL获取数据时如何从逗号分隔的数组中获取单个值

Question

I am entering data in data base like this:

ID | Name | Email   | Place
1  | Khan | abc@... | Page1, Page2, Page10

Now I am fetching data like this :

$conn = mysqli_connect($servername, $username, $password, $dbname);
$sql = "SELECT * FROM story Where Place='Page2' Limit 1";
$result = mysqli_query($conn, $sql);
$row = mysqli_fetch_assoc($result);

But unfortunately it show me nothing :(

I am uploading this Place row in comma separated form, now I want it show me the data where I select place.

Answer 1

Please consider normalizing your data. Is storing a delimited list in a database column really that bad? The design you have here will make you crazy if your application actually grows.

In the meantime, you want to use column LIKE '%value%' in place of column = 'value' . Beware: the performance of this kind of query is very bad and can't be improved.

EDIT Queries using column = 'value' or even column LIKE 'value%' can exploit indexes in the database management system. It's possible to look up values in an index in O(log(n)) time. That permits even a vast table, with billions of rows, to be accessed efficiently. However, a query containing column LIKE '%value%' has to scan through all the data, row by row, exhaustively looking for matches, in O(n) time. If you have a few hundred rows you won't notice this poor performance. But if your table grows you will definitely be sorry.

Try this query.

     SELECT * 
       FROM table
      WHERE column LIKE CONCAT('%' , 'Page2', '%')
      LIMIT 1

I suggested the use of CONCAT() so the query can easily be modified to use bind parameters. For example, CONCAT('%' ,? , '%')

Another edit. If you have Page1, Page100, Page101 you'll get a lot of false positive matches on Page1 . In MySQL FIND_IN_SET() can do a search of a comma-separated string.

     SELECT * 
       FROM table
      WHERE FIND_IN_SET('Page2', column) <> 0
      LIMIT 1

This will not work if you have spaces after your commas. Page1,Page2,Page3 is fine, but Page1, Page2, Page3 is no good. We can patch that problem like so.

     SELECT * 
       FROM table
      WHERE FIND_IN_SET('Page2', REPLACE(column, ', ', ',')) <> 0
      LIMIT 1

But now things are getting out of hand. What if you have two spaces after a comma someplace? Or three?

This too is an unoptimizable search.

Answer 2

A move toward data normalization.

A proposed junction table (eradicates the Place CSV column):

create table story_place_jnc
(   -- one row per story/place combo
    id int auto_increment primary key,
    storyId int not null,
    place varchar(20) not null  -- you size this thing

    -- perhaps 2 FK's go here (1 to story, 1 to place):

    -- Unique composite key on (storyId,place):
);

As Patsy said in Monty Python's Holy Grail, "It's only a model."

Who knows if you even have a place table :>