How to get primary key of table?

Question

Is there a way to get the name of primary key field from mysql-database? For example:

I have a table like this:

id	name
1	Foo1
2	Foo2
3	Foo3

Where the field id is primary key (it has auto increment but I can't use that). How can I retrieve fields name "id" in php?

Answer 1

A better way is to use SHOW KEYS since you don't always have access to information_schema. The following works:

SHOW KEYS FROM table WHERE Key_name = 'PRIMARY'

Column_name will contain the name of the primary key.

Answer 2

Here is the Primary key Column Name

SELECT k.column_name
FROM information_schema.table_constraints t
JOIN information_schema.key_column_usage k
USING(constraint_name,table_schema,table_name)
WHERE t.constraint_type='PRIMARY KEY'
  AND t.table_schema='YourDatabase'
  AND t.table_name='YourTable';

Answer 3

SELECT kcu.column_name, kcu.ordinal_position
FROM   information_schema.table_constraints tc
INNER JOIN information_schema.key_column_usage kcu
ON     tc.CONSTRAINT_CATALOG = kcu.CONSTRAINT_CATALOG
AND    tc.CONSTRAINT_SCHEMA = kcu.CONSTRAINT_SCHEMA
AND    tc.CONSTRAINT_NAME = kcu.CONSTRAINT_NAME
WHERE  tc.table_schema = schema()             -- only look in the current schema
AND    tc.constraint_type = 'PRIMARY KEY'
AND    tc.table_name = '<your-table-name>'    -- specify your table.
ORDER BY kcu.ordinal_position

Answer 4

use:

show columns from tablename where `Key` = "PRI";

Answer 5

How about this:

SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'Your Database'
  AND TABLE_NAME = 'Your Table name'
  AND COLUMN_KEY = 'PRI';


SELECT COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_SCHEMA = 'Your Database'
  AND TABLE_NAME = 'Your Table name'
  AND COLUMN_KEY = 'UNI';

Answer 6

If you want to generate the list of primary keys dynamically via PHP in one go without having to run through each table you can use

SELECT TABLE_NAME, COLUMN_NAME
FROM INFORMATION_SCHEMA.key_column_usage 
WHERE table_schema = '$database_name' AND CONSTRAINT_NAME = 'PRIMARY' 

though you do need to have access to the information.schema to do this.

Answer 7

Shortest possible code seems to be something like

// $dblink contain database login details 
// $tblName the current table name 
$r = mysqli_fetch_assoc(mysqli_query($dblink, "SHOW KEYS FROM $tblName WHERE Key_name = 'PRIMARY'")); 
$iColName = $r['Column_name']; 

Answer 8

For a PHP approach, you can use mysql_field_flags

$q = mysql_query('select * from table limit 1');

for($i = 0; $i < mysql_num_fields(); $i++)
    if(strpos(mysql_field_tags($q, $i), 'primary_key') !== false)
        echo mysql_field_name($q, $i)." is a primary key\n";

Answer 9

I've got it, finally!

<?php

function mysql_get_prim_key($table){
    $sql = "SHOW INDEX FROM $table WHERE Key_name = 'PRIMARY'";
    $gp = mysql_query($sql);
    $cgp = mysql_num_rows($gp);

    if ($cgp > 0) {
        // Note I'm not using a while loop because I never use more than one prim key column
        $agp = mysql_fetch_array($gp);
        extract($agp);
        
        return($Column_name);
    } else {
        return(false);
    }
}

?>

Answer 10

I use SHOW INDEX FROM table ; it gives me alot of informations ; if the key is unique, its sequenece in the index, the collation, sub part, if null, its type and comment if exists, see screenshot here

Answer 11

MySQL has a SQL query "SHOW INDEX FROM" which returns the indexes from a table. For eg. - the following query will show all the indexes for the products table:-

SHOW INDEXES FROM products \G

It returns a table with type, column_name, Key_name, etc. and displays output with all indexes and primary keys as -

*************************** 1. row ***************************
        Table: products
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: product_id
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: 
   Index_type: BTREE
      Comment: 
Index_comment: 

To just display primary key from the table use :-

SHOW INDEXES FROM table_name WHERE Key_name = 'PRIMARY'

Answer 12

If you have spatial tables in your database, use:

SHOW KEYS FROM table WHERE Key_name = 'PRIMARY' OR Key_name = 'OGR_FID'

Answer 13

You should use PRIMARY from key_column_usage.constraint_name = "PRIMARY"

sample query,

SELECT k.column_name as PK, concat(tbl.TABLE_SCHEMA, '.`', tbl.TABLE_NAME, '`') as TABLE_NAME
FROM information_schema.TABLES tbl
JOIN information_schema.key_column_usage k on k.table_name = tbl.table_name
WHERE k.constraint_name='PRIMARY'
  AND tbl.table_schema='MYDB'
  AND tbl.table_type="BASE TABLE";

Answer 14

SELECT k.column_name
FROM information_schema.key_column_usage k   
WHERE k.table_name = 'YOUR TABLE NAME' AND k.constraint_name LIKE 'pk%'

I would recommend you to watch all the fields