(PHP 4 >= 4.3.0, PHP 5, PHP 7)
pg_meta_data — 获得表的元数据
$connection
, string $table_name
)pg_metadata() 以数组形式返回 table_name 表的定义。
此函数是实验性的。此函数的表象，包括名称及其相关文档都可能在未来的 PHP 发布版本中未通知就被修改。使用本函数风险自担 。
connectionPostgreSQL database connection resource.
table_nameThe name of the table.
以数组 array 形式返回表的定义，如果出错则返回 FALSE。
Example #1 取得表的元数据
<?php
$dbconn = pg_connect("dbname=publisher") or die("Could not connect");
$meta = pg_meta_data($dbconn, 'authors');
if (is_array($meta)) {
echo '<pre>';
var_dump($meta);
echo '</pre>';
}
?>
以上例程会输出：
array(3) {
["author"]=>
array(5) {
["num"]=>
int(1)
["type"]=>
string(7) "varchar"
["len"]=>
int(-1)
["not null"]=>
bool(false)
["has default"]=>
bool(false)
}
["year"]=>
array(5) {
["num"]=>
int(2)
["type"]=>
string(4) "int2"
["len"]=>
int(2)
["not null"]=>
bool(false)
["has default"]=>
bool(false)
}
["title"]=>
array(5) {
["num"]=>
int(3)
["type"]=>
string(7) "varchar"
["len"]=>
int(-1)
["not null"]=>
bool(false)
["has default"]=>
bool(false)
}
}
To specify a schema as well as a table name, use the "schemaname.tablename" form as usual for PostgreSQL and the other functions in this extension. Without the prefix, of course, the default schema search path is used.
<?php
$meta = pg_meta_data($dbconn, 'foo.bar'); // table "bar" in schema "foo"
if (is_array($meta)) {
var_dump($meta);
}
?>
The built in function does not provide any support for selecting a schema. If you need schema support and do not want to alter your SEARCH_PATH, the following function can provide it:
function meta_data($table, $schema = 'public')
{
$result = pg_query_params("SELECT a.attname, a.attnum, t.typname, a.attlen, a.attnotNULL, a.atthasdef, a.attndims
FROM pg_class as c, pg_attribute a, pg_type t, pg_namespace n
WHERE a.attnum > 0
AND a.attrelid = c.oid
AND c.relname = $1
AND a.atttypid = t.oid
AND n.oid = c.relnamespace
AND n.nspname = $2
ORDER BY a.attnum", array($table, $schema));
$fields = array();
while($row = pg_fetch_array()) {
$fields['attname'] = $row;
}
return $fields;
}
You can get some possibly more useful information with the query:
SELECT table_name, column_name, data_type, character_maximum_length FROM information_schema.columns WHERE table_name='tablename';
When querying on meta data from a temp table, the meta data seems to persist even if a fresh connection is established, where the temp table no longer exists.
For example, if you create a connection and a temp table like so:
$dbconn1 = pg_connect('blah blah', , PGSQL_CONNECT_FORCE_NEW);
pg_exec($dbconn1,'create temp table foo as select 'foo' as namecol, 'bar' as valcol');
Then create a new connection
$dbconn2 = pg_connect('blah blah', , PGSQL_CONNECT_FORCE_NEW);
And query the meta data for table 'foo' in this new connection, it will report the facts about this table:
pg_meta_data($dbconn2,'foo');
"'Array ( [foo] => Array ( [num] => 1 [type] => varchar... "
However, trying to remove this table:
pg_exec($dbconn,'drop table foo');
Throws an error:
pg_exec(): Query failed: ERROR: table "foo" does not exist in ...
This function seems to be case-sensitive on tablename (php-4.3.1)
The Array returned is of the following structure
['field name'] => Array
(
['num'] => Field number starting at 1
['type'] => data type, eg varchar, int4
['len'] => internal storage size of field. -1 for varying
['not null'] => boolean
['has default'] => boolean
)
......
for Varied size datatypes (varchar, text, etc)
you can get the max data length from the system table pg_attribute.atttypmod -4
eg.
select attnum, attname , atttypmod -4 as field_len
from pg_attribute, pg_class
where relname='$tablename'
and attrelid=relfilenode
and attnum>=1